Abstract: Canon EOS FAQ v2.4

Bob Atkins Photography
EOS FAQ v2.4


CANON EOS FAQ Version 2.4
Date: November 1993

All original material is Copyright © 1992, 1993, 1994, 1995 Alvin Chia-Hua Shih and Robert M. Atkins.

4. Lenses:

  1. Lens Specifications?
  2. For a comprehensive chart of Canon lens offerings, please consult an EF lens guide, such as the one found in the "EF Lenses" brochure. Per Danielsson has posted data on many EF lenses and his table is given in Appendix B at the end of this FAQ.

    Alvin Shih has also abstracted information on EF lenses and his table is given in Appendix C at the end of this FAQ.

    The following lenses were announced in the USA on Feb 17th 1993. The information below was supplied by Chuck Westfall of Canon:

    Canon U.S.A., Inc. announced 3 new EF lenses at the 1993 PMA (Photo Marketing Assn.) dealer trade show in Atlanta. The new lenses are: EF 20-35mm f/3.5-4.5 USM, EF 50mm f/1.4 USM, & EF 400mm f/5.6L USM. Here are the basic specifications:

    Specification       20-35/3.5-4.   50/1.4         400/5.6L
    AF Drive            Ring USM       Micro USM      Ring USM
    (Groups/Elements)   11/12          6/7            6/7
    Min Focus Distance  1.1 ft/0.34m   1.5 ft/0.45m   11.5 ft/3.5m
    Length              2.7 in/69mm    2.0 in/50.5mm  10.1 in/257mm
    Weight              12 oz/340gr    10.2 oz/290gr  43.8oz/1.25kg
    Filter Size         77mm           58mm           77mm
    List Price          $725           TBD            TBD

    The EF 20-35mm f/3.5-4.5 USM was designed as an easy-to-use wide-angle zoom lens at a more affordable price. The new lens features internal zooming and focusing to help maintain its compact size and light weight, while providing a non-rotating filter thread for use with a circular polarizer or other special effects filter. The USM provides quick, silent AF with a full-time manual focus override.

    The EF 50mm f/1.4 USM meets the needs of a wide range of advanced amateur and professional photographers, due to its large aperture, light weight and compact design. The optical quality of the new lens exceeds that of the FD 50mm f/1.4, with even greater contrast and resolution. The new lens is equipped with Canon's latest Micro USM focus drive for high-speed, silent AF, with a full-time mechanical manual focus override for added creative control. Other features include a metal mount, distance and depth of field scales and an IR index.

    The EF 400mm f/5.6L USM is targeted to professional and advanced amateur photographers who require a compact, lightweight and easy-to-handle long telephoto lens for a variety of outdoor applications. The lens uses a rear-focusing optical system and Canon USM (Ultrasonic Motor) technology for silent, high-speed autofocusing. The EF 400mm f/5.6L USM has 7 elements in 6 groups, including two elements of Canon's Ultra-Low Dispersion (UD) glass. This is the first EF telephoto to use Canon's newly-developed "Super UD" glass. The new glass features dispersion characteristics similar to fluorite, producing outstanding resolution, contrast and color fidelity.

    A full-time mechanical manual focusing mechanism makes it possible to switch to manual focusing at any time without switching out of AF mode. Dual rubber manual focusing rings are positioned on both the large and small sections of the lens barrel to provide improved operability. A sliding lens hood is built-in and the new lens is equipped with a focusing range selector switch and a detachable tripod collar. The EF 400mm f/5.6L USM is compatible with both EF Extenders for autoexposure and manual focus.

    The EF 20-35mm f/3.5-4.5 USM will be available through authorized Canon USA dealers by the end of March. The EF 50mm f/1.4 USM & EF 400mm f/5.6L USM will be available by the end of June, with pricing determined at that time.


  3. Why does Canon offer so many different lenses, some of which seem quite similar?
  4. Though Canon offers lenses of similar focal lengths, they are targeted at different audiences. Canon has 3 broad categories of lenses: A, B,and L.

    The "A-series" consists of low-cost lenses for the "snapshooter" market.The original A-series consisted of lenses which were AF-only for use on the 700 and 800 series. They had no manual focus capability of any sort, and also lacked focusing scales. These lenses marked with an "A" after the focal length and aperture designations. For example, "100-200/4.5A".

    The new "A-series" does allow for manual focus, and may even sport USM, but still lack focusing scales, and are not designed to be as durable as other EF lenses. They no longer have an "A" in their lens designation. Indeed, the lens mounts of all but the longer lenses are polycarbonate instead of metal. The optical performance is reasonable for the money.

    At the other end, there is the "L" series. The "L" designates "Luxury" (or as Mike Coren would say, "Life's savings" :-). These lenses are targeted towards professionals or advanced amateurs. L-series lenses typically include special elements of UD or Fluorite glass for outstanding optical performance. Some lenses of this series are also designed to withstand the abuse which comes with professional photography (photojournalism in particular). They are generally sold complete with case and lens hood.

    Any lenses which fall in between are simply in the "B-series". These lenses are generally reasonable value for the money and should serve the typical "enthusiast" quite well. They all include manual focus capability, and distance scales as well.

    Outside of the three major categories, there is the class of "special-purpose" lenses. These include the TS-E lenses (the 24mm is an "L", but the 45mm and 90mm are not), as well as the macro lenses.

    ACS (RMA)

  5. Can I use my FD-mount lenses on EOS bodies?
  6. There is a mount converter from EOS to FD, but it is a MACRO converter only! That is to say, it does not allow the fitted FD-mount lens to focus to infinity. In addition, it does not work with cameras that do not have interchangeable focusing screens, and certain FD lenses might not fit! Ask Canon for the list of incompatible lenses before investing in an FD-macro setup.

