One of the disadvantages of small sensor APS-C Digital SLRs (basically everything but the Canon 1D and 1Ds series cameras) is that the 1.6x "multiplier/crop" factor makes all your existing 35mm wideangle lenses into "not so wide" angle lenses. Nikon cameras are slightly better, with a 1.5x "multiplier/crop", but still basically suffer from the same problem. On a 40D/50D or Digital Rebel XSi/XTi your 24mm lens has the same field of view as a 38mm lens would have on a full frame camera. Your wide 20mm becomes a moderate 32mm and even your superwide 16-35 zoom becomes a mid-range 26-56 lens. Even the widest rectilinear prime lens you can get for 35mm a 14mm - turns into only a 22.5mm lens.
So what can you do? Well , you have to turn to one of the new ultrawide zooms made specifically for small (APS-C) sensor digital cameras. Last year there were one of two, this year there are five, so things are getting a little better! There is one other alternative, and that's to use a fisheye lens, and I'll deal with that later.
For now here is a comparison of the Ultrawide zooms available for the 20D/30D/40D/50D and Digital Rebel series cameras:
|Coverage||Mount||Weight||Length/Diam||Street Price (est.)|
|Tamron AF 10-24/3.5-4.5||APS-C||EF||406g||99.1mm/78.7mm||$500|
|Sigma 12-24/4.5-5.6||Full frame 35mm||EF||615g||100mm/87mm||$690|
The following table shows the 35mm full frame equivalent focal length (in terms of fiedl of view) for lenses from 10mm to 24mm on an APS-C DSLR.
Though the wide end of these lenses only differ by 1 or 2 mm, at these focal lengths that does make quite a difference in terms of angle of view and field of view as the following table shows
|Lens focal length||10mm||11mm||12mm|
|APS-C Horizontal angle of view||96.7 degrees||91.3 degrees||86.3 degrees|
|APS-C Horizontal field of view at 100ft||225ft||204ft||187ft|
|The Tamron 11-18/3.5-5.6 is wider than the Tokina 12-24/4 or Sigma 12-24/4.5-5.6 at the wide end of the range and it is also faster. It's the smallest and lightest of the 4 lenses and second least expensive. In the review section of this website up can find a full, hands-on, test of the Tamron 11-18/3.5-5.6. This lens has now been replaced by the 10-24/3.5-4.5 (see below), which is probably a better buy.|
|The Tamron 10-24/3.5-4.5 Has the widest range of any of the superwide zooms. This lens not only has a wider zoom range than Tamron's original 11-18/3.5-5.6, but it's faster and cheaper than that lens was originally, so it's a winner on all counts! As of November 2008, this lens isn't widely shipping yet, but you can check current stock situation at ADORAMA via this link|
|The Tokina 11-16/2.8 is the fastest of all the superwide zooms for crop sensor cameras. It's a constant f2.8 which makes it up to a stop faster then all the others at 16mm. The downside is that the zoom range is somewhat limited. By limiting the zoom range though, Tokina have kept the price and size low. If you really need a fast wideangle, this is the one to get (in fact it's your only choice!). For most work (landscapes etc.) I think I'd rather have a wider zoom lens and live with a slower lens myself.|
|The Tokina 12-24/4 has a wider zoom range than the Tamron 11-18/3.5-5.6 and, at a constant f4, is slighly faster then the f4.5 lenses. However it's "only" 12mm at the wide end (vs. 11mm for the Tamron 11-18/3.5-5.6 and 10mm for the Canon 10-22/3.5-4.5, Tamron 10-24/3.5-4.5 and Sigma 10-20/4-5.6). It's the least expensive but it's almost as heavy as the Sigma 12-24/4.5-5.6.|
|The Canon 10-22/3.5-4.5 is the widest lens of all and has the 2nd widest zoom range (2.1x), though it's also the most expensive. Being an EF-S lens it can't be mounted on a full frame body. The Tamron, Sigma and Tokina lenses can be used on all EOS bodies, but they will vignette at the wide end of the range. The Canon 10-22/3.5-4.5 has a USM motor with full time manual focus. Optical quality is excellent. See my hands-on review of the EF-S 10-22 for more details|
|The Sigma 12-24/4.5-5.6 is the only lens with full frame 35mm coverage. However it's the heaviest of all four lenses and the second most expensive. The full frame coverage means the hood is designed for 35mm, and so won't be optimal when used with an APS-C sensor body. It also takes rear mounted gel filters (the other 4 lenses take 77mm screw in front filters). Incidentally 12mm is the widest rectilinear lens made by anyone for full frame 35mm use.|
|The Sigma 10-20/4-5.6 is the widest lens (along with the Canon) and the leat expensive along with the Tamron 12-24/4. It doesn't zoom as far as the Sigma 12-24/4.5-5.6, the Canon 10-22 or the Tokina 12-24/4 and it's a little heavier than the Canon 10-22/3.5-4.5 and Tamron 11-18/3.5-5.6.|
Which of these superwide zooms is best for you depends somewhat on what you shoot, whether weight is an important factor and how much you want to spend. If you shoot both APS-C digital and 1.3x and/or full frame film or digital, then the Sigma 12-24/4.5-5.6 lens has a lot of appeal since it's the only one with full frame coverage. The Canon is nice (USM, FTM) and wide - but expensive and EF-S mount only. The new Tamron 10-24 looks very interesting, having a slightly wider range than the Canon 10-22, but being almost $200 cheaper. As I write this (11/08) I haven't had a chance to try one out yet, but it sounds like a good lens. The Sigma 10-20/4-5.6 is wide and the least expensive, but a little heavier than two of the others.
So what about the fisheyes.....see part II of this article!
Next: Part II - Fisheye Lenses