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Thread: Diffraction. When does it really matter with LF?

  1. #21
    Drew Wiley
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    Re: Diffraction. When does it really matter with LF?

    Good assessment, Adam. But to the above options, you could also add that diffraction is just another potential tool, to either employ or set aside according to the specific goal in mind, with critical sharpness being the opposite tool. Some like to use a broad paintbrush, others a fine narrow one. Or the whole depth of field problem might force your hand : ULF shooters generally contact print, yet often need very small apertures anyway due to serious depth of field issues.

  2. #22

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    Re: Diffraction. When does it really matter with LF?

    Goes back to what the image-maker's print goals are..

    IMO group f64 held a significant influence on many LF image creators. This was the ideology-belief everything in the print image to be ~sharp~. There was no question this greatly influence my own print LF image making goals. That was circa early 1980's. That was a time when few images were made with apertures larger than f16, most were f22 to f45 as needed. Going up in film format size made the taking apertures smaller, typically f32 to f45 and at time may be a tad smaller.. This was driven by a list of factors from camera alignment precision, film flatness, the ideology of everything in the image in focus being the primary goal.

    ~Except, LF was not the only fit format being used for image making.

    There was 35mm, 120, video image making cameras used. Add to this films made by folks like Stanley Kubrick, Alfred Hitchcock, Steven Spielberg, Ken Burns and many others.. they nice illustrated the visual effectiveness and emotional expressive power of selective focus and the value of lens out of focus rendition.

    Add to this, the entire world of Soft Focus or "sort-of-focus" lenses that are most effective on sheet film formats 5x7 and larger.

    Since those early days of LF image making, the method today is to stop the everything in the image required to be in apparent focus.
    It has since evolved to what is the expressive value of holding specific items in the image in focus, what would result in a more expressive and effective image if specific areas in the print are rolled out of focus. Knowing this along with the very real effects of diffraction and the power of view camera movements to control what is in focus -vs- what cannot be held within the plane of focus (yes it curves as camera movement is applied) delivers LOTs of options as to using what is in or out of focus as a tool for expressive image making.

    Over time, the lens choices reflect this methodology..

    APO process lenses or Dagor lenses are preferred for everything in apparent focus images. This means a taking aperture of f16 to f45. For images that are selective focus or controlled rolling out of focus lens choice becomes Tessar.

    Camera movements and what they can do greatly influences taking aperture. The drill is to figure out what the print image needs and should be.
    In the case of everything in the image to be in apparent focus, camera movement is applied as needed to achieve this with the largest possible taking aperture. There is no reason to close down the aperture more than absolutely needed. This demands fit to be flat in the film holder, camera to hold and be precise between front to rear standards with camera movements being precise, accurate and stable. This is how to avoid diffraction and extracting what is possible with a view camera to meet a print image goal.

    Example (previously posted). Image of this building was made with a 8-1/2" f6.3 Kodak Commercial Ektar. Taking aperture is f11, 5x7 film format, Sinar C camera. Camera movements were applied as needed with the lens at f6.3, then stopped down just enough to bring the image areas that must be in focus, into apparent focus. Flat do not believe in closing down the aperture down more than needed.
    Click image for larger version. 

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    Keep in mind lens focuses on a plane, as the aperture is closed down, image rendered becomes apparent focus unless the image being recorded is with the lens set to true infinity. In this case, large lens apertures can be applied effectively for a given lens design and camera's ability to hold alignment, precision, and film absolutely flat.

    Then there is the obsession with "sharpness". There are many aspects to what sheet film can offer that is far beyond "sharpness".

    BTW, if contact prints are made, stopping down past f64 is often not an issue or problem. Or why 8x10 or larger film sizes can make really GOOD contact prints.



    Bernice

  3. #23
    Vaughn's Avatar
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    Re: Diffraction. When does it really matter with LF?

    Quote Originally Posted by Dan Fromm View Post
    Re Greg's post #17 above, +1. Sharpness is overrated.
    Agreed. Just another tool -- use wisely.
    "Landscapes exist in the material world yet soar in the realms of the spirit..." Tsung Ping, 5th Century China

  4. #24

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    Re: Diffraction. When does it really matter with LF?

    If you really want to get this out of your system, I have applied modern tech to help evaluate what your lenses are doing...

    I now use my large 4X5 studio camera as a optical bench by using a DSLR mounted on a pine plank that fits in the Graflok back holder with a plumbing extension for holding a Nikon F (or other) lens mount so the camera can ride the back... (Or buy an adapter for not too much...) Then you can analyze different areas of the focal plane (by using camera shifts) and directly observe different areas in real time...

    For instance, you can check your lens at all the aperture settings, where you can notice it might be mushy at its extremes, like wide open, but when you stop down a stop or two, the image "firms" up, or at the other end of the scale, f22 might be good but image mushes out below that somewhere... And there are other tests like color saturation, overall contrast, edge sharpness, color fringing etc... But this tends to test the lens, but not overall response of the entire film/printing system... But you start getting an idea of the tonality range...

