17-40mm v 20mm

I've just done a quick comparison between my 20mm and my 17-40mm and I'm kinda surprised. At f4, the two are IDENTICAL. But at f16, the 17-40 is clearly better by a noticable amount. Does this make sense? Isn't the fixed supposed to be better than the zoom? Long story short, I may be selling the 20mm soon. Anybody else have experience with this type of thing?

I may do a more scientific test later today and I'll post those results here today or tomorrow.

Never used the Canon 20mm but I've read a couple of reviews that though it was one of the weakest primes in Canon's lineup. If they were accurate then it getting trumped by a decent zoom probably isn't that much of a suprise.

Well, it's unfortunate, because I kinda want that 2.8 for those rare occasions... but then I would rather have good image for the majority of occasions. 16-35, here I come.

I owned the 20 mm f/2.8 for a little while. Nice lens, quick to focus, pretty sharp, but it didn't really have anything that set it apart from the 16-35 at the same focal length. In fact, at f/2.8, its center sharpness was not quite as good as the 16-35. Stopped down, they were much closer though the 20 never got quite the "pop" that the 16-35 has. It isn't a bad lens, by any stretch and if you want a 20 mm lens, it's respectable. Just not excellent.

So what is the deal with Canon wide primes? Why are they all kinda mediocre?

I'm not sure that "mediocre" is quite the right word. Less than excellent would be a good description though.

Well, I would say mediocre. When I buy primes, I expect them to be better than zooms in regards to color, sharpness, etc... When a prime is equal to or worse than a zoom, I kinda feel like WTF? Will I have to go to 3rd part glass to get awesome primes for my Canon? Leica or Zeiss or whatever?

I've got a Zeiss/Jena 20/2.8 sitting here right now. I'm waiting on my focus screen to give it a good test, but my preliminary tests show it to be about on equal footing to the 16-35 as well. It might have some corner advantages, but I really need to give it a fair workout before I make that judgement. I'm starting to think that to get excellent glass wider than 24 mm (on a full-frame), one must turn to Contax/Zeiss or Leica lenses. Of course, they're all quite expensive as well.

On the other hand, if your prints aren't going to be large than 11X14, then most ultrawide lenses are fine.

It is rather odd that the two zooms in that focal range are at least competitive with the prime lens offerings, but the zooms are very new designs - perhaps some of that new design will be applied to a couple of new wide primes some day.

I hope so. I'm now trying to figure out my budget for the 16-35... Sell the 20mm, sell the 17-40, sell the UV and polarizer for the 20mm, that's about 200 less than the price of the 16-35 right there. Now I just need to get $200 and a justification for spending that much on what I basically already have.

This is interesting. I have tests that say the 20mm prime is just a bit sharper than the 17-40 and the 16-35 is
quite a bit less sharp than the 17-40. This fits with the Canon MTF data.

Tests also indicate the prime has lower SA and CA.

Of course once you get above 20mm the primes seem clear winners.

Ref
http://www.popphoto.co​m …/download/57200​310416.pdf
http://www.popphoto.co​m …ad/PP1104_PRIME​vsZOOM.pdf
http://www.the-digital-picture.com …-2.8-USM-Lens-Review.aspx
http://www.wlcastleman​.com/equip/reviews/17-40/index.htm
http://www.wlcastleman​.com/equip/reviews/28m​m/index.htm
http://www.luminous-landscape.com …/lenses/canon-17-40.shtml

The 16-35 and 17-40 are rather similar in performance - My 16-35 had slightly sharper corners at the same apertures compared with my 17-40, which is why I still have the 16-35. I suspect that various copies of each lens might lean one way or the other, given sample variations. Both are top-notch lenses, especially considering that they are ultra-wide zooms. 16 mm is W-I-D-E on a full frame camera!

So Tom - do you currently have both 17-40 and 16-35? Or just the 16-35?

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Just the 16-35. Sold the 17-40, bought and sold a 20/2.8, bought and sold a Sigma 20/1.8, and I've just recently acquired a Zeiss/Jena (not to be confused with the expensive Contax/Zeiss) Flektogon 20/2.8 for testing. The Sigma was a bit disappointing because it had a bit of an uneven sharpness, with the right side softer than the left. A lens element was probably not properly aligned in my copy. The others have performed well, with the primary differences being noticeable with larger apertures.

I wish I had kept my 17-40 a bit longer to test side-by-side with the 16-35 - my limited testing gave an edge to the 16-35 in sharpness towards the corners, but I didn't test for other factors such as flare, color, and contrast.

I had heard that the 17-40 gives comparable performance to all the cheaper Canon primes within it's range. Can't say myself if it's true, but I went with the 17-40. I'd certainly be interested in wide angle primes if they gave superior performance. Someday I'd like the 35L.

This has been reported in this http://wlcastleman.com​/equip/reviews/17-40/index.htm review, in fact the 20mm was a bit better than the 17-40.

I suspect like all the ultra wides it depends on how good a copy you have, that is why opinions vary between the 16-35, 17-40, and 20.