    Available from Canon Professional Services ONLY, there is a 1.26x teleconverter for certain 200mm+ lenses (and the FD50-300/4.5L, the FD85-300/4.5 and FD150-600/5.6L) which also functions as a mount adaptor. Part number (item code)is C54-2131, and the cost is $240. However, this costs 2/3 stop, and only stopped-down, metering is available. (No autofocus, of course.). There are also metering restrictions on many cameras. The EOS 1 works best, but the 620,630,650/RT series also work well with the Focusing Screens E-D and E-H and will work with E-I. Screens E-A, E-B, E-C(standard) and E-L are not recommended. The EOS 1 can be used in Tv, Av, Manual, Depth and Program exposure modes, but other EOS cameras require the use of the Av mode if TTL meteing is to be used. Manual metering is not recommended exept for the EOS-1, and even on the EOS-1 spot metering cannot be used. The 10s also requires exposure compensation to correct for metering errors when used with the FD->EOS converter. The compensation depends on the lens aperture and the metering mode, varying from -0.3 stops with an f/1.8 lens setting and partial metering to +0.9 stops with an f/16 lens setting and partial meteing, and from 0 stops with an f/1.8 lens setting and evaluative metering to +0.8 stops with an f/16 lens setting and evaluative metering. The 620 and 650 require +0.5 stops of exposure compensation. The 630 and RT (with the correct screens) require no exposure compensation.

    I do not currently have data on the Elan or A2/A2E/5 operation with the FD->EOS converter. If you need more information and/or current price and availablity you will need to contact Canon Professional Services at (516) 488 1400 (x3354) or (516) 328 4831.

    Also see section 9.18


  7. Can I use EF-mount lenses on FD-mount bodies?
  8. No. First, the EF mount is bigger than the FD mount. Second, the adaptor would have to convert the mechanical aperture setting action for the old FD lenses into electrical information for the EF lenses. Since you can't stop down an EF lens mechanically, even if you had stopped-down metering, you'd still be stuck. It would require quite the contraption to make EF lenses work, and is probably not worth anyone's effort to research and develop.


  9. Why have the focusing motor in the lens?
  10. Having the focusing motor in the lens allows the lens to have a motor that is "matched" to its focusing characteristics. Heavier glass can be supplied with more powerful motors. It should also simplify lens design since there is no need to design a transmission that takes mechanical energy from a fixed point in the lens mount to some other point in the lens. With the motor in the lens, the motor can be placed where ever it will be most effective.


  11. Doesn't the motor in the lens make the lenses more expensive?
  12. In some cases, it probably does. If the retail prices of third-party lenses is any indication, the motor does cost something (comparing a 3rd-party Nikon AF mount lens to its Canon EF mount equivalent). However, the lenses from Canon are generally regarded as faster focusing, so it may be worth the extra money.


    Note that some recent lenses (e.g. Sigma 70-210/2.8 APO) are priced exactly the same in manual and all AF (Nikon, Minolta, Canon) mounts, so maybe the 3rd party manufacturers have refined their design and manufacturing costs to the point where the cost of the internal lens motor is not significant.


  13. Manual focusing with USM lenses?
  14. There are two varieties of USM lenses. One variety, commonly found on some of the "L" series lenses, converts rotation of the manual focusing ring into electrical pulses, which in turn are converted into motor movement. On such lenses, the ring is referred to as an "electronic focusing ring". The benefit of this system is that some of the "L" lenses can be set to different focusing ring sensitivities to allow for speed or precision as the user requires.

    By default, the electronic focusing ring is disabled after AF since leaving it enabled draws significant amounts of power from the battery. However, on some bodies, the electronic focusing ring can be left enabled via CF after AF for "fine tuning" of focus by the user.

    Most other USM lenses have a mechanical coupling that works after AF regardless of the custom function setting. Though this draws no battery power, the angle of rotation from close-focus to infinity is usually regarded as too short.


  15. Can small animals hear USM lenses?
  16. In a survey taken by Mike Coren, it would appear that some animals can detect USM noise at close range, but are not annoyed by it. Indeed, some animals may be even curious. However, there was one report of a cat who is particularly annoyed by the 28-80/2.8-4L. This may be an exception.

    The lenses in the sample population were:

    85mm f/1.2 L - 1
    300mm f/4.0 L - 1
    28-80mm f/3.5-5.6 - 2
    28-80mm f/2.8-4.0 L - 1
    28-105mm f/3.5-4.5 - 1
    35-105mm f/4-5.6 - 2
    70-210mm f/3.5-4.5 - 2
    75-300mm f/4.0-5.6 - 1
    100-300mm f/4.5-5.6 - 1

  17. Is there any way to focus a USM lens without making any ultrasonic noise?
  18. On USM lenses with electronic focusing rings, it appears not. On USM lenses with mechanical couplings, use manual focus.


  19. Canon lenses look too expen$ive. What about third-party?
  20. Because of the built-in motor, 3rd party lenses for EOS are generally more expensive than their non-EOS counterparts.

    Canon has been pretty secretive about their lens interface. There have been a few postings to the net implying that Sigma lenses don't AF very well on Canon EOS cameras, or if they do, they only do so for a limited time before failing. On the other hand many users are very happy with Sigma lenses and report no problems at all. Failures may just be isolated cases.

    Generally, Canon lenses are of similar or better quality in comparison to similarly priced competitors. It is probably better to stick with Canon lenses unless (a) Canon don't make the lens you want, or (b) You just can't afford the Canon lens. There is no 3rd party lens which uses the USM technology - a big reason to go with Canon.

    There are rumours that the Tamron 28-200/3.8-5.6 uses licensed technology to ensure correct operation on EOS bodies. These rumours are unconfirmed.


  21. Why didn't Canon think of using distance information (like some other nameless company :-)?
  22. Well, many lenses do return distance information, though it is not currently used for much. Who knows what it might be used for in future EOS cameras?

    Here's a current list of EF lenses with absolute distance data. The one thing most of these lenses have in common is ring USM with full-time mechanical manual focus:

    EF 14mm f/2.8L (USM)
    EF 20mm f/2.8 (USM)
    EF 85mm f/1.8 (USM)
    EF 100mm f/2 (USM)
    EF 100mm f/2.8 Macro
    EF 200mm f/2.8L (USM)
    EF 300mm f/4L (USM)
    EF 400mm f/5.6L (USM)
    EF 20-35mm f/3.5-4.5 (USM)
    EF 28-70mm f/2.8L (USM)
    EF 28-80mm f/3.5-5.6 (USM)
    EF 28-105mm f/3.5-4.5 (USM)
    EF 35-135mm f/4-5.6 (USM)
    EF 35-350mm f/3.5-5.6L (USM)
    EF 70-210mm f/3.5-4.5 (USM)
    EF 100-300mm f/4.5-5.6 (USM)

    The distance info is not currently used anywhere except the close-up and portrait PIC modes, and then only with the Elan and the 10s (not the Rebel series or the A2/A2E.). Whether some future EOS body will use this information is a matter for speculation.


