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Thread: Sharp 75mm (no diffraction) ???

  1. #1

    Join Date
    Jul 2008
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    46

    Sharp 75mm (no diffraction) ???

    Hi,

    I have a Nikkor 75mm f/4.5 SW and have now used it for digital and run into problems of diffraction also at around f/11. My Rodenstock 150 Sironar-N f/5.6 is sharper at f/5.6-16. Thus... I need trade it for another 75mm...

    What would you recommend, and why? Please give me advise on OLD/NEW;

    A) Schneider Super Angulon f/5.6 MC or not MC

    B) Rodenstock Grandagon /N f/4.5

    C) Other choices


    and, in regards to

    1) sharpness/diffraction

    2) Focus shift (depth of field is shallow and focus need be very exact with digital)


    Much Kind Thanks!!!

    Anders

  2. #2

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    Re: Sharp 75mm (no diffraction) ???

    Hi HK

    I have my suspicians. If this lens isn't designed for digital (field flatening for example) then the losses will be quite substandial while not remarkable for a 150mm.

    Sensors require light rays to be perpendicular to their face. Angular rays that are off by a few degrees are not recorded or at best partially recorded. That is why all early digital cameras (except Olympus) lost 30% to 40% of their image resolution. Over time, first Olympus, then Sony, then Tamron, and finally the rest realized that field flatening elements were required for effective use of digital optics.

    If you add to this that "superwide" lenses were optimized for 1:1 and could not be used effectively for focus distances farther than the hyperfocal distance then horrendous field curvature problems occur.

    Lynn

  3. #3

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    Re: Sharp 75mm (no diffraction) ???

    As Lynn noted, lenses not designed for digital can sometimes produce problems when used with a digital back. That is why manufacturers such as Schneider and Rodenstock makes `digital lenses', in addition to their regular line of large format lenses, which are optimized for use with the sensor arrays in such backs. But these lenses typically don't cover the full 4 x 5 frame. In addition, when used with the larger digital backs, e.g. 72 x 96 mm, they may not allow much movement. The Schneider Digitars seem to do better in this regard than the Rodenstock digital lenses.

    I'm not sure what you mean by diffraction. The problem with digital backs and standard lenses is that the sensors don't work very well for light coming at a large angle. Diffraction doesn't have much to do with that.

  4. #4

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    Re: Sharp 75mm (no diffraction) ???

    Please don't take this the wrong way, it's meant to be helpful, not offensive. But based on a couple other things you say here I'm wondering whether you understand what diffraction is, what causes it, and how it shows up in a print. It would be useful if you provided more information (e.g. what digital camera are you using and what size prints you're making) and if you could post a photograph or two. It's unusual for the effects of diffraction to be objectionable at f11, especially if your camera doesn't have a full-frame sensor.

    In general, the 75mm Nikkor SW is an excellent lens and is the equal of the others you mention. I'd be a little surprised if any of them were any better in terms of diffraction than the one you have but then I'm not a lens expert either.

    All other things affecting depth of field being equal, I'm not aware that depth of field is inherently shallower with a digital camera than with a film camera.

    All other things being equal, a multi-coated lens is better than a single coated or non-coated lens in terms of flare (which isn't the same thing as diffraction).
    Brian Ellis
    Before you criticize someone, walk a mile in their shoes. That way when you do criticize them you'll be
    a mile away and you'll have their shoes.

  5. #5

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    Jul 2008
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    Re: Sharp 75mm (no diffraction) ???

    Hi,

    Thanks for above replies and let me clarify;

    I use it with a Leaf Aptus 65 digital back (28.6MP on a 44x33mm sensor).

    My use is for panoramix stitching in one row, up to 118m width. Thus no digitar lenses will work because they have too small image circle. Indeed both my 58mm Schneider 5.6 XL and Rodenstock 150mm Sironar-N 5.6 result in SHARP images. Optimum aperture is at f/11. At f/16 I notice some diffraction begin and wider aperture result in very shallow focus of course.

    While the 75mm 4.5 SW Nikkor is indeed suffice sharp for film, diffraction (softness) is obvious when using my digital back because the digital back has higher resolution than the Nikkor lens is capable to resolve (this is a documented problem with e.g. high resolution cameras such as Canon 5DII). My 58mm and 150mm can resolve the resolution of my digital back very well f/5.6-11, but f/11 seem optimum.

    Indeed lens fabricators want us to buy digitar lenses with tiny image circles. In my opinion we are over sold by their marketing! I do not want such lens because they do not work for panoramic size I use, and are also $$$. I have found suffice sharpness in SHARP traditional lenses such as my 58mm and 150mm. However, if one search for top Leica like sharpness one needs digitar lens. My 58mm and 150mm are at least as sharp as my Mamiya 645 lenses, except the Mamiya 28mm digital designed lens which is sharper.

