Very high resolution lens?

Discussion in '35mm Cameras and Accessories' started by Aron, Sep 9, 2009.

  1. Aron

    Aron Subscriber

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    I've made two tests using one of my recently acquired cameras (Fujica ST801 with EBC Fujinon 1.8/55) on the resolving power of the lens. For the first test I used a moderate resolution film (Fomapan 200) and the results showed actually the resolution of the film (110 lp/mm) and not lens.

    Today I made new tests using Delta 100 developed in Rodinal 1:25. For the illumination of the test chart I used a 1000W halogen lamp, so contrast was high.

    These are my results (lp/mm)

    Aperture: centre, very close to edge, edge
    f1.8: 85, 57, under 50
    f2.8: 156, 69, under 50
    f4: 161, 89, under 50
    f5.6: 147, 101, 55
    f8: 115, 101, 69
    f11: 69, 55, 69
    f16: 69, 69, 69

    Do you think I was doing something wrong during this test or it is actually possible to achieve such a high resolution with this setup? The lens is a 'Planar' type design.The prints from this camera do look very sharp (to me), even heavily cropped ones taken at f1.8. I'm somewhat surprised. :rolleyes:

    It also is somewhat interesting for me (I used a Tessar lens for a long time), that diffraction already takes its toll at f5.6-f8, most notably at f11.
     
  2. RalphLambrecht

    RalphLambrecht Subscriber

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    Don't know, I never measured resolution that high, but I don't use acutance developers either. I find the value for f/11 peculiar. It does not fit well between the values of f/8 and f/16.

    Why do you think a 1000W lamps creates a high contrast? Higher than what?
     
  3. Denis K

    Denis K Member

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    I haven't done the math and so it's always dangerous to prejudge, but hey, I'll go ahead and do so anyway. I doubt the falloff between f/4 and f5.6 is due to diffraction. I would guess it's more likely to be something like a focus shift on stopping down or some other similar conditions due to lens correction across the aperture range. Between f/11 and f/16 I could believe diffraction could be more significant.

    Denis K
     
  4. Nicholas Lindan

    Nicholas Lindan Advertiser Advertiser

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    The figures look to be about twice what one would expect. How are you counting lp/mm?
     
  5. Aron

    Aron Subscriber

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    For the test I was using the ISO 12233 test chart as it is easier for me to work with it than the USAF 1951 chart.

    On the test chart the width of the lines simply are constantly getting lower and I take the value (1-2-3-4 in my case as the distance between the camera and the chart was fairly high (2.5-2.8m) to minimize the my printer's resolution limit (1200 dpi) and that of the film causing trouble) where I still can count all of the lines (5 black and 4 white), then I multiply this number with 100 and devide it by the height of the test chart on my negative. No need for camera-test chart distance measurments and this way I think it is also more accurate.
    I put the negative in my enlarger (I don't have my microscope with me right now) and used my grain focuser for focusing and measurements.
    The englarger was an acceptably aligned Durst M605 with a Schneider Componon 50mm lens (wide open). The grain was fairly crisp, so I believe there were no big issues regarding the sharpness of the lens.

    The whole projected negative was exactly 32cm high using the heighest column height (13.3x magnification) and in this position was the negative measured. Assuming the negative was 24mm high, the height for the chart was calculated to be 2.18mm.
    I checked it a few times just to be sure I wasn't too optimistic and my eyes didn't try to see lines where it would be only one blurry thick line and I arrived at practically the same numbers both of the times.

    Could it be the common confusion of lines/mm and line pairs/mm?

    I think strong lights create higher contrast than just one candle, for example. If we think about 100% black (hypothetical) and a silvery surface, the black will never radiate back any light, no matter how strong it is, on the other hand the silvery surface will reflect more and more as we use consequently increase light. Hence the contrast will get higher. And if I understand it well, resolution also depends on contrast. Maybe I'm wrong at this point, but still, it was much easier to focus on the test target this way, so it had at least one benefit.
    Some one also mentioned in an early post, that under practical circumstances one should hope for approximately half of the resolution values measured in a lab. If this is true, many factors can contribute to this, improper focusing or camera shake, but I think also contrast, since the contrast between two points close to each other in a real scene is often lower than the contrast present on a test chart.