  23. So which lenses are worth getting?
  24. A list of lens ratings given by the French photo magazine "Chasser d'Images" and was submitted to the FAQ by Christian Decurnex. It can be found at the end of this FAQ in Appendix F. This is probably the most complete survey of Canon EF series lenses. Many thanks to Christian for sending it in to the FAQ.

    Christian has also abstracted the Chasseur d'Images tests of all the Canon EF lenses, and his posting can be found in Appendix H at the end of this FAQ ###

    George Lepp in his "Natural Image" newsletter tests lenses from time to time. Most of the tests are on Canon and Nikon lenses, but he also tests 3rd party lenses as well as a few from Minolta, Pentax etc. He also tests cameras and film and the "Natural Image" carries articles on all aspects of nature and wildlife photography. For subscriptions and back issue information contact Lepp and Associates, P.O. Box 6240, Los Osos, CA 93412 or call (805) 528-7385. His lens rating scheme is from 0 to 10, with 6.0 representing the bottom end of his "professional quality" range. 6.0 corresponds to somewhere around 60 lp/mm. A rating of 10 would usually be for the best macro lenses, sharp from edge to edge and resolving 130 lp/mm+. None of his tests on any of the Canon lenses have given numbers less than 6.0. The "regular" lenses usually are in the 7-7.5 range, while the good "L" series lenses rate in the 8-9 range.

    The following numbers are MY attempt at averaging his test numbers. He usually tests at several focal lengths (for zooms) and several apertures. The numbers given here are my averages of his numbers over various focal lengths (for zooms) and over several tests (for those lenses tested more than once). Numbers are given for wide-open (W-O) and at f/5.6. Mistakes are mine, not George Lepp's. For more information see the address and phone numbers above. Note that you cannot sum up the qualities of a lens in a single number, so take these numbers as a very general guideline only. Get the original tests for more information.

    Lens                          W-O                 f/5.6

    EF300/2.8L* 8.0 9.0 EF300/4L* 8.0 8.5 EF200/2.8L* 7.5 9.0 EF500/4.5L 7.0 7.5 (est) EF100-300/5.6L* 8.5/8.0 8.5/8.0 EF100-300/4.5-5.6USM* 7.0/7.0 8.0/7.0 EF70-210/3.5-4.5* 7.0/7.0 8.5/7.5 EF35-350/3.5-5.6L 7.0 7.5 EF80-200/2.8L* 7.5/7.5 9.0/9.0 EF28-70/3.5-4.5II average "overall" rating 8.25 - Tamron SP 300/2.8 EDIF 7.0 8.0 Tamron SP 70-210/2.8 LD 6.5/6.5 7.5/7.0 Sigma 400/5.6 APO 6.5 6.5 Sigma 500/7.2 APO 5.5 -

    A/B refers to ratings at the short (A) and long (B) ends of the zoom range.

    Many of these lenses (marked "*"), along with Canon, Tamron and Vivitar teleconverters (see section 4.16) were tested in issue 28 of "The Natural Image" (Winter 1991). Also in the same issue are tests on similar Nikon lenses, so you can get ammunition for the Canon vs. Nikon wars! For directly comparable lenses, the Canons seemed to have a slight edge in sharpness. On repeat tests some sight variations have appeared. For example in earlier tests, at 300mm and at f/5.6, the 100-300L has tested as high as 8.5, while the 100-300USM has tested as low as 6.5. At the level at which ordinary mortals (without access to a full optics testing lab) can test lenses, such small differences are to be expected from test to test. George has commented though, that in general, the test results are quite repeatable.

    From his test results George has stated that the Canon 300/2.8L and the Canon 100-300L are the sharpest lenses in their category from any manufacturer.

    Of notable non-Canon lenses, the Sigma 400/5.6 APO rates a 6.5 wide open (f/5.6), and the Sigma 500/7.2 APO rates a 5.5 wide open (f/7.2), and a 6.0 at f/8 (1/3 stop down). The 400/5.6 APO represents good value for money and can yield quite acceptable images. The Canon 400/5.6L has been released but there are no tests to date (11/93). I would expect it to significantly outperform the Sigma lens, but at maybe 3 times the cost (ca. $1400).

    Again, use these numbers with some thought. They are general guidelines only and should not be taken as the definitive word on the quality of these lenses. Sharpness is not the only factor in choosing a lens (though for me it is of major importance). George Lepp's rating are weighted strongly by central image resolution and contrast.



    Popular Photography has also tested quite a large number of Canon EF series lenses (and other 3rd party EOS compatible lenses). The tests are too detailed to summarize here. Check out back issues (some libraries may have them). A brief (entirely insufficient) one-letter summary of their full page tests follows. A = Well above average, B = Above average, C = Slightly above average, D = Average. Note that "Average" doesn't really mean average in Popular Photography, since almost no lenses are below "average". It probably means "acceptable" in some general sense! Note that there are many inconsistencies in the Pop Photog tests. The numerical data does not always agree with the written comments. Look at the tests in detail (especially the hard data) rather than relying on their (or my) comments.