    It is correct that light rays should preferably be parallel for sensors. However my 58mm is wider than my 75mm Nikkor and I am actually keen on eventually going wider with a 47mm! It depends on what one shoots and what can be accepted in the outer regions of a panorama. I shoot landscapes and do not aim at absolute pixel peeping in widest regions of a panoramic image. For a 75mm lens there seem to be little to no problem but I need a higher resolving lens to complete be sure. With the 58mm there is light fall off in outer regions of a full width panoramic frame. Perhaps that aids to hide any problems due angle of light, not sure yet. Of course, within the center region of a panoramic stitch there will not be a problem also with a wide lens, because light rays are more parallel....

    Back to my original question in above original post; which 75mm lens would be optimum in regards to sharpness and thus give me no diffraction at f/11, thus higher resolving than my 75mm Nikkor SW?

    Thanks!

    Anders

  6. #6

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    Re: Sharp 75mm (no diffraction) ???

    Chris Perez and Kerry Thalmann tested one Nikon SW 75mm f/4.5 as part of their LF film lens tests (using TMX B&W film at 1:20 magnification) and noted significantly reduced center resolution at f/11 versus smaller apertures. Rodenstock and Schneider 75mm lenses fared better. See:

    http://www.hevanet.com/cperez/testin...5mm_thru_125mm

    Of course, all of this is based on single samples of each lens type, so YMMV.

  7. #7

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    Re: Sharp 75mm (no diffraction) ???

    The only choice to do what you want are digital lenses. They don't all have small image circles. The Rodenstock Apo Sironar Digital series have image circles up to 150mm in diameter. They are made specifically for what you are trying to do. Go to the Linos Rodenstock Precision Optical web site and download their white papers on digital optcs and you will get your answers.

  8. #8

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    Re: Sharp 75mm (no diffraction) ???

    Whats the resolution of the digital system youre using the lens on?

    f/11 is the diffraction limit for the Canon 20D, 30D, 5D Mk II etc, anything with a ~6.4 micron resolution.

    Quote Originally Posted by Lynn Jones View Post
    Hi HK

    I have my suspicians. If this lens isn't designed for digital (field flatening for example) then the losses will be quite substandial while not remarkable for a 150mm.

    Sensors require light rays to be perpendicular to their face. Angular rays that are off by a few degrees are not recorded or at best partially recorded. That is why all early digital cameras (except Olympus) lost 30% to 40% of their image resolution. Over time, first Olympus, then Sony, then Tamron, and finally the rest realized that field flatening elements were required for effective use of digital optics.

    If you add to this that "superwide" lenses were optimized for 1:1 and could not be used effectively for focus distances farther than the hyperfocal distance then horrendous field curvature problems occur.

    Lynn
    I have to say Olympus lenses are pretty good, I have an old Zuiko prime that fully exceeds a 6.4 micron resolution at f/5.6.

  9. #9

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    Jul 2008
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    46

    Re: Sharp 75mm (no diffraction) ???

    @ Eric,

    As I expected, Rodenstock and Schneider 75mm is better than Nikkor 75mm. The 75mm lenses tested appear to have not been the f/4.5-5.6 versions and which my instinct tells me should be even better?


    @ Bob,

    I much appreciate your knowledge. What I look for is still sharp traditional 75mm lenses. How do the Rodenstock older and newer such compare to the Schneiders? - example to this one http://www.kenrockwell.com/schneider/75superangulon.htm

    Further, http://www.linos.com/pages/no_cache/...7df0f#sid13372 state the lenses you suggested are recommended for up to 72x96mm and there is no 75mm such. Thus they are out for my up to 44x118mm stitches. I also use my lenses for 4x5 film, thus digitars are out of question due to too small image circle. My Rodenstock Sironar-N is excellent, very sharp also for my Aptus 65 and cost me only 400 usd on Ebay.

    Anders

  10. #10

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    Re: Sharp 75mm (no diffraction) ???

    Quote Originally Posted by Anders_HK View Post
    @I much appreciate your knowledge. What I look for is still sharp traditional 75mm lenses. How do the Rodenstock older and newer such compare to the Schneiders? - example to this one http://www.kenrockwell.com/schneider/75superangulon.htm

    Just as well with most and surpass them with others

    [Further, state the lenses you suggested are recommended for up to 72x96mm and there is no 75mm such. Thus they are out for my up to 44x118mm stitches. I also use my lenses for 4x5 film, thus digitars are out of question due to too small image circle. My Rodenstock Sironar-N is excellent, very sharp also for my Aptus 65 and cost me only 400 usd on Ebay.

    Anders
    The 70mm Apo Sironar Digital covers a 125mm circle.
    Unfortunately you have the requirements of a digital lens and the budget for a used lens. In that case you will not be able to solve your problem with analog lenses.

    I can't give you the Digitar image circles as we are not involved with them. But Rodenstock does make digital lenses with large enough image circles for what you need. They also make digital lenses with image circles too small for your needs. Why don't you contact a dealer and rent a couple to see what they can do? Or at least visit a dealer with a demo studio to see the performance gains?

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