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Thread: Is there any real utility to ULF?

  1. #91
    All metric sizes to 24x30 Ole Tjugen's Avatar
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    Re: Is there any real utility to ULF?

    Quote Originally Posted by Patrik Roseen View Post
    PS: Now I need to get my knowledge corrected regarding DOF, Diffraction, CoC etc...elsewhere.
    I haven't visited the lab, but I have seen Teddan's print. Up (very) close.

    May I suggest "Optics in Photography" by Rudolf Kingslake for anyone who wishes to get the confusion out of "Circle of Confusion"? It requires a little work to get through, but no more than Leslie Stroebel's book does. In both cases working at it until you really understand what it's all about is really the only way to learn anything.

  2. #92

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    Re: Is there any real utility to ULF?

    thank you QT

  3. #93
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    Re: Is there any real utility to ULF?

    Quote Originally Posted by Jorge Gasteazoro View Post
    You are correct in the focal lenght determination. It has nothing to do with the shutter, but the bigger the lens cells to correct for aberrations the bigger the shutter and the bigger the entrance pupil. I am sure you have seen two lenses of the same focal lenght but one is much smaller than the other. While the ratio of the f stop is the same, the diameter of the entrance pupil is much bigger for the bigger lens, thus avoiding difraction. Of course this does not mean you do not have difraction with the bigger lenses, but it is mostly at the edges, and since they have such great coverage it is negligible.
    Not sure what your mean about the ratio of the f stop being the same but the entrance pupil is bigger? The f-stop is the size of the entrance pupil so diffraction is intrinsically linked to f-stop for the same focal lenfth (i.e. f64 will always have the same size diffraction when focused at infinity, regardless of focal length)

    Shame about the scanner

    Tim

  4. #94

    Re: Is there any real utility to ULF?

    f64 will always have the same size diffraction when focused at infinity, regardless of focal length
    I know difraction as the interference of the light wavelenght by the pupil. IOW the hole is so small that the light wavelenght degrades by interference. So for example of the lenses I have owned I have a 300 sironar N in a copal 3 and I had a 300 mm in a copal one. At f/64 the entrance pupil of the Sironar was about 5 mm, on the one with the copal 1 it was about 1 mm.

    While I have used the one in the copal 3 at f/90 without any loss if resolution due to difraction, I could not use the one in the copal 1 at f/90 because I was able to clearly see loss of resolution in the negatives. I don't know what MTF tables say, but real life practice tells me this is happening..

  5. #95
    All metric sizes to 24x30 Ole Tjugen's Avatar
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    Re: Is there any real utility to ULF?

    No Jorge, a 300mm lens at f:64 has an entrance pupil at slightly less than 5mm. That's the definition of f-stop.

    While diffraction is a result of the edges of the aperture, it gets enlarged along with everything else with longer focal lengths. So in the end it all cancels out, and you end up with diffraction being only dependent on f-stop.

    MTF tables don't enter into this at all, you get exactly the same diffraction with a (large) pinhole.

  6. #96

    Re: Is there any real utility to ULF?

    No Jorge, a 300mm lens at f:64 has an entrance pupil at slightly less than 5mm. That's the definition of f-stop.
    hmmmm... you are right, it should be the same diameter in the entrance pupil, yet it is not what I saw in the lenses I had. I wish I still had the other so you could see the difference. Maybe it was mislabeled.

  7. #97

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    Re: Is there any real utility to ULF?

    Quote Originally Posted by Jorge Gasteazoro View Post
    hmmmm... you are right, it should be the same diameter in the entrance pupil, yet it is not what I saw in the lenses I had. I wish I still had the other so you could see the difference. Maybe it was mislabeled.

    View Camera Technique by Stroebel treats this topic.

    See page 99 ( if you have the 5th edition). Stroebel provides a diffraction-limited formula for resolution. It is R=1800/f-N, where R is the resolution in lines/millimeter, 1800 is a Constant, and f-N is the f-number. The formula is approximate because diffraction is different for Red, Green and Blue light, and the Constant of 1800 is an average figure.

    Diffraction-limited resolution is an absolute, and is the highest possible resolution that can be had at a given aperture. The formula works for all lenses regardless of focal length. The diffraction-limited resolution at a given f-stop is the same for a lens of 200mm as for one of 800mm. It has nothing to do with depth of field, depth of focus or circle of confusion. Ole is correct in that it is dependent on f/stop. It is also dependent on how the Constant for wavelength is calculated.

    Sandy King

  8. #98

    Re: Is there any real utility to ULF?

    Quote Originally Posted by sanking View Post
    View Camera Technique by Stroebel treats this topic.

    See page 99 ( if you have the 5th edition). Stroebel provides a diffraction-limited formula for resolution. It is R=1800/f-N, where R is the resolution in lines/millimeter, 1800 is a Constant, and f-N is the f-number. The formula is approximate because diffraction is different for Red, Green and Blue light, and the Constant of 1800 is an average figure.

    Diffraction-limited resolution is an absolute, and is the highest possible resolution that can be had at a given aperture. The formula works for all lenses regardless of focal length. The diffraction-limited resolution at a given f-stop is the same for a lens of 200mm as for one of 800mm. It has nothing to do with depth of field, depth of focus or circle of confusion. Ole is correct in that it is dependent on f/stop. It is also dependent on how the Constant for wavelength is calculated.

    Sandy King
    I know Ole is right, I am just wondering why the hole looked so much smaller in one of the lenses.

  9. #99

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    Re: Is there any real utility to ULF?