    EF85/1.8 USM        April 1993     A
    EF14/2.8L USM       January 1993   D
    EF35-105/4.5-5.6    January 1992   A(35) to D(wide open at 105)
    EF35-135/4-5.6      February 1991  B
    EF75-300/4-5.6      August 1992    A(75) to D(300)
    EF50/1.8            February 1991  B
    EF50/1.8II          May 1991       A
    EF28-80/3.5-5.6     July 1992      A (B at 80)
    EF35-350/3.5-5.6USM June 1993      B to D(at 350)
    EF20-35/3.5-4.5USM  October 1993   B
    Interesting Non-Canon Lenses
    Sigma 400/5.6 APO   May 1992       C
    Sigma 21-35/3.5-4.2 February 1992  A
    Sigma 70-210/2.8    May 1993       A+
    Sigma 28-70/2.8     June 1993      B to D(70mm wide open)
    Note however, that the Sigma 400/5.6 actually tested as a 386/6.2. This does not make it a worse lens, but you should be aware of what you are likely to actually get if you buy one. Similarly almost all long lenses and zooms over 200mm are actually significantly shorter (at the long end for zooms) than they are marked. You can consider yourself quite lucky if they are within 5% of the marked focal length, for example the Sigma 70-210/2.8 zoom is actually only 195mm at the long end. This shortfall does not only apply to 3rd party lenses, but to lenses from almost all the major camera manufacturers.

    A much more detailed summary of all the Popular Photography tests on lenses which are available in an EOS mount has been submitted to the FAQ by Leszek Mazur. This summary appears at the end of this FAQ in Appendix D.



    The Sigma 70-210/2.8 (or 70-195/2.8 to be more accurate) does look like a good optical performer at 1/2 the cost of the Canon 80-200/2.8. The following item from "Fotomagazin" submitted by Uli Bodenhausen

    From: uli@i13d5.ira.uka.de (Uli Bodenhausen)
    Subject: f2.8/telezooms tested in Fotomagzin
    Organization: University of Karlsruhe, FRG

    The German Fotomagazin (3/93) tested the f/2.8 AF telezooms. The summary is (without permission):

    Ratings are from 0(bad) - 10(excellent).

    Attention: These results may not be directly comparable to other ratings of other zoom lenses in other Fotomagazin tests. The small print in the test says that the ratings are based on sharpness, contrast, vignetting, flare, distortions and color. They also say that the sharpness measurements allow an equal comparison between all lenses (also in other tests they did). BUT: The contrast ratings are only comparable between lenses with the same opening (f stop). The following results should be directly comparable because all have the same opening. Only one lens of each manufacturer was tested.

    Lens                     rating         rating 
                             optical        mechanical
    Canon AF 80-200          9.2            9.0
    Minolta AF APO 80-200    8.8            8.8
    Nikkor AF ED 80-200      9.6            9.2
    Sigma APO 70-210         9.6            9.2
    Tamron AF LD 70-210      8.8            9.4
    Tokina AF ATX 80-200     9.0            8.8


    The following lenses are mentioned on the net repeatedly for being able to produce good quality images at a reasonable price (maybe this info should go into the EF lens guide???):

    EF 28-70/3.5-4.5 II: This lens boasts an aspherical element to improve its performance when shooting wide open. It is regarded as being one of the best lenses in its focal length and slightly better than the 28-80/3.5-5.6 USM that replaces it. The factors against this lens are: a) the front element rotates, b) the filter threads retract at middle focal lengths, c) the filter size is 52mm rather than the 58mm that Canon seems to now favour, d) they are becoming very scarce. [e) Note that it is now discontinued, so if you want one and you see one for sale, buy it immediately! (RMA)].

    EF 75-300/4-5.6: Optical performance quite good for the money. Main complaints: looks a bit flimsy, not the fastest focusing, no distance scales, and filter threads rotate. It is now available with a USM motor which provides much faster (and quieter) focusing.

    EF 100-300/4.5-5.6 USM: Noted for its fast focusing, it is supposed to be "quite good but not outstanding". The main complaint is that it suffers from "zoom creep".

    EF 100-300/5.6L: This is supposed to be the sharpest lens in its focal length, and the cheapest of the "L"-series zooms (nearly half the price of the 80- 200/2.8L). Main weaknesses are that it has a push-pull zoom mechanism, it's slow focusing, the front element rotates, and the maximum aperture is quite modest. [I have measured better than 80 lp/mm resolution at 300mm wide open (f/5.6) on this lens, which is indeed outstanding performance (RMA)]


  25. What does the "II" mean?
  26. Some lenses carry a designation "II" after the focal length and aperture information. The "II" simply indicates that the lens has the same focal length and aperture specifications as a previous lens.

    Though the 50/1.8 II may be considered "inferior" to the original 50/1.8 (plastic mount, no distance scales), the 28-70/3.5-4.5 II retains the metal mount and distance scales of its predecessor. The 28-70 II is not optically identical to its predecessor and a major change was also the replacement of metal gear components with plastic equivalents. The supposed reason was to increase the smoothness of the focusing and zooming actions. [Anybody have an original 28-70/3.5-4.5 who can comment?]


  27. What about the Tamron 28-200/3.8-5.6?
  28. Here is a review by Robert French:

    From: rfrench@Xenon.Stanford.EDU (Robert S. French)
    Subject: Review of Tamron 28-200/3.8-5.6 AF lens for EOS
    Organization: Computer Science Department, Stanford University.
    Date: Tue, 2 Feb 1993 07:09:00 GMT

    As promised, here is my review of the new Tamron AF 28-200/3.8-5.6 for the Canon EOS.

    First impressions:


    • The lens is very short (approx 3 3/8" at minimum zoom).
    • The lens has a very positive feel to it - the zoom action dial (which is most of the lens body) has a reasonable amount of friction and turns through 45 deg from 28-200mm.
    • The lens appears to be very well constructed. It feels rugged and has a metal mount.
    • The minimum aperture at 28mm is f/22, and at 200mm is f/32.
    • It comes with a bayonet-mounted lens shade that can be reverse-mounted for storage.
    • The freedom of 28-200 zooming is wonderful.


