Lens Rentals reviews the 35-100 / 2.8

Started Nov 2, 2012 | Discussions thread
Anders W Forum Pro • Posts: 21,468
Re: Lens Rentals reviews the 35-100 / 2.8

thinkfat wrote:

Anders W wrote:

MTF-50 is chosen precisely because it has been found to correlate best with human perception. You can look at the entire MTF curve if you like and some test sites, e.g., DxOMark, let you do that. If you do, you will find that lenses that do well at MTF-50 also tend to do well at other contrast requirements than 50 percent.

I don't recall exactly, where, but I read a pretty nice article about pinhole lens design (and about how sometimes a bad engineer kicks out a good engineer who happens to not understand the problem). It went to say that it is most important for a lens to have good contrast (i.e. a high MTF value) in low and mid frequencies and even a steep drop-off towards high frequencies will still give the perception of sharp images. Whereas a lens with the MTF value declining steadily across frequency will appear soft even though performing better at high frequencies.

I'm not ready to accept that MTF-50 really models human perception in the best way. To me it's just as likely that it just gives nice curves that are easy to read and compare.

I am not sure myself whether MTF-50 is the best criterion (due to the simple fact that I don't have the real-life examples I would need in order to judge the matter based on my own perceptions). I would also guess that the conclusion depends on things like display size, resolution of the output medium, and viewing distance.

One may of course additionally debate whether a single number (per FL, f-stop, and area of the frame) is sufficient. Seeing the entire MTF-curve (for each of four different distances from the center of the frame), as DxOMark lets you do, is of course more informative.

However, if you start looking at those curves, you will find, as I pointed out in the post to which you replied, that lenses that do well at a contrast requirement of 50 percent as a rule do well even at higher contrast requirements (corresponding to lower frequencies). That's why I am not so concerned about the widespread use of MTF-50. I am pretty sure that using a higher contrast criterion would not yield significantly results in most cases.

Once you get to very low contrast requirements, however, the picture gets more diffuse. If I have understood things correctly, the current MTF-50 practice came about as a better alternative to the old practice of simply counting how many lines you could distinguish no matter how low the contrast, which in practice meant a very low contrast requirement.

For their scoring of lenses, and for the lp/mm values they report unless you start digging, DxOMark, unlike most other sites, uses a contrast criterion as low as 20 percent. Since I am pretty sure that's too low for my perceptual standards, I prefer to look at their MTF curves, where I can choose whatever contrast requirement (or frequency) I wish.

 Anders W's gear list:Anders W's gear list
Panasonic Lumix DMC-G1 Olympus OM-D E-M5 Olympus E-M1 Panasonic Lumix G Vario 14-45mm F3.5-5.6 ASPH OIS Panasonic Lumix G Vario 7-14mm F4 ASPH +28 more
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