What is the widest T Stop possible We are having f stops of below even 0.7 NASA lenses What will be the T stop of such lenses with f stop below ONE?
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.