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?