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Thread: Large Format Focal Plane Meter - New Product

  1. #21

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    Re: Large Format Focal Plane Meter - New Product

    Quote Originally Posted by faberryman View Post
    I do not know of any 50mm lens for large format, certainly none that would focus with 300mm of bellows extension. But that is just my world.
    There are plenty. I'll just mention a few that I have. Here is my Mamiya 37mm f4.5 fisheye -- makes absolutely, unbelievable close-up shots:

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    Here's still more, among them a Minolta 12.5mm f2.5, a Minolta 25mm f2.0, and a Minolta 50mm f3.5. I've used all of them with more than 300mm of extension:

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    Then there's my Schneider 47mm XL f5.6 and Fujinon SWD 65mm f5.6 that I've used with long extensions at times, but I think I've made my point. Happy spot metering -- when it's appropriate, which isn't too often, I use a Minolta Autometer II with 5 degree spot attachment.

  2. #22

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    Re: Large Format Focal Plane Meter - New Product

    Of the six lenses you mentioned only one is a 50mm lens - the Minolta 50mm f3.5. Is that a large format lens or an adapted lens? What is its image circle? What is the focus distance with 300mm of bellows extension?

  3. #23

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    Re: Large Format Focal Plane Meter - New Product

    Quote Originally Posted by faberryman View Post
    I do not know of any 50mm lens for large format, certainly none that would focus with 300mm of bellows extension. But that is just my world.
    45mm and 55mm Apo Grandagon.

  4. #24

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    Re: Large Format Focal Plane Meter - New Product

    Quote Originally Posted by faberryman View Post
    Of the six lenses you mentioned only one is a 50mm lens - the Minolta 50mm f3.5. Is that a large format lens or an adapted lens? What is its image circle? What is the focus distance with 300mm of bellows extension?
    Yes, only one is 50mm. You've got me there! I just chose that, at random, as an example, but FOUR of the lenses I mentioned have focal lengths SHORTER than 50mm. FYI, microscopic lenses are used on large format cameras all the time. Only two of mine are microscopic lenses, but at high magnifications -- which these lenses are designed for -- large formats (in my case, 4x5) are completely covered. And by the way, the results are amazing -- and metering with flash is easy when metered of off the ground glass. No need to try to make a spot meter reading of a moth's wing.

  5. #25

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    Re: Large Format Focal Plane Meter - New Product

    Quote Originally Posted by xkaes View Post
    Yes, only one is 50mm. You've got me there! I just chose that, at random, as an example, but FOUR of the lenses I mentioned have focal lengths SHORTER than 50mm. FYI, microscopic lenses are used on large format cameras all the time. Only two of mine are microscopic lenses, but at high magnifications -- which these lenses are designed for -- large formats (in my case, 4x5) are completely covered. And by the way, the results are amazing -- and metering with flash is easy when metered of off the ground glass. No need to try to make a spot meter reading of a moth's wing.
    What is the distance between the lens and the moth's wing?

  6. #26
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    Re: Large Format Focal Plane Meter - New Product

    Quote Originally Posted by Dave Gooding View Post
    However, as a non-photographer myself I am open to advice on whether a +/- 4 stop range around the nominal exposure is sufficient to capture the full reproducible range of the film.
    That is not sufficient - it's far short of the range that many negative films can record. Whether the output medium is so limited is irrelevant, as photographers often face the task of assessing subject brightness ranges that far exceed that and figuring out how best to record them on film for later interpretation in the darkroom or image editor and translation to a chosen output medium. Unless there is a compelling engineering reason to do so, you should not arbitrarily truncate the range - provide as much as the components will allow, and let the user decide how to apply that capability to the metering tasks at hand.

  7. #27

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    Re: Large Format Focal Plane Meter - New Product

    Quote Originally Posted by Oren Grad View Post
    That is not sufficient - it's far short of the range that many negative films can record. Whether the output medium is so limited is irrelevant, as photographers often face the task of assessing subject brightness ranges that far exceed that and figuring out how best to record them on film for later interpretation in the darkroom or image editor and translation to a chosen output medium. Unless there is a compelling engineering reason to do so, you should not arbitrarily truncate the range - provide as much as the components will allow, and let the user decide how to use it.
    Thanks. what sort of range can a film sensibly cover? I did run a series of 20 or 30 test exposures on Ilford HP5 as part of a calibration exercise (to calibrate a sensor against which each unit is checked and adjusted). I measured the negative intensity and plotted it against exposure. It follows an S-curve with a roughly linear region of +/- 4-ish steps in the middle but there are measurable intensity differences between consecutive exposures even at 10 stops away from the nominal, although to the eye these extreme ones have no discernible difference. Would you really operate the film at these extremes?

    The scale is a trade off between allowing accurate estimation of fractional-stop variations and giving enough range. Going to +/- 5 or 6 would be no problem but at +/-10 you'd be peering at a finely-spaced scale and struggling to see quarter-stop differences.

    A +/-4 range implies you are covering a range of 256x in the brightness between deepest shadow and brightest highlight - and getting the detail in these regions - in the same print. +/-6 implies a factor of 4000 across the image. Is this really true? Obviously if it is the case then I need to expand the range since it is exactly these scenarios this meter is intended for!

    I'll find my film exposure test data and post it here.

  8. #28

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    Re: Large Format Focal Plane Meter - New Product

    Here are the results from my calibration test exposures.
    I inserted a meter sensor in the back of the camera and measured its output at a given aperture when aimed at a grey test card in near-uniform illumination. I then ran a series of exposures at different exposure times without changing the aperture or the set up. I then measured the opacity of the developed negatives, plotted them out and thus determined the calibration data for the sensor I used during the test run. This particular sensor was then retained and is used for the check and calibration of each meter produced.
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  9. #29

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    Re: Large Format Focal Plane Meter - New Product

    Actually looking at this again I think I must agree that +/-4 is no enough and I should at least go to +/-6, more if other films give a better range.
    The advice I had when I designed the meter was that +/-3 was enough but I think that was based on the print range rather than the film.
    Any other opinions before I amend the design? I'll retrofit any mod into my stock as it is a very simple thing to do.

  10. #30

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    Re: Large Format Focal Plane Meter - New Product

    Quote Originally Posted by faberryman View Post
    What is the distance between the lens and the moth's wing?
    I can tell you've never used a microscope, and apparently have done little macro work either. In MANY microscope situations, the subject and the lens are so close that oil is used to connect then together. I could photograph a butterfly's wings with a distance of 1 inch to 1/10 of a millimeter between the two. If you've got a spot meter that can somehow fit in there, PLEASE tell the photographic world!

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