Bill, I can tell the difference between a lens whose aperture doesn't open fully and one whose aperture is stuck. That wasn't the problem.
Angenieux and Nikon have long and good histories. When either specifies a lens' geometrical aperture, I believe what they say.
The R10 might bleed a lot of light off into the viewing optics, since it has an integral beam-splitter, but other S8 cameras with beam-splitters in the light path don't have this problem. Beaulieu S8 cameras (except the 1008 and 1028, which are rebadged Japanese cameras) have mirror shutters, lose no light to the viewing system; with the shutter open the film gets all of the light, with the shutter closed the viewer gets all of the light. As a result, when the camera is running the image in the viewer flickers.
Re what the standard says (and I haven't gone looking for it), given a 4008 ZM with an Angenieux 8x8B, what would you do to get good exposure when the onboard TTL metering system dies? I don't see a better way than testing with narrow latitude film. If there is one, I need to know about it.
Originally Posted by Dan Fromm
Hi Dan, I'd probably do what you did, if I knew exactly how (I'm not a cine guy). Whatever it takes to get good exposures.
The old T-stop standard (1960s) considers the lens alone, measuring light in the center of the field with some sort of photo cell vs a lensless standard. (I don't quite follow the method, they say it's explained in the referenced patent, I linked to similar text earlier this thread.) I doubt it will be any help to you for your purposes.
My only quarrel is with calling the exposure adjustment a T-stop if you don't know for sure which components are causing the issue. If you think the lens is solely to blame, then I still have a hard time believing that the glass in a commercial lens might only let ~30% of the light through.
Bill, I agree with you that a nominal f/1.9 lens that t stops around t/3.3 seems very odd. But K40 doesn't lie. I was very shocked by the disagreement between my 4008ZM and, e.g., my Nikkormat.
As for the R10, well, as I said I'm not the only person to have been surprised by its lens' poor transmission. On the other hand, the lens has several gazillion elements and light is bled for the viewer and for the meter. See http://imaging.nikon.com/history/cou...19-e/index.htm , the lens' cross-section is at the bottom of the page.
Coming back to the original question of this thread:
"Is there any database online of legacy lens T-stop ratings?"
Originally Posted by Les Sarile
This is interesting. I can't remember ever seen T-values indicated for still photography lenses.
What is also interestening is that these figures indicate the same T-factors as given for much more groups containing zoom lenses.
This is common on all the lens reviews I have seen in these older magazines. The first one I posted was from the January 1979 Popular Photography magazine as part of the Minolta XD-11 review. This one is from a newer December 1982 Popular Photography as part of the FM2 which shows a Nikkor zoom. As you can see, the actual T numbers are very close to f numbers marked. I can only imagine that the superb Canon 70-200 f2.8 L lens is as good or better in this regard. Unfortunately, the review of it doesn't show this info nor in Canon's specs. Since the older lenses are for all practical purposes close enough, they probably are no longer concerned about this bit of data anymore.
It's quite an elaborate design, for sure. I would not normally think of a beam splitter as part of the lens, but in these cases it definitely is, so should properly affect the T-stop. I'd guess that the beam splitters are the predominant reasons for light loss, but perhaps only Nikon knows for sure.
Originally Posted by Dan Fromm
Bill, most Super 8 cameras have beamsplitters in the light path. The Nikon R10 stands out among them for light lost between the front of the lens and the film.
Beaulieu S8 cameras (except the 1008 and 1028) have reciprocating shutters with a mirror. With them, when the shutter is open all of the light that the lens passes goes to the film. When the shutter is closed all of the light goes to the viewer; light for the meter is taken from the viewer by a beamsplitter. Y'r explanation doesn't work for these cameras. My dim Angenieux 8x8B was on a Beaulieu 4008 ZM.
Canon's 8.5-25.5/1.0 zoom, as fitted to the Canon 310XL, 310XL-S and AF310XL cine cameras was probably the fastest photographic objective made in (relatively) large numbers. Canon were very serious about making these cameras as usable as possible in dim light. To this end, the 310XL had a non-TTL meter, a relatively slow shutter speed for an S8 camera, and fed light to the viewing optics with a tiny fixed mirror (not beam splitter) behind the lens. If you look at the specs here http://www.canon.com/camera-museum/c...2.html?lang=us you'll see that they assert the 310XL has a TTL meter; this isn't so, the meter is external, with the cell located above the lens.
The search for a T stop database for still photography seems like an answer in search of a question. After you found the information you would then need to find out how accurate all of yor cameras are at the standard shutter speeds and variable speeds. Then you would need to test all of the meters to see how far off they might be. A teacher in High School once told me that if you considered the difference between T stops and F stops and then added in shutter speed variables and chemistry measuring variables and thermometer accuracy variables you would think it's just about impossible to get a good end result. In practice these variables tend to cancel each other out. If you have a lens which was marked with a maximum aperture of f/1.4 but measured T 1/.53 in a particular test, your example might measure T 1.59 or T 1.37. It is probably not practical to test every single lens for T transmission. If this were a serious problem we would have known about it a long time ago. There is the additional issue of the uniformity of the transmission. A fast standard lens will typically have some light fall-off at the corners close to or at full aperture. Should we then measure T transmission at different points of the field of view?