    • The lens weighs a lot more than the claimed 15.2 oz. It feels like it weighs over 20 oz, but I don't have a scale that measures over 16. I don't know why the lens weighs so much more than claimed - the 15.2oz figure is printed on the box and on the info sheet. It takes a little getting used to after using the extra-light Canon 35-70 and 80-200, but it's not bad.
    • There is no focus scale! So much for hyperfocal calculations...
    • The minimum focusing distance is ~7 feet at all focal lengths!
    • The zoom dial turns in the opposite direction from the 35-70 and 80-200, and I find that very confusing.
    • The end of the lens rotates with focusing, so orientation-specific filters will have problems.
    • The focusing motor is fairly slow compared to Canon EF lenses, and very slow compared to USM lenses.
    • At a maximum aperture of 3.8 (which the Canons read as 4.0), the lens is relatively slow at its wide end, but consistent with most zooms on the market at the tele end. This doesn't mean it isn't slow, though.
    • 72 mm filters are expensive.

    After shooting a roll of film (Kodachrome 200):

    The lens appears to perform very well. It appears that the lens shade DOES interfere with 28mm shooting - there is a slight darkening around the edges. There is no visible vignetting at 28mm without the lens shade. The lens also worked well with the Tamron 2x teleconverter. All in all, I like the lens, although it wasn't the perfect lens I thought it was going to be. The long minimum focus distance, slow maximum aperture, and relatively slow focusing motor all make it somewhat annoying. It seems well suited for outdoor photography, although I'm going to keep some other lenses around for inside and special outdoor projects. The 28-200 ability makes much of the problems tolerable, though. I think I'll keep it.


  29. My lens cap is too loose. What can I do?
  30. There are a few solutions:

    a) Buy a "cap keeper" gizmo that strings your cap to your lens. (Most people don't like this idea because it reminds them of "mitten strings"...)

    b) Pop the spring mechanism out of the cap, heat with a hair drier while applying force to mold the ring into the desired shape. An elastic band or two may be useful.

    c) Just screw the cap into the filter threads. My caps stay snugly attached this way!

    d) Buy another (brand) of lens cap! (RMA)


  31. Tell me all about teleconverters!
  32. Canon make two EOS compatible teleconverters, a 1.4x and a 2x. They will only mount on EF telephoto lenses of the "L" series since they have a protruding front element which prevents mechanical coupling to (almost) all the other EF series lenses. Even if you could mount them on other lenses, the results might not be good. The Canon teleconverters are obviously designed to provide an optimum match to the optical characteristics of their telephoto lenses. The Canon teleconverters convey the true aperture of the lens/converter combination to the camera body, i.e. a 300/2.8 with a 1.4x attached to it will show a maximum aperture of f/4 on an EOS body. Both converters can be mounted on any EF series lens if you use an EF25 extension tube. This is, of course, only useful for macro work. To get AF operation with a 1.4x converter you must use a prime lens of f/4 or faster. f/4 will become f/5.6 with the converter attached. Similarly to get AF operation with the 2x converter you must start with a lens that is f/2.8 or faster. f/2.8 will become f/5.6 with the converter attached. With lenses slower than the values specified above the camera will not even TRY to autofocus. Thus unfortunately you cannot get AF operation with the 500/4.5L and a Canon 1.4x converter.

    Tamron, Sigma and Vivitar all make EOS compatible AF teleconverters (there are also a few "store" brands). These converters will mount on any EF series lens, or any 3rd party EOS compatible lens. They do NOT convey the true aperture of the lens/converter combination, i.e. If you start out with a 300/2.8 and add a 3rd party 1.4x converter, the EOS body will still allow you to set an aperture of f/2.8, when your true maximum aperture is f/4. This will not affect exposure accuracy however since the TTL metering will take care of things for you. If you use a hand held meter and transfer readings to the camera in manual exposure mode you will have to remember to make the exposure correction yourself. The only problem I can see is in situations where the lens aperture is used to calculate other things, such as depth of field or flash range. The Tamron 1.4x converter claims to provide AF with any lens faster than f/4.5 (vs f/4 for the Canon 1.4x). I don't know how accurate this is. It certainly seems to work fine with an EF300/4L lens. The Tamron 2x claims to provide AF with any lens of f/4 or faster (vs. f/2.8 for the Canon). This is not really true. It does provide some AF when used with an EF300/4L, but not 100% reliable AF. Under average daylight conditions with average targets it probably gives something like a 65% success rate. The reason Canon's specs are tighter is that they quote numbers where you can expect to rely on AF operation, not that their converters are not as good (they are at least as good, and probably better). From some brief measurements I have made, it looks like both the Canon and Tamron 1.4x converters are indeed very close to 1.4x. The Canon 2x seems to be very close to 2x, but the Tamron 2x seems a little less powerful than stated, perhaps closer to 1.8x. This may not be altogether bad, but it is as well to be aware of it. The difference should give you a little more aperture, but at the expense of a little less focal length.

    Converter quality. Canon's are the best, but also the most expensive. George Lepp (in his "Natural Image" newsletter) tested a number of converters and found the Tamrons to be the best of the 3rd party brands (Tamron, Sigma, Tokina and Vivitar tested with Nikon, Canon and Sigma lenses) most of the time. They were close to the Canon converters in center resolution, but were not as good at the edges of the frame. I have found a similar result comparing images taken with my Tamron converters with those taken by Jay Schlegel using the Canon converters. The biggest difference seems to be between the Tamron 1.4x and Canon 1.4x at the frame edges. Central resolution (used with a Canon EF300/4L) was good in both cases at 70+ lp/mm. However the resolution and lateral color at the edges of the frame were better with the Canon converter. There seemed to be less difference between the Canon and Tamron 2x converters in terms of image quality. Contrast with all the 3rd party converters may also be lower, and they may introduce more chromatic aberration. They cost less than the Canons, so you have to decide if you can put up with the lower quality images, though if you intend to use them with anything other than "L" series telephotos then the Canon converters are not an option anyway. In general, converters don't work well with low cost zoom lenses. They can give acceptable results with some higher quality zooms (e.g. EF80-200/2.8L) and can give quite good results with high quality telephotos, especially if you stick to the 1.4x converters. In general, avoid any 3x converters or "store brand" converters since the quality of images they produce is not likely to be acceptable. Converters are a compromise of size, weight, cost and quality. Only YOU can decide if the quality of the images they provide is acceptable. Do not expect miracles, and do not use them in critical applications (like on a one-in-a-lifetime safari) without testing them on the lenses you will use them with to see if you can live with the results. A converter which gives great results with one lens, may not be all that great with another, so test all the combinations you intend to use.