    You can sort lenses into different "types" of contrast/resolution that can combine into different film effects, like soft or harder contrast, overall softer or harder sharpness, lower or higher general key etc and start doing film tests of the lenses of how they render on film... Generally, you will be looking at the scale across film range to look for the "look" the paticular lens will render in the scene and with materials etc... And armed with testing, you make better choices to decide the "look" you want...

    Steve K

  5. #25
    Mark Sawyer's Avatar
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    Re: Diffraction. When does it really matter with LF?

    Why isn't diffraction considered an optical aberration? It's missing from the conventional list of aberrations.

    Late night pondering...
    "I love my Verito lens, but I always have to sharpen everything in Photoshop..."

  6. #26
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    Re: Diffraction. When does it really matter with LF?

    It's missing from the conventional list of aberrations? That itself might be an aberration.
    "Landscapes exist in the material world yet soar in the realms of the spirit..." Tsung Ping, 5th Century China

  7. #27

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    Re: Diffraction. When does it really matter with LF?

    Quote Originally Posted by Mark Sawyer View Post
    Why isn't diffraction considered an optical aberration? It's missing from the conventional list of aberrations.

    Late night pondering...
    Well, it can't be corrected.

  8. #28

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    Re: Diffraction. When does it really matter with LF?

    Caution on this, Digital image sensors have a substantial stack of filter in front of the silicon sensor array. This is done to limit IR, separate color and more.. Film does not have this stack of filters which can add a variable to image produced on film -vs- digital image sensor.


    Bernice


    Quote Originally Posted by LabRat View Post
    If you really want to get this out of your system, I have applied modern tech to help evaluate what your lenses are doing...

    I now use my large 4X5 studio camera as a optical bench by using a DSLR mounted on a pine plank that fits in the Graflok back holder with a plumbing extension for holding a Nikon F (or other) lens mount so the camera can ride the back... (Or buy an adapter for not too much...) Then you can analyze different areas of the focal plane (by using camera shifts) and directly observe different areas in real time...

    For instance, you can check your lens at all the aperture settings, where you can notice it might be mushy at its extremes, like wide open, but when you stop down a stop or two, the image "firms" up, or at the other end of the scale, f22 might be good but image mushes out below that somewhere... And there are other tests like color saturation, overall contrast, edge sharpness, color fringing etc... But this tends to test the lens, but not overall response of the entire film/printing system... But you start getting an idea of the tonality range...

    You can sort lenses into different "types" of contrast/resolution that can combine into different film effects, like soft or harder contrast, overall softer or harder sharpness, lower or higher general key etc and start doing film tests of the lenses of how they render on film... Generally, you will be looking at the scale across film range to look for the "look" the paticular lens will render in the scene and with materials etc... And armed with testing, you make better choices to decide the "look" you want...

    Steve K

  9. #29
    Drew Wiley
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    Re: Diffraction. When does it really matter with LF?

    Mark - Diffraction affects different wavelengths differently. I discovered this long ago in reference to the setting sun over sharp ridges where there is extremely clean air, first at Comb Ridge in Utah, then in Kauai. At first I blamed my highly-corrected new lens for the color fringing, but then saw it with my own eyes. The rays were truly bent differently over sharp geological edges in the distance. Something analogous happens with very small apertures, especially in high-magnification optical microscopy. There are very expensive sophisticated methods for correcting this. The primary wavelengths are completely separated, then more precisely re-aligned through electronically controlled magnetic mirrors - add about another $40,000, plus digital output afterwards. There might be similar technology in the latest astronomical equipment - add 400 million dollars, I'd imagine.

  10. #30

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    Re: Diffraction. When does it really matter with LF?

    Quote Originally Posted by Greg View Post
    In the late 1970s and early 1980s I shot a lot of waterfalls in New England with my 8x10 and a 12" Wollensak Velostigmat Series II. All exposures shot at f/64 or f/90. At the time I made contact prints on Varigram or Varilour FB paper. Around 10 years ago scanned the negatives and made digital negatives to print Platinum/Palladium prints from. Loss of sharpness from diffraction is definitely in the original 8x10 negatives if you look at them under a low power X4 Loupe. Holding the prints side by side at arm's length, most people would say, resolution wise, that the FB prints are a tad bit sharper than the Platinum/Palladium prints. Aesthetically and tonality wise, the Platinum/Palladium prints far outshine the FB prints. Several of my friends/relatives are not photographers and when asked which print is sharper, all responded that the Platinum/Palladium print was definitely sharper. When I am doing Photomicrography or Photomacrography diffraction, to me, is a major concern and factor. When I am shooting outside with my 8x10 or 11x14, diffraction matters little to me. The image matters all to me. If I were concerned with loss of sharpness from diffraction, I just might never take out my 8x10 and 11x14 ultraWA pinhole cameras. To me the final image in the final print is what matters the most...
    Comments most welcome
    This is a good example of how contrast affects apparent sharpness in ways that matter more than actual resolution.

    Reminds of me of this essay on sharpness and pinholes and deciding what size is best for your use case:
    The Pinhole Camera Revisited

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