    Aron
     
  6. Aron

    Aron Subscriber

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    One more thing, just if some one might be interested: the same test with an uncoated filter attached to the lens resulted in a loss of resolution of 20-25% magnitude. Some filters could be that bad.
     
  7. Denis K

    Denis K Member

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    At f5.6 on a 35mm lens the size of the Airy disc should be about 7.5 microns which if I'm correct would lead to 133 line/mm or 66 lp/mm. This means the 147 figure Aron listed seems high to me any way you figure it.

    Denis K

    Correction: To be more accurate, the "diameter" of the Airy disc would be 7.5 microns, which would make the radius half of that or 3.75 microns. Furthermore, lens resolution calculations typically assumes that you can resolve two points separated by the Airy radius and not the diameter as I calculated above. This would lead to a resolution of closer to 266 lp/mm at f/5.6 in light at 550 nm.
     
    Last edited by a moderator: Sep 10, 2009
  8. keithwms

    keithwms Member

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    Just a stray comment, since I don't know the specifics of this test you did: in my experience the Fuji EBC lenses are veeery contrasty. I don't mean that as a criticism- for landscape and such they never disappointed me.
     
  9. Aron

    Aron Subscriber

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    Denis,
    thank you for your helpful comment. It is not very easy to clearly see where the resolution limit is for a given aperture (without a device contstructed for the task, I can't get rid of the human factor at evaluation) on this chart, especially that despite the kind of film I used, grain still proved to be a major problem. I tried to be pessimistic and I got a number of 130. This is below the theoretical top resolving power at the mentioned f5.6.
    However, for the other apertures I examined again (1.8-2.8-4) the earlier results seemed to be correct.

    May I conclude that the simple mistake was made of taking the results as lp/mm and not as lines/mm? If yes, are these results still very good?

    Aron
     
  10. Henning Serger

    Henning Serger Member

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    Hello Aron,

    I have nearly 20 years experience in such tests, so may be I can help you.

    That is not automatically the case. It depends on the surface and the reflection characteristics of the surface of the test chart.
    If it is matte and little reflecting, or brillant and strong reflecting. In most cases not the power of the light, but the direction of the light has influence. In this case, when your halogen lamp is working in a specific angle, it may happen that even the black lines are a reflecting and turning to grey, the object contrast is significantly reduced.
    A proper, even and indirect lighting with no reflection spots of the test chart is necessary for a reliable test.

    In general it is possible, yes. With an excellent lens, modern films, exact focusing and avoiding of camera shake extremely high resolution values are possible.

    You may have a look at the scientific tests made at Carl Zeiss in Germany.
    They are published in the Zeiss camera lens news 17, 19, 20, 24 and 30 (look on their home page www.zeiss.de).
    For example they achieved 180 linepairs per millimeter with Kodak TMX, 170 linepairs per millimeter with Fuji Velvia, and 160 lp/mm with Acros 100. With Agfa Ortho 25 250 lp/mm. At an object contrast of 1:100.
    In an MTF test Dr. Hubert Nasse, chief optic designer of Zeiss, got 180 lp/mm with TMX.

    Or look here, Delta 100 test:

    http://www.imx.nl/photo/technique/page153/page153.html

    My own test results:
    I am working with a test chart with quite low contrast, only 1:16, four stops.
    Because in nearly all scenes you have at least such a contrast, often higher.
    I want to know how good my lenses and films are in low / moderate contrast situations.

    With a Zeiss ZF 2/50 at aperture 4 and 5,6 in the centre of the negative I achieved 130 - 150 linepairs per millimeter with Ilford Delta 100.
    130 lp/mm are clearly seperated, with 150 lp/mm you can still see a contrast difference. Delta 100 is one of my favourite films since its introduction 1992.
    For these tests a developer test was integrated (Spur HRX-3, Spur SD2525, Rollei RLS / CG512, Rodinal 1:50; highest resolution values were achieved with HRX-3 and RLS).