    One final point, despite anything you may read elsewhere, teleconverters can work no "magic" with respect to depth of field. Whether you have a 400mm f/5.6 lens, or a 200mm f/2.8 with a 2x converter (=400/5.6) you get exactly the same depth of field in each case.


    The following additional information on Canon EF series teleconverters was supplied by Chuck Westfall of Canon:


    Part of the appeal of the EOS system for professional photographers is the availability of EF Extenders for selected EF telephoto lenses. It's easy to understand why extenders are popular: by increasing the focal length of the main lens without significantly increasing its size or weight, they perform a valuable function at a very reasonable price. Equally important, Extenders EF 1.4x and 2x are fully coupled for autoexposure with every compatible lens, and autofocus is possible as long as the maximum aperture of the prime lens/extender combination is at least f/5.6.

    There are certain resemblances between EF Extenders and others with similar specifications. For example, Extender EF 1.4x increases the focal length of the prime lens by 40% and reduces the effective maximum aperture by one f/stop. Extender EF 2x doubles the focal length of the prime lens and reduces the effective maximum aperture by 2 f/stops. But once you get past these similarities, there are several important differences worth knowing about.

    The front elements of Extenders EF 1.4x and 2x protrude about 1/4 inch beyond their lens mounts. This is done intentionally to ensure maximum optical quality with the rear-focus EF telephoto lenses for which they are designed. However, front element protrusion makes it physically impossible to mount these extenders on most other lenses, such as the popular EF 80-200mm f/2.8L. It also prevents "stacking" the extenders.

    EF Extenders have 3 extra communication pins in front to match up with 3 corresponding extra pins on compatible EF lenses. When an EF Extender is attached to a compatible lens, it changes the data transmitted back to the camera body through the lens mount. The changed data includes focal length and effective aperture as well as AF drive speed and focusing movement information. The only noticeable effect of the focal length data is the camera's choice of shutter speed in the camera's program mode; this is designed to reduce the possibility of unintentional camera shake caused by increased magnification. The effective aperture information is relayed to the viewfinder display and LCD panel readouts. Consequently, no conversion is required for the light loss of the extender when using either the EOS exposure control system or an external meter.

    The use of extenders (EF or otherwise) reduces the amount of focusing movement when subject distance changes. A 1.4x extender reduces focusing movement by approximately 25% while a 2x extender reduces it by more than 50%. With a manual focus SLR, this reduction is rarely noticed and easily compensated by observing the sharpness of the image through the viewfinder. However, an autofocus SLR uses computer control to adjust focus. Therefore,the computer "program" must be adjusted in terms of focusing movement, or sensitivity, to compensate for the presence of an extender. The EOS system reduces AF drive speed when an EF Extender is used. The reduction in drive speed directly corresponds to the reduction in focusing movement. As a result, overall AF performance remains unchanged.

    Aftermarket extenders currently on the market with EOS mount do not have extra communication pins. They can only pass the information of the main lens back to the camera. Without the extra pins, focal length and maximum aperture data are not changed, and AF drive speed and focusing sensitivity are not adjusted. Although the camera does not display the effective aperture, in-camera exposure metering remains essentially accurate. In other words, the metering system overcomes the extender's light loss in much the same way as it would compensate for a neutral density filter. More importantly, autofocus may become inaccurate, because the camera tries to extend or retract the focusing system more than necessary.

    Every EOS camera manufactured to date forces manual focus when the maximum aperture display becomes smaller than f/5.6. This is why AF is not supported when the EF 300mm f/4L and 600mm f/4L lenses are used with Extender EF 2x, or when the EF 500mm f/4.5L is used with either EF Extender. When the effective maximum aperture becomes so small that the diameter of the light cone it projects on the AF sensor fails to cover the length of the array, the accuracy of the AF system cannot be guaranteed. It's not a matter of light intensity, but rather of physical dimensions. This comes into play with aftermarket extenders when they reduce the effective maximum aperture below f/5.6, but don't change the viewfinder or LCD panel aperture display.

  33. Is the Tamron TC officially endorsed by Canon?
  34. There have been rumours on rec.photo about the Tamron AF TC being officially endorsed by Canon. Canon endorses no 3rd-party products.


  35. My lens pulls its filter threads inside the lens barrel and/or the filter threads turn during focusing. How can I use a circular polarizer?
  36. Some of Canon's earlier wide angle to short-telephoto EF zoom lenses retracted the filter threads into the lens barrel at middle focal lengths. The most popular examples of lenses with this problem are the: 35-70/3.5-4.5, 28-70/3.5-4.5, and 28-80/3.5-5.6. This can make it difficult to turn the polarizer. In addition, the filter threads on these lenses turn during focusing. The only current lens with this characteristic is the 28-80/3.5-5.6.

    The most important thing is to make sure that the filter you buy fits inside the lens barrel. Avoid circular polarizers with little knobs and other protrusions. If you explain your situation, most retail stores will allow you to test the fit of a filter on your lens.

    If the filter threads turn during focus, focus first, orient the polarizer to taste, then take the shot.

    If you are lucky, the filter ring will extend far enough forward to allow you to turn the filter. There probably won't be much extrusion, so care must be exercised to avoid getting fingerprints on the filter. If there is no way to reach the filter ring, you can set the lens to one of the extreme focal lengths so that the filter ring is accessible, set the polarizer, and then reset the focal length.

    It may be worth trying extending the filter ring with a skylight filter, or, better yet, just a filter ring. Cokin sells "extension rings" for this very purpose of mounting filters on lenses with retracting threads. CAUTION: This may cause image vignetting (dark corners). To get the polariser outside a 28-70II lens set at 28mm you need two filter rings. Even using a 62mm filter (via a 62 -> 52mm adaptor) there is slight vignetting. The 28-70II is a very, very good lens optically, but a real pig to use with a polarizer!

    Alternatively, many larger camera stores have old filters for under $1. Try to remove the filter element by popping the spring, or simply smashing out the glass (with eye protection, of course). Make sure not to deform the filter ring. Examine the corners of your negatives for vignetting at short focal lengths.


