Why do stills-oriented lenses use f-stop instead of t-stop?

This is possibly a dumb question, but it's been bugging me for a few weeks. I've seen several references to the Sigma Art lenses as being "dark" for their f-stops, probably due to the fancy coatings on the glass. I've also seen that cine lenses are sold by t-stop, which seems to make more sense to me - doesn't it matter more how much light actually gets through, especially since that's the only way you can really keep the same aperture/ shutter/ ISO settings when you swap lenses?

Just curious.

Because stills orientated lenses in general do not need to consistantly get exposure correct to such a high degree of accuracy that can be had by using a set of T-stop lenses.

Well that makes sense for why cine lenses need t-stop, but it doesn't explain why stills lenses continue to use f-stop. What advantage is there to f-stop?

The f-stop advantage is the lens costs less and your depth of field calculations will work.

LonelyBoy wrote in post #17503446
Well that makes sense for why cine lenses need t-stop, but it doesn't explain why stills lenses continue to use f-stop. What advantage is there to f-stop?

T-stops give some indication of exposure whilst f-stops will provide indication of DoF....the later is more relevant to still images.

Bob

Canon Bob wrote in post #17503992
T-stops give some indication of exposure whilst f-stops will provide indication of DoF....the later is more relevant to still images.

Bob

+1, this is correct. One critical thing to understand is that the light loss in modern lenses is tiny, well under 1/3 stop because the coatings are so good these days. So to mess around with T-stops is asking for a level of precision in light transmission that isn't of much importance in still images.

JeffreyG wrote in post #17504092
+1, this is correct. One critical thing to understand is that the light loss in modern lenses is tiny, well under 1/3 stop because the coatings are so good these days. So to mess around with T-stops is asking for a level of precision in light transmission that isn't of much importance in still images.

Except when you add some filters. A lens set at f/2 with a 2 stop ND filter mounted will give a 4 T-stop combination that's still f/2 optically.

Bob

Thanks all! It hadn't sunk in that DoF only cared about f-stop. Now it makes sense.