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Thread: 210 APO-Symmar-L

  1. #31

    210 APO-Symmar-L

    "You'll find that it's possible (common, actually) for a lower resolution lens to be sharper than a higher resolution lens." Paul I actually just don't believe that this applies to modern LF optics (which after all is what we are discussing here) - please can you provide some examples or some source material I can go and have a look at.
    Also:

    "Which is why a lens that produces high modulation (contrast) at 5-6 lp/mm (print resolution) but that has a low maximum resolution will appear much sharper than one that resolves many more lines per milimeter, but has lower modulation at 5-6 lp/mm." Can you explain this a little more clearly - Are we talking about contact printing here, or are we making some very huge assumptions about enlargment size. Once again, I've yet to see a modern LF optic which produces low modulation at print resolution (I'm presuming contact print - so no enlargement factor) but whose resolving ability is very high. My experience and (just about everyone else's too) seems to indicate that they are all practically indentical at print resolution (which is just a nothing sort of measure when no enlargement factor is used). I cannot believe that any modern lens is going to appear "much sharper" than any other at print resolution.

    I recently tested 10 modern 150mm lenses to answer my curiosity around which lens would be most suitable for my puposes. I shoot architecture and some landscapes - color and black and white. I was interested in which lens would produce the best print (so there are a whole lot of variables in there). Percieved sharpness and tonal graduations are probably the key factors. Perceived sharpness includes modulation and resolution in a very "layman" kind of way. I shot a test chart and a real world 3-D subject (subject in both B&W and color). I'm aware of the limitations of the test chart. I was going to follow Norman Koren's methodology, but rightly figured that for what I wanted to deduce, the real world subject supported by the test chart would tell me all I needed to know. What did suprise me is that the test target (just the rez bars from the USAF chart shot centrally and with an edge target in the frame) actually produced the same results as the real world subject across the board. Were there significant differences: not really - one of the 10 was quite weak (I'm guessing it was a bit of a lemon lens). The rest would all have produced results which were not discernable in B&W prints under close examination below a 6X enlargement (24X30 from a 4X5 negative). To split hairs on the top 5, you would need very big enlargements (over 10X). Basically, this really validated Kerry and Chris' testing for me in a real sense - what is contained therein needs understanding in it's application, but it is an extremely useful resource, even for the completely uninformed and ignorant. Anyone not wishing to spend a lot of time testing or being geeky would be very well served to just blindly follow the results - and spend that time making photographs instead.

  2. #32
    Abuser of God's Sunlight
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    210 APO-Symmar-L

    "Can you explain this a little more clearly - Are we talking about contact
    printing here, or are we making some very huge assumptions about enlargment size"

    we're by necessity making some major assumptions about enlargement size ... which is something that you have to do unless you're looking at an mtf chart. this is one of the problems with the resolution number game ... it doesn't tell you anything about how the lens
    will perform at different enlargement sizes. the nicest contact prints i've ever seen came from old process lenses like zeiss apo-tessars and kodak copying ektanons. these lenses produced incredible contrast at 5lp/mm or so. but they were very poor performers if measured by maximum visible resolution. enlargements would look soft.

    your experience that the differences between the modern lenses were miniscule (not counting the lemmon) mirror my own experiences. These lenses are very, very good. If you do want to split hairs for whatever reason, or test some older lenses, one of the challenges is testing that mimics the whole range of conditions under which you might use the lens. if you do just one kind of thing (shooting at infinity, at f16, with few movements, for exapmple) then a simple test like the one you did can work really well.

    Otherwise, as a look at almost any group of mtf charts for similar lenses will show you, performance at on axis does not reliably predict performance off axis; performance at 1:10 does not reliably predict performance at infinity; performance at f22 does not reliably predict performance wide open. And performance at 20lp/mm does not reliably predict performance at 5lp/mm. Doing any kind of real-world test, or even air force test target test, that takes these variables into account would take days for each lens and would give you a pile of data that's very hard to interpret or to compare. an mtf chart puts it all on one page in a standardized (almost) format.

    With modern lenses, almost all of this is about splitting hairs, as you suggested. In most real world situations many other factors influencing image quality are likely to be more important. for the amount of money these lenses cost, though, some hair-splitting might be warranted. I chose my lenses over the number 2 choice because it seemed like it would be slightly better at infinity. If I shot in the studio, the choice would have been reversed. I doubt the real difference would actually be visible in most photographs, but who knows? For $900, I wanted some comfort. A resolution test would not have given this information. It would very likely have led me to the opposite conclusion, depending on how it was done.

    Of course, a stumbling block is that mtf charts aren't available for all lenses, especially old ones. This is unfortunate, because older designs are even more likely to exhibit wildly different abilities under different circumstances. My solution was simple: narrow down the field to companies that provide mtf charts. More and more companies do it now, so it's not such a big deal. At any rate, I'm less likely to trust a manufacturer that even today declines to publish this information. For me, being able to narrow the field down, and to do all my comparisons with a few sheets of paper in front of me, actually felt like a lot less geekery and time wasting than trying to go out and do my own tests. And the information is categorically more useful than anything achievable with homegrown tests using resolution charts, or other tests based incorrect assumptions about lens quality.

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