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  1. #21
    AgX
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    Quote Originally Posted by Dan Fromm View Post
    Usually small? Perhaps, but not always. Consider the 8-64/1.9 Angenieux 8x8B as was supplied with the Beaulieu 4008ZM. It t stops around t/3.3. Mine taught me to check all of my cine camera zooms for transmission, against the evil day when the camera's on-board meter failed.
    This is a difference of 1 1/2 stops!!

  2. #22
    Ian Grant's Avatar
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    Quote Originally Posted by AgX View Post
    This is a difference of 1 1/2 stops!!
    Well some of those early Zoom lenses on cine cameras had rather a lot of elements so even with coating there was still quite a significant loss of light, prior to coatins they weren't practical at all.

    Ian

  3. #23
    AgX
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    The Angenieux 10-150mm f2 had a loss of 1/4 stop.

  4. #24

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    I Have a 50mm T2.2 Taylor Taylor Hobson which you can have for $1500: it's attached to a Bell and Howell Foton in excellent working order.

    David. I use f stops, the T stop thing in still photography is hype.

  5. #25
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    Is there any database online of legacy lens T-stop ratings?

    This makes me wonder about my Canon 70-200 2.8 USM IS Mark II as its a beast and I have hear that though it is a 2.8 the amount of glass cuts down on light throughput. Hmmm... Wonder what the T stop is on that baby...


    ~Stone

    Mamiya: 7 II, RZ67 Pro II / Canon: 1V, AE-1, 5DmkII / Kodak: No 1 Pocket Autographic, No 1A Pocket Autographic | Sent w/ iPhone using Tapatalk
    ~Stone | "...of course, that's just my opinion. I could be wrong." ~Dennis Miller

  6. #26
    AgX
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    See my remark two posts above.

    Dan's figure is total out of proportion and so far I got no idea how it could be reasoned. To evalute the transmission, have a look at the schematic of a lens, count the air/glass surfaces and make a calculation of the reflection loss. Any other loss could only be caused by the absorbtion of the glass.

  7. #27
    StoneNYC's Avatar
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    Is there any database online of legacy lens T-stop ratings?

    Quote Originally Posted by AgX View Post
    See my remark two posts above.

    Dan's figure is total out of proportion and so far I got no idea how it could be reasoned. To evalute the transmission, have a look at the schematic of a lens, count the air/glass surfaces and make a calculation of the reflection loss. Any other loss could only be caused by the absorbtion of the glass.
    Umm this is WAY beyond my understanding, I don't know how to do any of that or even what it all means in terms of "figuring it out" I'll just keep an eye out for the statistic, but thanks for trying to help the uneducated...


    ~Stone

    Mamiya: 7 II, RZ67 Pro II / Canon: 1V, AE-1, 5DmkII / Kodak: No 1 Pocket Autographic, No 1A Pocket Autographic | Sent w/ iPhone using Tapatalk
    ~Stone | "...of course, that's just my opinion. I could be wrong." ~Dennis Miller

  8. #28

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    Quote Originally Posted by AgX View Post
    See my remark two posts above.

    Dan's figure is total out of proportion and so far I got no idea how it could be reasoned. To evalute the transmission, have a look at the schematic of a lens, count the air/glass surfaces and make a calculation of the reflection loss. Any other loss could only be caused by the absorbtion of the glass.
    Well, I measured. With K40, daylight filter, known good exposure meter. Understand, the 4008 has a variable shutter, I used Beaulieu's table of shutter speeds given fps with the shutter full open. Yes I shot the test footage with the filter full open. FPS measured by shooting a couple of hundred frames of a digital watch. My 4008 ran on speed at 18 and 24 fps, a couple of frames slow at 70. I got good exposure only when I overexposed (using the aperture, not fps, to control exposure) by a stop and a third.

    I did the same with a Nikon R-10 whose nominal f/1.4 zoom t/stopped around t/2.8. And this is consistent with published tests. Its really usable only at high noon.

    Surprisingly, with the same tests the 6-66/1.8 Schneider on my ZM2 and 6-70/1.4 Schneider on my 5008 both t/stop at their published f/stops, i.e., are faster than claimed. This is also consistent with published tests. And believe me, after a catastrophe with the 4008 (exposure system failed on a shoot and I didn't know what it t/stopped at) I tested every one of my cine cameras with manual aperture setting so I could, if necessary, use an external meter.

    If you haven't done the testing, don't grumble about my results. If you did parallel tests and got different results, that's very interesting, please tell me more.

    Your calculations depend on assumptions about loss/air-glass interface. Why do you believe your assumptions?

  9. #29
    AgX
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    Dan, I said

    Dan's figure is total out of proportion and so far I got no idea how it could be reasoned.
    Both is still true.
    I did not know about any measuring you did, nor would I have doubt them, nor doubt I them now.

    I beg your pardon that my statement/wording caused same aggrevation, that was not my intent.


    Your calculations depend on assumptions about loss/air-glass interface. Why do you believe your assumptions?
    That hint of being out of proportion as well as at self calculating was directed at Stone and his doubt about his modern Canon lens. So far rough calculations based on published typical reflection losses per surface ended in magnitudes of loss coherent with T-values of modern lenses. Furthermore there are statements from the industry including an old one by a Angenieux designer stating a loss factor for the geometrical f-stop of 1.1 .
    Last edited by AgX; 02-08-2013 at 02:19 AM. Click to view previous post history.

  10. #30

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    I take sort of the same position as AgX does - I'm astounded that two lenses Dan mentioned have t-stops implying that only about 30% of the light entering actually contributes to the image.

    I don't doubt that Dan has to do what he says, based on his tests; my reservations are in the presumption that it is strictly a t-stop issue. Dan says, "If you haven't done the testing, don't grumble about my results." My counter to this is, I know how the standard (effective 1964 and 1969) says to test, and he didn't do it that way.

    I can't say with any certainty what might be the reason for the large difference between f-number and t-numbers, but if I had to find out, I'd start by measuring (roughly) the focal length, then the actual aperture diameters. A discrepancy here could go a long way toward explaining the issues.

    I'm glad I don't have one of those lenses, 'cuz I'd have a hard time sleeping 'til I found out why they work that way.

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