How objective lens MTF test at Photodo photo news

[roberto_watson_garcia]

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?

[jay_.]

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.

[silverfish1]

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.

[albert_smith]

Roberto,

 

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I am including an interesting article about lens testing I got from

Steve Gandy's site. Take a look at the following address:

 

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

 

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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.

 

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

[andrew_schank]

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.