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 on: February 04, 2016, 12:49:27 PM 
Started by KeithB - Last post by Bob Atkins
I just tried it with some images I recently shot with a 50/1.8. I'd shot these test images of a resolution chart at various apertures for testing out some software, so I was ready to go!

My conclusion is that, as I suspected, it can't and doesn't remove diffraction effects. It just ads a bit of sharpening. Shots at f22 with "digital image optimization" showed lower resolution than uncorrected shots at f16, which in turn showed lower resolution that f11 etc.  f4 is the sharpest aperture of this lens, with or without digital image optimization applied. At f4 without DIO it's sharper than at any other aperture with DIO and much, much sharper than at f16 with DIO.

You can't get around diffraction. There's just no way. If there was, astronomers wouldn't have to build bigger and bigger telescopes to see more detail on bright objects. A tiny backyard 4" reflecting telescope would resolve as much detail on a bright object, like the moon or mars, as the largest telescope in existence. It doesn't work that way.

Digital image optimization is just a fancy term for a process that corrects as many of the image aberrations as possible and ads a bit of sharpening to try to mitigate the effects of diffraction softening, but the effect on resolution is minimal.

Why do Canon talk about diffraction? Probably a mixture of marketing hype and Japanese-English translation!

 on: February 04, 2016, 12:14:42 PM 
Started by KeithB - Last post by Bob Atkins
I've not tried it but I will take a look at it if I can find the download.

I'm not sure it can actually correct for diffraction though. You really can't correct for diffraction. Maybe they mean something else, or maybe they just mean they add some sharpening.

Unlike distortion or CA, which distort the information in an image, diffraction reduces the information. You can correct for distortion and CA by "undistorting" the information, but you can't put back information that isn't there in the fist place. Diffraction reduces resolution and you can't get it back. You can sharpen the image to make it LOOK sharper and you can even try to guess at what the missing information might be based on some sort of estimation function, but it's just a guess. The fact that they say you need to set sharpening back to "0" before using digital lens optimization suggests that sharpening is involved.

 on: February 03, 2016, 09:05:25 AM 
Started by KeithB - Last post by KeithB
Also to bring out the fact that this correction is now built into the 1DX Mk2.

 on: February 02, 2016, 01:38:52 PM 
Started by KeithB - Last post by KeithB
I was perusing the manual for DPP 4 and came across the "Digital Lens Optimizer" function which
This function enables the resolution of images to be increased by
removing any remaining aberration related to image-forming capability
or any deterioration of resolution resulting from diffraction phenomena.

You actually have to download the correction data to do this. I assume it does a convolution of the data with the theoretical MTF data.
Has anyone tried it? Bob, where do you think it might actually help?

 on: January 17, 2016, 11:33:28 AM 
Started by bmpress - Last post by Bob Atkins
I see no reason why it wouldn't. I have an old Tamron 1.4x myself and it words fine with my 6D, 7D and 70D as well as all my Canon and 3rd party lenses. The optics are slightly smaller, so I think there's more vignetting when used with long telephotos on a full frame camera. I've had good luck with my Tamron 1.4x on a Canon 500/4.5L and even get AF with bodies that don't support AF slower than f5.6. I don't think it slows down AF like the Canon TCs do, which has resulted in it "hunting" for focus under some conditions where the Canon 1.4x had no trouble. The Canon TCs do slow down focus for more reliable AF.

Adorama gave a couple of used 7D MkII bodies. Don't know how their prices compare with an
EOS 7D MkII on eBay
for items of the same age/cendition, but you do get a 90 day warranty and a 30 day "no questions asked" return policy, something you don't usually get form a private sale. The EX+ one at $999 sounds like a decent deal. If I didn't already have too many DSLR bodies, I might be tempted myself! Maybe if I sold my 7D MkI...........

 on: January 16, 2016, 08:26:41 AM 
Started by bmpress - Last post by bmpress
Thanks for your analysis, Bob. I am going to find a used 7d II.

But as a follow-up question, will an old Tamron 1.4 Extender work with my 5d iii and 100-400 II?

 on: January 15, 2016, 05:23:23 PM 
Started by bmpress - Last post by Bob Atkins
Given that you have the 5D MkIII and 100-400, your cheapest and lightest route to a longer lens is an extender like the Canon 1.4x. That will still give you AF (with the center focus zone) at f8 and you'll be at 540mm at full zoom.

You can get a used MkI  for under $100 or a used MkII for under $200 from Adorama.  A new MkIII extender will cost you $429 .

However looked without regard for you current gear, and assuming you wanted maximum reach, I'd have suggested anEOS 7D MkI or EOS 70D and a Sigma or Tamron 150-600/5-6.3. Probably the Sigma because it will take the Canon TCs (using Live View AF or MF). Useful for perched birds, not birds in flight!

With your current setup you could still go with an APSC body if the cost and weight aren't prohibitive. I'd go that route over the 5D MkIII and TC since you'll have better AF, more AF points and be at an effective 640mm f5.6. A little more noise maybe if you're shooting at high ISO but I think the images would likely be better than using the 1.4x on the 5D MkII, and with the 5D MkII you can still use the 1.4x TC and get center zone AF at an effective 896mm f8. If the weight is too much, you could always leave the 5D MkIII at home if you know you're mainly going to be doing long telephoto shots!

You can get a 7D MkII (open box) for $1250 ir a new one for $1500  or a 70D from $799

It's generally true that an APSC body will be better than an Full frame body + TC for long telephoto readch, assuming that low noise at higher ISO settings isn't the deciding factor.

So my kit for telephoto shots of small subjects would probably be the 7D MkII, a Sigma 150-600 - and a used MkI or Mkll 14x TC for when my subject was sitting still!

The one advantage of the Canon 100-400 MkII is that the AF may be faster and more accurate when tracking birds in flight than a 3rd party lens. But I'd still put it on a 7D MkII.

A lightweight Rebel body is also an option, but you're out of luck if you demand AF microadjust. The 70D has it, but none of the rebels be. The Sigam 150-600 has it though, via the Sigma USB Dock (see

There are so many options here, it's hard to pick one, but going back to my opening comment, with the gear you have, I'd go with a used Canon 1.4x TC and soo how that works out. It's light and it's relatively cheap. If it doesn't do the job, then you can consider other options.

 on: January 15, 2016, 09:18:36 AM 
Started by bmpress - Last post by bmpress
Good point...thanks.

 on: January 14, 2016, 02:29:42 PM 
Started by bmpress - Last post by KeithB
I don't know whether you use it, but the Rebels do not have focus micro-adjustment, which I would think would be important to a birder.

 on: January 14, 2016, 09:55:10 AM 
Started by bmpress - Last post by bmpress
Hi Bob,

So now I have 5d III and 100-400 ii.... I gave up my Tamron 150-600 as it was too heavy.

The question is what to do about shooting birds. Would you suggest an extender over a second APC body and if not, then which body to get?

I looked at the Rebels and liked their weight. The 70d seems much better, but then again, it is heavier and costly. In fact it is not much less than a 7d ii in price.

Glad you are back in the saddle...



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