    Sandy, I've been following this thread intermittently and perts have been interesting. Stroebel gives a form of the classic Airy disc calculation in the form of cycles per mm. Thus for an f/5.6 lens we get about 320 cycles per mm. resolving power. This must assume a perfect optical lens since 320 would not be achievable with a full visible light lens. Maybe the best would be about 1/5 of that resolving power. Although using monochromatic light both Zeiss and Nikon have been able to produce lenses in the 600 to 800 cycles per mm. range for microchip replication purposes. The Ultra Micro Nikkor series being one example - albeit covering only about a 15 by 15 mm. reduction field.

    A convenient nomograph for resolving power determination for a perfect lens can be found on page 976 of the SPIE Handbook of Photographic Science and Engineering (my bible). It's interesting because we see how difficult it is to design the glass to reach the limit imposed by diffraction effects esp. at wide apertures.

    Nate Potter

  10. #100

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    Re: Is there any real utility to ULF?

    > From Jorge, So for example of the lenses I have owned I have a 300 sironar N in a copal 3 and I had a 300 mm in a copal one. At f/64 the entrance pupil of the Sironar was about 5 mm, on the one with the copal 1 it was about 1 mm.

    > From Ole... No Jorge, a 300mm lens at f:64 has an entrance pupil at slightly less than 5mm. That's the definition of f-stop.


    Thank you Ole for taking the baton..... sheeeesh.... The entire premise behind the fstop system, is that f ratio is ALWAYS THE SAME, REGARDLESS OF LENS FL ! If it weren't, our light meters would all be useless ! If the same fl lens has a larger diam apt. opening vs. another lens of the same fl, one of them has the wrong shutter on the lens!




    > Diffraction-limited resolution is an absolute, and is the highest possible resolution that can be had at a given aperture.


    Sandy, key words being "highest possible"..... one of the previous posters kept missing this point.... the wider the lens coverage, the further from "highest possible" the resolution becomes, hence why there is "diminishing levels of return" in photography, i.e. bigger formats are not always better. If they were, I would shoot mostly 20x24 :-)




    > This must assume a perfect optical lens since 320 would not be achievable with a full visible light lens. Maybe the best would be about 1/5 of that resolving power. Although using monochromatic light both Zeiss and Nikon have been able to produce lenses in the 600 to 800 cycles per mm


    Nathan, nice post. From test results I have seen, and the lenses I have tested myself here is some findings..... high quality 35mm can have aerial resolutions at diffraction limited values.... the BEST MF lenses are very very close to diffraction limited, specifically Mamiya 7 lenses, (Mamiya achieved 350 lp/mm aerial resolution at f4)..... the best of the modern bunch of 4x5 lenses fall just a tad below the M7 lenses (specifically the 110, 150 SSXL), but there is others, most fall in the normal fl range....most of the older 4x5 or larger image circle lenses fall off up to about 30 - 40% of diffraction limited values... and older vintage LF lenses can fall down to 70% of diffraction limited values. Chris Perez's list of LF lens tests represent a bounty of data in this regard. Kudos to Chris for his contributions. Since MTF data is not available for many vintage lenses, Chris test results often are the best reference.


    It's interesting to note, lens designs really started to make huge advancements with the advent of optical software. By the mid 90's, the big makers were benefiting greatly from the ability to design lenses with huge optical gains vs. the previous generation. For example, comparing some of the digitar lenses to LF lenses of the same fl and "almost" the same coverage.... the digitars lenses have very similar MTF curves throughout the radius, however, the curve lines for the LF lenses are at 5,10,20, whereas the Digitar lenses are recorded at 20,40,60. This represents a 300% gain in aerial resolution..... whereas previous to this "optical software era", it was impressive when lens makers jumped aerial resolution 10 - 20%.


    With the advent of digital, its easy to test these lenses... I had a custom back made to accept a digital SLR. Shooting Test Targets is a fast and easy way to compare lenses aerial resolution. Using a small, highly dense sensor makes this process a breeze vs. testing with film. During these tests, I also learned how long shutter times (several seconds) can also degrade resolution, as the mechanical shutters, specially the 3's vibrate the lens!


    I find it ironic, that throughout the early days of photography, the means to higher resolving prints was by using larger formats, and their corresponding larger fl lenses w/ longer shutter speeds. This was a result of 1) the lenses of all fl's were all poor resolvers (compared to today), and 2) the recording media was the same for all formats. (same as film today). However, with the advent of super high resolving digital lenses, combined with super dense digital sensors (allowing a smaller format size, therefore shorter fl lenses)...... the trend of "bigger for more resolution" is now being reversed.



    With these highly dense recording media (digital sensors vs. film) the photographic process can finally benefit by using shorter fl lenses which benefit from MUCH higher aerial resolutions as a result of avoiding the dreaded apt. diffraction effects. This is why the 39MP backs today have been considered on par with scanned 4x5 film. (regardless which is actually better is not relevant, the fact they are this close demonstrates the value of shorter fl lenses combined with smaller formats)


    Some of the optical engineers I work with are designing 100MP sensors which will be close to 6x7 format. This will make another monumental jump in recording higher resolutions images with shorter fl lenses and faster shutter speeds. It took the advent of highly dense digital sensors to defeat (or drastically reduce) the physical limits of apt. diffraction, which has always been the achillies heel of gaining more resolution in photography. Digital sensors finally reversed the "bigger is better" systematic approach to gaining resolution. Who would have dreamed this just 10 years ago? A revolution right during our life time.... I find it quite fascinating, even if I never use them.


    Disclaimer - other than family snapshots, I ONLY SHOOT FILM! :-)

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