Another 100-400 Sharpness question.

Started Sep 21, 2009 | Discussions thread
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GoldenSpark Senior Member • Posts: 1,037
Another 100-400 Sharpness question.

I've been using my recently acquired (older) 100-400 on a 50D and also a 30D.
As I think is usual, I started off finding it hard to get good results.

I persevered using good advice from this and other forums, and have been getting better results.

BUT, there seems to be conflicting stories about sharp vs. soft copies of this lens.

Many of the sharp shots I have seen are in good light stopped down to f/8-11, and then are usually "published for Web" at quite low resolution, so look sharp but are in fact very pixelated. I've seen plenty of softer shots wide open at 400mm (f/5.6), often 100% crops. There are a few people claiming copies that are almost as sharp wide open as stopped down, but again these are usually low resolution images.

What I find with mine is that for subjects close to, I can get shots at f/5.6 that are almost as sharp as those at f/11. But nearer to infinity it is always sharper at f/11. The f/5.6 shots are definitely softer.
Prints show the same story. Close subjects are good, distant subjects less so.

The question is, how normal is this?

The MTF data published on this lens seem to suggest the lens will always be softer 400mm @f/5.6 compared to f/8-11, I'm just not sure how much in real world situations. I am still a little skeptical of the claims about sharp at f/5.6. I have done tests with a homemade chart that suggest about 1600 lw/ph at 400mm f/5.6 under best conditions, so maybe this is normal. The MTF suggests this.
Any comments?

I really want to decide whether I still have to improve my technique, or if the lens does need calibration.
(I've done loads of focus tests, so I know where I am with that variable!)

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