    With Kodak TMX and Rollei Retro 80S I got nearly the same resolution, the differences between these three films concerning resolution are so small that they are not really worth to be mentioned. Resolution of Acros 100 is a bit lower, but you can see the difference only under a microscope.
    The difference in grain is a bit bigger: Retro 80S has the finest grain, then Acros 100, TMX and Delta are following.

    With Rollei Ortho 25 / Adox Ortho 25 (a film made by Filmotec) I got resolution values of about 150 - 170 linepairs per millimeter, with Rollei ATP and Spur DSX ( = Agfa Copex Rapid) 170 - 200 lp/mm.
    And with Spur Orthopan UR / Adox CMS 20 (older version of Agfa Copex HDP microfilm) I reached the limits of my microscope: 270 Lp/mm. Probably the resolution is even a bit higher, but my microscope delivers not enough magnification to further analyse it :wink:.
    These high resolution films are incredible.

    Best regards,
    Henning
     
  11. Henning Serger

    Henning Serger Member

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    Aron,

    it is difficult to write formulas here with this text format, therefore I have done the calculation for you and will try to explain it as simple as possible:

    1. Measure the lines on your test chart: Most likely there will be one black line and one white line per millimeter, and the number 1.
    And at the next pattern two black lines and two white lines on one millimeter and the number two. And so on.
    So the numbers give the linepairs per millimeter on the original test chart.
    Check whether this is the case with your test chart.

    2. Your distance test chart - film plane was 2,50 meters.

    3. Focal length of your lens 50mm.

    4. Resolution: If you can seperate the lines of number 2 on the negative, than the resolution is 96 linepairs per millimeter.

    If you can seperate the lines of number 3 on the negative, than the resolution is 144 linepairs per millimeter.
    Number 3,5: 168 lp/mm.

    Best regards,
    Henning
     
  12. lxdude

    lxdude Member

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    I'd just like to add to comments on the lens.
    My first good camera and lens in 1974 were the ST801 with the 55/1.8. It's all I used for about 3 years, including with extension tubes and/or reversed. To this day that lens' results hold up to anything I've used from the other makers. The other EBC lenses I've had (no zooms) have all been sweet performers. Color, contrast, sharpness, all great. Focus and aperture still smooth and reliable. Something I've noticed is, after all this time, they all have very little dust inside.
    So whether your numbers are accurate or not, expect great results from that lens.
     
  13. RalphLambrecht

    RalphLambrecht Subscriber

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    I'm not questioning your experience, but why is it, you think, that I have never measured a resolution that high. Not with a Mamiya lens, a Hasselblad lens or any other lens. I get 65 lp/mm with Hasselblad and up to 90 p/mm with Mamiya lenses. My test targets have a higher contrast than yours, and still, nowhere close to your numbers. I don't use high-acutance developers (D76 1+1) but the same films you mentioned. Are we counting differently?
     
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  15. RalphLambrecht

    RalphLambrecht Subscriber

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    Henning

    With this you mean that each line is 0.5 mm wide, correct?
     
  16. ic-racer

    ic-racer Member

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    I just read this thread and coincidentally I had just printed a negative from my archive for a friend. The negative was from 1974 and my camera at the time was a ST701 with the EBC 55/1.8. I remember commenting to myself when printing the negative that it was very sharp. Seem like I have come full circle because the ST701 is long gone but my favorite Large Format lenses are Fujinons.
     
  17. Henning Serger

    Henning Serger Member

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    Hello Ralph,

    probably the difference is because of the following reasons.

    1. In general medium format lenses have a bit lower resolution values than lenses for 35mm (yes, there are some exceptions from this rule). The bigger the lens diameter, the more difficult it is for the optic designer to design a lens.

    You may have a look at these medium format lens tests:

    http://www.hevanet.com/cperez/MF_testing.html

    These tests were made with TMX. Just have a look whether you find the lenses you have tested.
    But there you find some Zeiss and Mamiya lenses with resolution values of 100 lp/mm - 120 lp/mm in combination with TMX (system resolution).

    LF lenses: http://www.hevanet.com/cperez/testing.html

    2. If we photograph a test chart in a distance of 2 or 3 meters, absolutely exact focussing is necessary to achieve more than 100 lp/mm resolution. The focus must be exactly down on the millimeter.

