I pose this question mainly for Tyler Allred, who has actively been using a D100 with both conventional photo lenses, such as the Nikon 70-300/4-5.6, and the Celestron C5, most commonly with the 0.63 reducer that converts the native F10 Schmidt-Cassegrain to f6.3.
F-stop vs. T-stop refers to the relative light transmission. I.e., a lens that is very inefficient, letting through only half the light supposedly it should, would have a T(ransmission)-stop of f8, if the native lens by aperture was f5.6.
So, same scene, say bright sunlight, where at an ISO 100 setting you'd expect the 70-300/4-5.6 to result in an exposure of 1/800, and the f6.3 C5 to give an exposure of 1/640, what is the ACTUAL exposure typically indicated by the D100 for the C5?
Due to the light loss from reflecting off the primary and secondary mirrors, as well as the effect of the central obstruction, I know it has to be slower, but, I'm interested in how much slower, than the 1/640, which allows one to calculate the T-stop of the lens.
Once Tyler has a chance to respond, I'll relate further my experience today shooting a roll of ISO 400 film with a vintage 1983 Sigma 600 mm f8 "mirror" lens, trying to get some shots of a Mute Swan (who likely had escaped from someone's private pond.)
F-stop vs. T-stop refers to the relative light transmission. I.e., a lens that is very inefficient, letting through only half the light supposedly it should, would have a T(ransmission)-stop of f8, if the native lens by aperture was f5.6.
So, same scene, say bright sunlight, where at an ISO 100 setting you'd expect the 70-300/4-5.6 to result in an exposure of 1/800, and the f6.3 C5 to give an exposure of 1/640, what is the ACTUAL exposure typically indicated by the D100 for the C5?
Due to the light loss from reflecting off the primary and secondary mirrors, as well as the effect of the central obstruction, I know it has to be slower, but, I'm interested in how much slower, than the 1/640, which allows one to calculate the T-stop of the lens.
Once Tyler has a chance to respond, I'll relate further my experience today shooting a roll of ISO 400 film with a vintage 1983 Sigma 600 mm f8 "mirror" lens, trying to get some shots of a Mute Swan (who likely had escaped from someone's private pond.)
