How low can a lens T-stop go, and how does it relate to very fast f-stops?
Asked 10/23/2015
5 views
2 answers
0
I’ve seen references to lenses faster than f/1, including specialty or "NASA" lenses around f/0.7. What would the corresponding T-stop be for lenses with an f-stop below 1? Is there a practical lower limit, and what’s realistically available in consumer photography versus scientific or industrial optics?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
10y ago
2 Answers
1
Depends what you want? Photolithography lenses are sitting around f/0.6 consistently these days and they have almost perfect transmission, so t/0.65 or so. You can buy microscope objectives faster than f/0.4 these days as well, though they require immersion oil to function. These systems again have very fast t/#s. In the consumer marketplace? t/1.2 is about as good as you will do with some of the very fast cinema lenses, or a used Canon 50mm f/1.0L which should be around t/1.1-t/1.2 or so. Most of the f/0.95 lenses available are probably closer to f/1.05 and have strong losses, so t/1.1 would be about right.
Originally by user40937. Source · Licensed CC BY-SA 4.0
user40937
10y ago
0
Generated from our catalog & community — verify before relying on it.
T-stop measures actual light transmission, while f-stop is a geometric ratio. A lens’s T-stop is always the same as or slower than its f-stop because some light is lost in the glass.
So if a lens is faster than f/1, its T-stop can also be below 1 — but only if transmission is extremely efficient. In specialized optics, very fast systems do exist: photolithography lenses around f/0.6 can have near-perfect transmission, giving roughly T/0.65. Some microscope objectives are even faster than f/0.4, though those are highly specialized and may require immersion oil.
In practical consumer or cine use, the fastest real-world T-stops are much less extreme. Very fast cinema lenses are around T/1.2, and a lens like the Canon 50mm f/1.0L is roughly around T/1.1–T/1.2. Many lenses marketed as f/0.95 transmit more like about T/1.1 in practice.
So there’s no hard rule preventing T-stops below 1, but sub-1 T-stops are mostly found in specialized scientific/industrial optics, not mainstream photography lenses.
Recommended products
UniqueBot
AI10y ago