    The problem with focusing is, that we don't have really exact focusing systems. Neither our manuel focusing systems (split image, matte screen, microprism) nor the AF systems deliver the precision we need to exploit the capabilities of our lenses and films.

    Therefore we have to do a simple, but effective trick: "Focus bracketing". Shooting several frames, each frame newly focused with a sligtly different focus. We make a series and choose the pictures were the focus is dead on.

    When I do my lens and film tests, e.g. with TMX, then always some negatives have resolution values of only 80 or 90 lp/mm. Because the focus is a bit in front of or behind the flat test chart.
    But some shots of the test series are absolutely precise in focus, because of the "focus bracketing".

    And with focus bracketing you can also avoid another problem with lens resolution tests: Focus shift when stopping down. A lot of lenses have this characteristic (have a look at Dr. Nasses report about the lens MTF tests I have mentioned in my first post).

    3. To exploit the full resolving power of our lenses and films we have to avoid camera shake completely. That means very stable tripod ( I am using a Berlebach Report 3032) and MLU and short shutter speeds (1/250 or even shorter).
    Vibrations make a big difference in resolution. I have compared my F90X with my F6. Even at 1/250 on the Berlebach tripod I get much higher resolution with the F6, because mirror and shutter are much better damped and have less vibration (even with the MLU not activated). And with MLU the difference is much more significant of course.

    My English ist not the best, I hope my explanations were helpful for you. Your German is much better than my English :wink:, so if you are interested in further information, let us continue per pm. And Leverkusen is not so far from me, if you want to see my test pictures, than it is no problem at all to show you.

    Best regards,
    Henning
     
  18. Henning Serger

    Henning Serger Member

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    Yes, correct. One millimeter with one 0,5mm black line and one 0,5mm white line
    = one linepair.

    Best regards,
    Henning
     
  19. Aron

    Aron Subscriber

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    Henning,
    I will not be able to continue testing for a week, but i'll continue after using your advices.
    I'm just getting even more interested on the topic with the help of the already many helpful posts. Can you recomend me some articles where I can find more info on the topic of lens resolution and how different lens designs can affect it?

    Aron
     
  20. Henning Serger

    Henning Serger Member

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    Hello Aron,

    at first step you probably find some interesting information in the Zeiss camera lens news number 17, 19, 20, 24 (resolution), and 30, 31 (reports of Dr. Nasse concerning lens design and MTF). I think that is enough to read for the beginning :wink:.

    Best regards,
    Henning
     
  21. Aron

    Aron Subscriber

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    Henning, my mistake, you already recommended these articles in your first post. Maybe also my eyes are needed to be checked. :wink:

    Aron
     
    Last edited by a moderator: Sep 10, 2009
  22. RalphLambrecht

    RalphLambrecht Subscriber

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    Henning

    I'll go PM from here!
     
  23. Ed Sukach

    Ed Sukach Member

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    ??? Are we talking about LENS resolution, or FILM resolution?

    In LENS testing (at least in the old, Luddite, Optical Bench way), no film or ground glass is used: the microscope is focused on the aerial image - much the same as "Grain Focusing" in the enlarger.
    Introducing film into the testing provides the opportunity for a number of elements that will invariably degrade the results: flm flatness, emulsion/ developing charactersitics, mechanical "shake" of the support system ...

    Is it possible to see exteremly high resolution in any area of any given lens? Absolutely, but maximum resolution, by itself, is an incomplete test of the performance of a lens.
     
  24. Q.G.

    Q.G. Inactive

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    As you say, testing lens resolution by itself is an incomplete test. So we are talking both lens and film resolution.
    Real life lens use involves both a lens and film anyway.
    :wink:
     
  25. Henning Serger

    Henning Serger Member

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    Hello Aron,

    I have just seen a little mistake: Your Fuji lens has 55mm, not 50mm.

    Here are the corrected calculations:

    - Number 2: 87 lp/mm
    - Number 3: 130 lp/mm
    - Number 3,5: 152 lp/mm

    Best regards,
    Henning
     
  26. Henning Serger

    Henning Serger Member

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    Ralph,

    I have send you a pm.

    Best regards,
    Henning