T Stops for DSLR 'Video' Lenses?

If this helps...
http://forums.dpreview.com/forums/readflat.asp?forum=1030&message=33785655

Thanks Sem, I do indeed love that thread on DPReview! It's just so full of useful info!. I was wondering why NIKON doesn't publish them?

It would be far more practically useful than them publishing stuff like 'It's got 10 elements in 6 groups!
That's interesting, but hardly useful!

I still don't understand those element / group things.... :) If it says 6 groups I try to count what looks like a group to me but ten I can only count 5 or 4 hehe

Rene, it's all to do with glue...sorry Optical Cement..... ;-)

AFAIK, a Group is a bunch of individual lenses, or Elements, all bonded together.

If it's not attached to another piece of glass, ie it's a single Element, that counts as a Group too!
That makes a Classic Triplet 'lens', a 3 Element in 3 Group Lens! If 2 of those lenses are bonded, it becomes a 3 Elements in 2 groups lens

The VRII Version of the 70-210mm 2.8 is 21 elements in 16 groups. That makes 10 bonded lenses (making 5 groups) and 11 free lenses (making 11 groups). Total 16 groups!

The movie industry which still shoots a lot of film by the way is probably not really interested in shooting with D4/D800 cameras. When movies are shot digitally they tend to use high end cameras such as Panavision and Red.
You sure have a bee in your bonnet about this F/ stop T/ stop thing and Nikon

Michael, just trying to get to the bottom of it! ... More like a dog with a bone ;-)

Were you expecting the 200-400mm f4 to be -0.7EV between f and T stop? or the variation in these Prime Lenses?

AF DX 10.5mm f/2.8D: 85%, T/3.08
AF 14mm f/2.8D: 74%, T/3.29
AIS 28mm f/2: 83%, T/2.19
Zeiss ZF 35mm f/2: 85%, T/2.17
AF 35mm f/2D: 92%, T/2.09
PC-E 45mm f/2.8: 90%, T/2.99
AIS 50mm f/1.8: 95%, T/1.83
AF 50mm f/1.4D: 91%, T/1.48
AF-S 50mm f/1.4G: 91%, T/1.48
AF Micro 60mm f/2.8D: 83%, T/3.11
Hartblei 65mm f/3.5 T/S: 96%, T/3.62
AF 85mm f/1.8D: 81%, T/1.97
AF Micro 105mm f/2.8D: 82%, T/3.13
AF 135mm f/2D DC: 86%, T/2.16
AF-S 200mm f/2G VR: 79%, T/2.24
AF-S 400mm f/2.8G VR: 76%, T/3.25

Thanks to Marianne Oelund for this info.

It makes no difference to me what the T stop on the lenses I use on my DSLR's is. I use TTL metering 99% of the time with them and that takes care of that. When I shoot 4X5 and use my Sekonic meter I have yet to see any issues with exposure. (And I shoot a lot of Chromes)
The bottom of it is simple. F/stops are a mathematical function T stops are a measurement of the light that passes through the lens accounting for the loss at each air glass boundary. The two are probably never the same (Even if Panavision claims that the T stop and F stop is the same on their premo lenses)

High-end video/film lenses have requirements not always met by conventional still camera lenses, even very good ones. These include...

Parfocal performance: the lens stays in focus when zoomed
Long focusing scale, with accurate distance markings
Linear aperture settings (exponential actually, equal rotation between stops)
Geared operating rings for aperture, focus and zoom, to enable external control.
Constant aperture during zoom and focus operations

Some of these features, parforcal operation in particular) require extra elements, which diminish light transmission. "T" stops are simply f/stops which account for these losses. Lens coatings have improved a lot in the last 20 years, much less over the 70 or 80 years in which T-stops have been in use. It is not unusual for these lenses to cost over $100M, and are usually rented rather than purchased by production companies. Schneider introduced a line of "bargain" prime lenses a couple of years ago, in the $50M to $80M range. And I thought Hasselblad lenses were expensive.

Doesn't DSLR video metering continue to be TTL? Doesn't that make this hair-splitting more or less completely irrelevent.