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Old Feb 10, 2005, 11:55 AM   #1
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OK so here's a little MTF challenge for you all.

I have cropped a couple of MTF charts down to 15mm from centre (because that's the only bit relevant to the APS sensors). They're both wide angle zooms.

Question 1:
Which lens shows superior performance with respect to those parameters measured by MTF charts?

Question 2:
Which lenses do you think lens A & B are?

If you know which lens is which because you've seen the charts already then please don't spoil part 2. :-)
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Old Feb 10, 2005, 12:05 PM   #2
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I won't... but we all know what they say about MTF charts!
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Old Feb 10, 2005, 1:30 PM   #3
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Hmm, I think perhaps the challenge was too broad..

I don't want to give the game away so, let's just say that the wide end of both lenses is between 16mm and 28mm. That should narrow it down a bit without making it too easy.

Oh yes and both are Canon lenses, I'm not sure it's fair to compare charts from different manufacturers.

NHL - still think you know the answer?
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Old Feb 10, 2005, 2:01 PM   #4
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Yes - but IMO only the left charts should be compared, with the right charts: one tele is twice the range of the other and it's like apple and orange comparison there, plus that's a pretty good MTF considering the 2nd one is an 'L'!

The 2nd lens(B) is really intended to be used as a super wide on a full frame... while the 1st lens(A) is more optimized to be a tele (which is pefectly matched for cropped dSLRs for example) :?

If you have a 300D/10D or 20D, the better choice would be lens A, beside it has IS to boot :-)
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Old Feb 12, 2005, 3:55 AM   #5
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I posted these because frankly when I saw the two charts it went against everything I had been led to expect from reading these forums.

OK so as everyone probably knows Lens A is the EF-S 17-85mm and Lens B is the 17-40 L.

So what's my point?

That the 17-40L isn't a good lens? Certainly not - it's a fantastic lens.

That the 17-85 is a good lens? Yes, and that claims like "optically you'd be much better off with a real L lens like the 17-40" are just so much bunkum.

You may well be better off with the L, but that will be because it's full-frame, the build quality is better, it suffers less from CA and vignetting @ 17mm, etc. But not because it's sharper.

Sometimes people see what they want to or expect to see. It seems inconceivable that a non-L lens could compete optically, so that's what they end up seeing, even when there is good evidence to the contrary.

Another point is that there really is benefit to be gained from lenses optimised for the smaller sensor. Anyone care to wager what you'd have to pay to get an MTF chart like that covering 17-85mm for a full frame? And if you did is there any doubt that they would put a red ring on it?
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Old Feb 12, 2005, 7:38 AM   #6
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peripatetic

I like your chain of thought from the very first "Cunningly Original..." posting.

You have to remember too that the 17-85 is a brand new lens announced with the 20D... Most posters here had the 28-135 as their general purpose lens before this, and carry it over; So their choice were limited to the 17-40 for the wide angle, hence the familiarity and recommendations!

Also some folks made their purchase with the anticipation of moving up to a full frame in the future, and the 17-85 would limit this potential... It's really up to each camera's owner and their plan, but the point is made: one should not get blinded by the 'L', there are other practical alternatives...
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Old Apr 18, 2005, 7:16 PM   #7
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At around what focal length does the 17-85 switch to F5.6 from F4.0?

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Old Apr 18, 2005, 10:11 PM   #8
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The 17-85 changes from 4.0 to 4.5 at 24mm, 5.0 at 35mm and 5.6 at 50mm. Interesting that I stumbled on the post. I have a 17-40L and a 70-200L and was looking for something to fill in the gap. I was almost decided on a Tamron 28-75 f/2.8 when my local camera shop salesman suggested the 17-85. I took numerous comparison shots with the 17-85 and my 17-40L. I have to admit I can see very little difference in sharpness, color and contrast. I purchased the 17-85 with assurance from the salesman that I could bring it back if not satisfied. I've been comparing the two for the last three days. The 17-85 may be a little (and I mean little) less sharp on the edges when wide open. Obviously there's no comparison beyond 40mm. I think I can easily sell the 17-40L and be happy with this one lens solution from 17-85mm. The IS is also a nice feature. This lens up to 2/3 of stop slower than the 17-40 but the IS helps to compensate and on a 20D, a higher ISO is always a reasonable option.
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Old Apr 19, 2005, 7:13 PM   #9
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Humrme,

Thanks, exactly what I wanted to know!

I have the 17-40L and 24-70L. Another thread is comparing the 24-70 to the 17-85 if you're interested. See: http://www.stevesforums.com/forums/v...291840#p291840

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Old Apr 20, 2005, 5:15 PM   #10
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NHL,

You wrote :

Also some folks made their purchase with the anticipation of moving up to a full frame in the future, and the 17-85 would limit this potential...



Supposing that in a couple of years, there would be a full frame DSLR for 1000-1300$ (or equivalent to 350D or 20D of today), than the 17-40 L would be much sharper in the wide area than the 17-85 ?
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