  37. How can I use a rubber lens hood if my front filter threads retract?
  38. You're not supposed to. Canon makes specially-matched hoods that clip on the outside of the lens barrel, or mount in a bayonet fashion. This leaves the filter threads free for filters. Read the specification sheet that comes with the lens to determine how many filters are can be installed on your lens without vignetting.

    Since the lenses with this problem are lenses with a wide-angle end anyway, a lens hood probably won't help much with flare anyway (though purists use lens hoods with 20mm lenses, so you be the judge).

    The type of hood required is listed on the sheet and printed on the outside of the packaging, so you don't have to open the box to figure out what hood you need.

    Some "clip-on" hoods, after a bit of "working-in" will simply attach to the lens by being pushed straight on. This saves the hassle of finding where the clip release buttons are.


  39. What are TS-E lenses?
  40. The "TS-E" designation is for "Tilt and Shift for EOS". These lenses have, to a limited degree, movements like that of a view camera. In particular, they can be tilted and shifted relative to the film plane. Without getting into view-camera specifics, let it just be said that this kind of lens is popular for use in architectural photography because the shift allows for the correction of "converging verticals" in shooting situations that do not allow one to get a better angle from which to photograph a building. They are also useful for taking pictures of mirrored objects. The tilt feature allows the adjustment of the plane of focus so that it is not parrallel to the film plane. This is useful in situations such as photographing a field of flowers, where you want both near and distant flowers in focus, but you do not want to stop the lens down to a small aperture. For a full explanation of the tilt and shift features you should really get the "TS-E" brochure (see section 1.1).

    Current TS-E lenses are all manual focus. There main reason is that the AF system assumes that the plane of focus is parallel to the film plane. When a lens is tilted, this is no longer true and can confuse the AF system. [It might still be nice to have AF when no movements are involved though...]

    See the "EF Lenses" and "TS-E Lenses" brochures for more details.


  41. Why are TS-E lenses so expensive?
  42. Because of the movements, the image circle must be larger so that tilting the lens still puts an image on the film. This involves more glass. In addition, there are many more moving parts. Finally, these are specialty lenses that are not in large-scale production.


  43. Why should I use an EOS-1 with TS-E lenses?
  44. Certain combinations of tilt and shift will still move the limit of the image circle onto the film plane. Since the EOS-1 features a 100% viewfinder, it is easy to determine when this has occurred. The EOS 1 can also take a grid focusing screen which is very useful when adjusting the shift of the lens to get parallel verticals.


  45. How much magnification can I get using EOS lenses?
  46. For Canon EF series lenses used with the EF25 extension tube and close up filters, see the Canon Close-up System booklet mentioned in section 1.1. This has a complete set of tables for all the current Canon EF lenses.

    With regard to some non-Canon lenses and accesories: Bob French has submitted a summary of his measurements of the close up performance of the following system:

    EF 35-70/3.5-4.5 (macro) EF 80-200/4.5-5.6 Tamron 28-200/3.8-5.6 Tamron 2X EF25 extension tube

    His data tables are given in Appendix G.


    Panos Tsirigotis has supplied the following information on close up lenses From: Panos Tsirigotis
    Organization: University of Colorado, Boulder

    [With regard to the Canon close up filters CU240 (52mm), CU450 (52mm) and CU500T (58mm) and Nikon's 3T, 4T, 5T and 6T close up filters].

    The numbers on the filters are the maximum focusing distance when you put them in front of any lens. In terms of diopter power, I read in the Natural Image (Spring 1987) an article by John Shaw where he says that this max. distance is "roughly one meter divided by the diopter power of the close-up lens". From this, one can calculate the diopter power of the Canon close-ups: Note that greater numbers imply less magnification.

    CU240 : 4.16 diopters
    CU450 : 2.22 diopters
    CU500T: 2 diopters

    About the Nikons :

    52mm - 3T, 5T: 1.5 diopters
    62mm - 4T, 6T: 3 diopters [actually 2.9]

    The following magnification numbers are from the EOS Close-Up System brochure (Lens + CU500T).

    100-300L @100 @infinity: 0.20X
    100-300L @100 @min.dist.: 0.31X
    100-300L @300 @infinity: 0.59X
    100-300L @300 @min. dist.: 0.98X
    100-300USM @100 @infinity: 0.21X
    100-300USM @100 @min.dist.: 0.28X
    100-300USM @300 @infinity: 0.58X
    100-300USM @300 @min. dist.: 0.91X

    Interesting side-note: since the magnification factors at infinity are not the same it is easy to see that the USM lens is longer at 100 and shorter at 300.

    Panos Tsirigotis, CS grad Email: panos@cs.colorado.edu


  47. What is a good, fast, cheap, small, light telephoto lens for an EOS camera?
  48. Well, these terms are somewhat mutually exclusive. "Good and fast" don't really go with "cheap, small and light". It also depends on what you mean by "telephoto".

    If 300mm is long enough then a number of zooms cover that range. The 100-300/5.6 USM is not a bad lens for about $250. The 100-300/5.6L is better, especially wide open at 300mm, in fact it is probably the best 300/5.6 available. It will cost you around $500. To save some money you could go with the Sigma 75-300 APO lens (about $300), but you lose the very nice USM focusing of the Canon 100-300USM and you may not gain much optical improvement. The Canon 300/4L USM is a very good lens, but at around $900 cannot be called "cheap". It will work well with a 1.4x converter (Canon or Tamron), and give passable images even with the 2x converters. The Canon 300/2.8L is even better and also works very well with the 1.4x and 2x converters (with full AF performance to boot!), but at $3300+ it is no-one's idea of cheap. Sigma have a 300/2.8 APO lens at around $2000+, but it is not as sharp as the Canon.

