I Just been looking at lens MTF test at www.photodo.com, and just want your own coments, also would like to know how is this test done, and if they test the entire format or just the center or an average of this, I felt 50 summicron under rate, specialy when it is the best lens wide open, by a margin. How objective are this tests? And what do they represent?

-- Roberto Watson (mawago@prodigy.net.mx), December 16, 2000

Answers

Look on the Photodo site under "Articles" for a complete description of their test methods, criteria and the way they "weight" the results. As I recall, they only test the lenses at infinity and give more weight to f/8 performance in their "weighted averages" (their rationale as stated, because most lenses perform best at that aperture). So the results say nothing of a lens' close-range performance (where many lenses tend to do worse, while Macros tend to do better) and would seem to penalize lenses optimized for wide-open performance that might reach their peak at f4 or 5.6 and start to decline by f8. I take their "numbers" with a bit of skepticism, not because of bias or inaccuracy, but because they only pinpoint a lens' performance within a narrow range. Of more usefulness to me are the MTF graphs on Photodo. The higher (towards 100%, sharpness and contrast), the straighter (center to corner performance) and more closely aligned the saggital and tangential(solid and dotted lines) curves are (correction of aberrations), the better the overall performance. These graphs are taken at specific apertures (wide open and mid) but again, only at infinity. The Photodo tests aren't perfect but I consider them more reliable than the "authoritative" assessments made by individuals claiming to be doing scientific testing but who never actually present numbered data, only their worded conclusions. And Photodo tests many brands of lenses, not just Leica, which is of more use to more people than just those debating which generation of a particular Leica lens to buy.

-- Jay (infinitydt@aol.com), December 16, 2000.

I realize you are asking about a specific kind of test but I feel compelled to say something about lens tests in general. Side by side comparisons of different lenses under the same conditions and parameters that give center and edge resolution figures for all apertures were more useful to me. Leitz has long maintained that tests of flat field targets are of limited importance since in practice most subjects are 3 dimensional and curved field performance is ultimately the real test of a lens. In the tests I recall from photo publications in the 60's the 50mm Summicron resolved 80 lines per mm at center and edge for f/5.6, f/8, and f/11 but unless you are photographing a newspaper that's misleading. Finally professionals have different needs than artists sometimes. A few "art" photographers have opted for lenses precisely for the peculiar qualities even defects they exhibit because of lack of correction.

-- Michael Johnson (mdjohnsonphoto@hotmail.com), December 16, 2000.

Roberto,

I am including an interesting article about lens testing I got from Steve Gandy's site. Take a look at the following address:

http://www.cameraquest.com/lenstest.htm

I have been burned by trusting general lens testing in magazines. I have also been shocked by negative results for lenses that I have and found to be outstanding. So now for me, the most important lens test is... Do I like the lens? For me, I don't have any Leica lenses that I don't like, (since I got rid of my Summarit), so a lens test telling me that I should not like my lens would be invalid to me. My friends laughed at me when the magazine POPULAR PHOTOGRAPHY rated the Summilux's of the early '90's as average... poor at wide stops. Trusting that magazine, people should have expected better result with a Sigma lens. I don't think too many Leica users traded in their equipment for consumer level zooms from Japan.

Your photos are the only lens test you need to be concerned with.

-- Al Smith (smith58@msn.com), December 16, 2000.

The photodo test remind me of the 0-60 times for cars times printed up in "Road & Track" magazines. It may be an OK bench mark to compare things to one another, but it is certainly not the only consideration you'd need to know if you wanted to know which was "the best" for some reason. Lens quality has a lot of other intangeables, including the now famous "bokeh", resistance to flare, color reproduction, as well as the mechanical build quality of the lens. The other point about any test is that they tested a different lens than the one you will be buying. There are always sample variations from lens to lens, although with Leica optics they should be minor. I've experience significant sample variations in some Nikon lenses I've owned over the years, so I know it does exist. I agree the only test that matters is if you are happy with the results, and of course the lenses and cameras aren't really the things creating the images, we are.

-- Andrew Schank (aschank@flash.net), December 16, 2000.