photozone has been posting MTF50 data in the center and borders. It would be nice to see MTF25, MTF75 or other values from several spots across the frame:
MTF curves are never linear. If you just look at MTF curves released by manufacturers, sometimes the curve drops off dramatically at the border, while other times, it drops off gradually. In the first case, image quality only on the borders would be compromised. In the latter case, image quality woud suffer across the frame. Also, the choice of "50%" from the explanation on imatest is a bit dubious and ad hoc. The author mentions something about printers... MTF 25 or something close to it could tell us about "resolution" as in the ability to *resolve* detail, while MTF 75 or something close could tell us about "overall contrast." Note that the graph with MTF on the y-axis and LW/PH on the x-axis is also never quite linear. Thus, the MTF50 numbers don't tell us the whole story.
These are just some words to encourage including *more* charts and data in future reviews...and maybe a fancy Java applet to navigate through this data. <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='
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[quote name='guy_incognito' timestamp='1308082209' post='9210']
photozone has been posting MTF50 data in the center and borders. It would be nice to see MTF25, MTF75 or other values from several spots across the frame:
MTF curves are never linear. If you just look at MTF curves released by manufacturers, sometimes the curve drops off dramatically at the border, while other times, it drops off gradually. In the first case, image quality only on the borders would be compromised. In the latter case, image quality woud suffer across the frame. Also, the choice of "50%" from the explanation on imatest is a bit dubious and ad hoc. The author mentions something about printers... MTF 25 or something close to it could tell us about "resolution" as in the ability to *resolve* detail, while MTF 75 or something close could tell us about "overall contrast." Note that the graph with MTF on the y-axis and LW/PH on the x-axis is also never quite linear. Thus, the MTF50 numbers don't tell us the whole story.
These are just some words to encourage including *more* charts and data in future reviews...and maybe a fancy Java applet to navigate through this data. <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='
' />
[/quote]
+1
This wasn't really an issue in the earlier days when testing was mostly full-frame lenses on APS-C sensors. Nor when even recently when testing 'u'ber-lenses (i.e. Canon L and Zeiss ZE/ZF) on full-frame sensors. They are relatively huge chunks of glass relative to sensor size.
But testing either "typical" compact-prime wide-angles or large range zoom lenses on either full frame (i.e. Nikkor 28/2.8, 24/2.8, Ultron 20/4) or APS-C (i.e.Pentax DA15/4, DA18-135) there is an irrational expectation of performance in the corners.
On lenses with weak corners, I would like to see additional data points included at the golden-triangle intersection.
[quote name='dave9t5' timestamp='1308105115' post='9230']
On lenses with weak corners, I would like to see additional data points included at the golden-triangle intersection.
[/quote]
Hm, didn't we have this discussion already a few weeks ago? Anyway: it won't happen, sorry.
-- Markus
[quote name='mst' timestamp='1308116714' post='9233']
Hm, didn't we have this discussion already a few weeks ago? Anyway: it won't happen, sorry.
-- Markus
[/quote]
What about charts for different MTF values? That should be easy enough.
EDIT: About the "didn't we have this discussion already a few weeks ago". I don't read this forum frequently. Nevertheless, there are very good reasons why there is demand for more thorough testing. slrgear.com seems to do more thorough testing.
[quote name='guy_incognito' timestamp='1308209333' post='9273']
What about charts for different MTF values? That should be easy enough.
EDIT: About the "didn't we have this discussion already a few weeks ago". I don't read this forum frequently. Nevertheless, there are very good reasons why there is demand for more thorough testing. slrgear.com seems to do more thorough testing.
[/quote]
As of now we consider the MTF analysis to be sufficient. Adding further MTF characteristics wouldn't result in a substantial gain of information. At some stage we considered MTF20 charts but this would also make things more complicated and it would only appreciated by a minimal amount of users. There must be a balance between simplicity and substance. This is not a science project but a photo magazine after all.
However, we are looking into other aspects such as a formal glare analysis, contrast and possibly field curvature. IMHO this is all more important than adding more MTF data.
Klaus
First of all: I did not mean to imply one should search the entire forum here before posting a question. I know this is an often posted rant elsewhere, but I was simply having some sort of "deja vu". Sorry if you felt offende, it wasn't meant that way.
Now, regarding your suggestion: we could of course include additional data. However, the more data we add to reviews, the less reviews will happen. That's why we stick to MTF 50. And 3 measurement spots. We want our reviews to remain comparable within each test system.
In addition, we try to keep things as simple as possible, we certainly don't want more than 3 pages per review.
-- Markus
Edit: obviously written at the same time as Klaus' post <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/wink.gif' class='bbc_emoticon' alt='
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Thanks for the responses, guys.
I remember that whenever substantial, the reviewer noted a drop in contrast at the specific aperture and when that contrast recovers. Also, when contrast is above average, this is also noted in the review. At least for me, this is fair enough, no need for numbers here.
Christian
I consider these tests to be reviews for photographers, not pixel peepers! There is no need for more info to make a decision to buy or not to buy a given lense. Keep at it guys, you are doing a better job than any other site I know and read!
I think that if a person has a real need for more information than what you guys supply, they probably should be doing the testing themselves.