    If you need 400mm you have a few choices., The Sigma 400/5.6 APO has a good reputation as a lens which delivers value for money (about $450). It is not the world's sharpest or best built lens, but it is capable of yielding good images, even wide open (6.5 on Lepp's scale, see section 4.12). Tokina have a new 400/5.6 apochromatic lens out, but I have not seen any tests on it yet (6/93). I doubt it will outperform the Sigma, but who knows? Canon have announced a new EF400/5.6L lens which I expect to be an excellent performer. The price is around $1400 (discount 9/93). If you are prepared to use stop down metering and manual focus only, the Tamron 400/4 can be fitted to any EOS camera using the Tamron Adaptall mount for EOS. It is a very sharp lens and will cost you about $1800. Again not cheap. Finally there is the Canon EF400/2.8L. A very good, very big, very heavy lens at a price of $5700. Not really an option for most of us.

    So you want a 500? Well, the Sigma 500/7.2 APO is available in an EOS mount (ca. $450). It's not a spectacular performer (see Lepp's numbers in 4.12), but might be OK for some users and it is the only "affordable" AF 500mm lens for EOS. You can use the Tamron 500/8 mirror lens with an EOS Adaptall mount (ca. $325). It is very small and light. However, like most mirror lenses it is slow (actually about 1/2 stop slower than f/8) and not very sharp. It is probably similar to the Sigma 500/7.2 in terms of optical performance, but you can't stop the mirror lens down to sharpen things up like you can with the Sigma, and starting out at around f/9.5 you probably wouldn't want to anyway. Celestron (a telescope maker) has a 500/5.6 mirror lens. Not as small or light as the 500/8s, but a stop faster. It may give usable images, but I would not expect any higher intrinsic image quality than the 500/8 mirror lenses. It may be an option for some people at around $350. Again Canon have a very good 500mm, the EF500/4.5L, but it is not cheap at ca. $4800. Sigma also make a 500/4.5 APO, but it is $3000+ and is not as sharp as the Canon.

    More than 500mm? Are you sure? Well Canon have a nice 600/4L at only $6500. A very, very nice lens indeed, but big, heavy and expensive. You can also use the 300/2.8L with a 2x to give you 600/5.6 with AF and fairly good performance, but that combination will cost you $3500+. Similarly you could use the Canon EF400/2.8L with teleconverters. Sigma have a 1000/8 APO at $3000+, but 1000mm is very long and not something most photographers could use and expect good results. Canon also have a 1200/5.6L, available by special order. This lens is more than big, heavy and expensive - it is very big, very heavy and very expensive (with a rumored list price in excess of $60,000!). Sigma have an inexpensive manual focus 600/8 mirror lens in an EOS mount which might meet some people's needs. Again, mirror lenses have drawbacks, so be warned.

    Telescopes. Can you use a telescope and expect good results? The short answer is NO. The longer answer is yes, maybe, but... Very few telescopes yield reasonable quality images. In general they are too slow and their focal lengths are too long. The longer the focal length the steadier you have to hold the lens and the more atmospheric effects will degrade the image. The only telescopes capable of yielding high quality images (comparable to the better telephoto lenses) are the fast, short focal length, apochromatic refractors. For example TeleVue make a 500mm f/5 apochromatic telescope using Fluorite lens elements. It makes a very good lens (manual focus, fixed aperture), but costs $1700, weighs 10lbs+ and is about 36" long. It is not easy, but it is possible, to use it in the field if you have a good tripod. Its performance as a lens will be right up there with the best telephotos, like the Canon 500/4.5L, but you have no AF, you can't stop it down and it's big heavy and awkward. There are a few other similar telescopes from TeleVue and Astrophysics, but they are not cheap, or light or small, though they are good. None is faster than f/5.

    To sum up, the best, cheapest all round telephoto is probably the Sigma 400/5.6 APO if you can live with the sharpness it gives, which may be perfectly OK for many users. If you need higher performance then you may have to go for the Canon 400/5.6L (assuming it tests well), or the Canon 300/4L if you can live with 300mm and twice the cost of the Sigma. You can put doublers on shorter, cheaper, lenses, but you will end up with images less sharp than the Sigma. Also consider the EF100-300/5.6L, or if you can live with a little less sharpness, the 100-300USM. Both are a little slow (f/5.6) at 300mm but can give good results (particularly the "L" lens).

    [The above opinions are mine, and may of course be wrong. They are only opinions - RMA]

  49. Brief review of the Sigma 21-35 for EOS
  50. I have run a few tests on the Sigma 21-35 zoom lens on an EOS Elan body. The lens is quite large, with a non-detachable lens hood. The front element rotates, so there are the usual problems with polarizing filters (77mm). It seems to be well built (metal, not plastic). Comes with a hard case & strap.

    Resolution was very good at all focal lengths at f/11. Using Elite 100 film, better than 85 lp/mm were measured in the center of the field and better than 60 lp/mm at the edges. At small apertures (f/22) all the numbers were worse due to diffraction effects (as they would be in all lenses). Wide open resolution was suprisingly good, slightly worse than at f/11, but not by much. All in all a very good optical performer.

    Slight lateral color was observed at the edges of the image at all focal lengths, with best performance at 35mm. At all other focal lengths, lateral color was similar. The degree of color fringing was not excessive, no more tha would be expected for a lens of this type and not really observable below about a 10x magnification. Fairly good performance. There was detectable barrel distortion at all focal lengths, again typical for a lens of this type

    AF was accurate at all focal lengths from 24mm to 35mm, but was a bit off at 21mm. The lens is a true zoom, so for best focusing at 21mm it is better to zoom out to 35, focus there, and then zoom back to 21mm (don't forget to disable AF before shooting, or the lens will refocus!). This behavior has been reported in a second lens sample, so it may be a common problem. It is easy to spot. Focus at 35mm on something about 3 meters distant. See what the distance scale on the lens reads. Now zoom out to 21mm and AF again. If the lens shifts focus, something is wrong. At small apertures, depth of field may help minimize the effect of the focus error, but don't bet on it.

    My tests are consistant with the Feb 1992 test in Popular photography. It is a very good lens. There is now a low cost Canon 20-35 USM lens (ca. $450) which should also be considered. It may be mechanically better (USM motor, non rotating front element) and I doubt it will have the focus problem at 21mm that I see in the Sigma lens I tested. It costs more then the Sigma (ca. $340) but it may be worth the difference. There is a Pop Photog test in the Oct 1993 issue.

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