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Thread: explain like I'm 5......... 90mm lenses

  1. #21
    Alan Klein's Avatar
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    Re: explain like I'm 5......... 90mm lenses

    Jpseph, I have a Chamonix 4x5. How does the f/8 rating of the Nikkor 90mm rate as far as ability to see the GG that has a fresnel lens? Would this be a good selection for 4x5?

  2. #22
    Alan Klein's Avatar
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    Re: explain like I'm 5......... 90mm lenses

    Why do 75mm and 90mm have the same 105 degree angle of coverage based on this sheet from references in this forum?
    https://www.largeformatphotography.i...s/LF4x5in.html

    Where can you get dimension spec (length width etc) for all lenses?

  3. #23
    Alan Klein's Avatar
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    Re: explain like I'm 5......... 90mm lenses

    Th aforementioned sheet of lenses shows center filter prices for many of the lenses. WIll I need to buy this separately if listed? I shoot Tmax BW and color slide film.

  4. #24

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    Re: explain like I'm 5......... 90mm lenses

    Quote Originally Posted by Alan Klein View Post
    Why do 75mm and 90mm have the same 105 degree angle of coverage based on this sheet from references in this forum?
    https://www.largeformatphotography.i...s/LF4x5in.html

    Where can you get dimension spec (length width etc) for all lenses?
    That’s the angle of illumination, not the angle of coverage. The first determines how large a diameter the lens covers. The second is how wide the lens is on the format you are using. So an 105° coverage lens has a larger circle of illumination then an 80° coverage lens.

  5. #25
    Tin Can's Avatar
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    Re: explain like I'm 5......... 90mm lenses

    Look at this image made with a tiny lens

    I have one of these lenses and plan to use it more

    https://www.largeformatphotography.i...=1#post1535231
    wear mask or NOT

    is ???

  6. #26

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    Re: explain like I'm 5......... 90mm lenses

    Hmm. Randy, if you want tiny, you want a 90/14 Perigraphe VIa. Compared to it the 90/6.8ers are monstrous. However, the Perigraphe is in barrel. Stuffed into the front of an Ilex #3 -- that's how I use mine -- it isn't quite so small. But with a Speed Graphic, ...

  7. #27
    Corran's Avatar
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    Re: explain like I'm 5......... 90mm lenses

    Quote Originally Posted by Tin Can View Post
    Look at this image made with a tiny lens

    I have one of these lenses and plan to use it more

    https://www.largeformatphotography.i...=1#post1535231
    It may be instructive to consider the movements used here. With some front rise to correct keystoning, the bottom of the lens' image circle is being cut off, showing good sharpness therefore in the lower area of the image. In opposition, the poorer area of the image is being almost completely hidden in a dark featureless sky. There may even be some vignetting we don't see. This image is an example of an absolute best-case scenario for the Optar.

    In other scenarios the corner areas may be unsuitable. I also have one negative that I noticed better performance than expected in the bottom area which I think is indicative of field curvature, which in some cases is actually helpful.

    Other than some "golden" samples, I would guess any and all small f/6.8 90mm lenses of the Angulon/Optar variety would perform relatively worse than newer and larger lenses, but that may very well not matter to some and for some applications.
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  8. #28

    Re: explain like I'm 5......... 90mm lenses

    Quote Originally Posted by Alan Klein View Post
    Why do 75mm and 90mm have the same 105 degree angle of coverage based on this sheet from references in this forum?
    https://www.largeformatphotography.i...s/LF4x5in.html

    Where can you get dimension spec (length width etc) for all lenses?
    The Fujinon f/8 lenses are 100 degree angle of coverage - the angle of coverage is inherent in the design of a particular lens. For a given angle of coverage, the diameter of the image circle increases linearly with the focal length. Assuming no mechanical vignetting, to calculate the diameter of the usably sharp image circle, a good approximation is 2 x the tangent of (angle of coverage/2) X focal length.

    Lens data and manufacturer specs are basically found throughout the Internet - there are very few new LF lenses being manufactured. This forum is a good place to start, particularly the sticky items at the top. Dan Fromm's guide to lens data can be found on this forum and is likely the best starting point.

  9. #29

    Re: explain like I'm 5......... 90mm lenses

    Quote Originally Posted by Alan Klein View Post
    Why do 75mm and 90mm have the same 105 degree angle of coverage based on this sheet from references in this forum?
    https://www.largeformatphotography.i...s/LF4x5in.html

    Where can you get dimension spec (length width etc) for all lenses?
    i have not found that an f/8 lens is significantly more difficult to view on the ground glass, but size and bulky may be of greater operational importance to some. On a smaller wooden camera ( I have a Nagaoka 4x5 myself), the bulk and weight of an f/5.6 may be too much for the front standard or simply too large and heavy to be comfortable in operational use. Your mileage may vary. I do find that a fresnel lens is very helpful at the corners.

  10. #30
    Alan Klein's Avatar
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    Re: explain like I'm 5......... 90mm lenses

    I just got an idea. I have an f/5.6 150mm. I'll turn the aperture down to f/8 while viewing and see how bright it is to help make a decision about my next lens.

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