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Thread: How to test lens transmission

  1. #21
    Nodda Duma's Avatar
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    Re: How to test lens transmission

    Quote Originally Posted by swmcl View Post
    .

    (I think I'm right ...)

    :-)
    Yep, and it's a really easy way to get the answer, too.
    Newly made large format dry plates available! Look:
    https://www.pictoriographica.com

  2. #22

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    Jun 2010
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    Red face Re: How to test lens transmission

    Quote Originally Posted by desertrat View Post
    Several years ago I saw a post at another photographic forum, I think the poster was Richard Knoppow, stating that the optical glass made before world war two was "filthy" by modern standards.

    Later on I downloaded and read a book on lenses in the early 20th century, I think it was by Hans Harting, translated into English. He stated that thick lenses like cemented quadruplets and quintuplets absorbed an appreciable amount of light and slowed the whole lens system down somewhat.

    I rigged up a test fixture using an old American Optical research style microscope illumination lamp with condenser and iris, and a Weston Master exposure meter for the sensor. The light pencil was made small enough so all of it would reach the sensor.

    My test subjects were a Wolly RR, an old uncoated Dagor, and a Turner-Reich triple. All of these lenses have 4 air-glass interfaces. The meter readings were taken before and after the lens was inserted in the light path.

    The RR absorbed a small amount of light, a small fraction of a stop. The Dagor absorbed a little more. The T-R triple absorbed a whopping stop and a half, roughly.

    Unfortunately I can't find the piece of note pad paper I scribbled the readings on.
    Post in haste, repent at leisure...

    The RR had beautiful glass, like new, and the cemented doublets were pretty thin. Most of the difference in meter readings was probably due to loss from reflections at the air/glass interfaces, and very little due to absorption.

    The triplets in the Dagor were a little thicker, so the difference in readings after inserting the lens in the light path between it and the RR were probably due to absorption. Most of the absorption was probably occurring in one of the cement layers in the front group which is a bit hazy. A pristine uncoated Dagor might have given readings almost the same as the RR.

    The T-R was a late uncoated one, the cemented quintuplets were very thick, and the light was passing through a lot of glass. I think most of the stop and a half loss was due to absorption.

  3. #23

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    Re: How to test lens transmission

    Thanks for all the info!

  4. #24

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    Re: How to test lens transmission

    Quote Originally Posted by swmcl View Post
    When the lightmeter reads the same for both lenses the amount of light is the same. ie the aperture is the same.

    (I think I'm right ...)

    :-)
    I think it would be the same aperture as measured in T-stops, not F-stops. Not much difference if the lenses are similar, maybe a bigger difference if one is a 13 element zoom lens for 35mm/digital and the other is a Landscape Meniscus.

  5. #25
    ic-racer's Avatar
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    Re: How to test lens transmission

    Quote Originally Posted by Randy Moe View Post
    Ha, you found my old nickname from my early motorbike years.

    'Madman Moe' LOL AKA '10 Grand' as I always shifted at 10K revs. New Hondas were something.

    I dislike old electronics. They alway fail. I collected tube radios since the 50's when I was a kid. I have plenty of non-working old electric gear. I made my own pirate radio station in 1966.

    I'll trade a you Wire Recorder, which precedes Tape recorder.

    As for collecting. I have less than 5% of my former collections.

    Now will you answer my question?

    Do you see significant, more than 20% variation, in lens transmission from lens to lens? As measured by the old Horse?
    My brother still has his Atwater Kent collection he put together in the 1970s.
    You may not know this but the Horseman exposure computer has no aperture markings. It indicates only the appropriate shutter speed for the light that would fall on the film. Utility of the device is realized best with bellows extension, unmarked lenses, improper or missing aperture scale and sloppy aperture mechanisms.

  6. #26
    Tin Can's Avatar
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    Re: How to test lens transmission

    Quote Originally Posted by ic-racer View Post
    My brother still has his Atwater Kent collection he put together in the 1970s.
    You may not know this but the Horseman exposure computer has no aperture markings. It indicates only the appropriate shutter speed for the light that would fall on the film. Utility of the device is realized best with bellows extension, unmarked lenses, improper or missing aperture scale and sloppy aperture mechanisms.
    I'll add one to my wish list.

    Not kidding.

    Thanks!

    I just got a pair 60's Shure Vocal Master 6 foot tall speakers. The amp is solid state, NG, but my old system now sounds fantastic with 12, low watt speakers. $20, well spent.
    where is the monolith

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