Smaller format zooms more efficient
Posted 29 March 2011 - 07:51 PM
For example the Fujinon 5.5-88mm that came with my 1/3" camera is a T1.4. I've seen 16mm Angenieux zooms under T2. Yet when you get to 35mm T2 is about as fast as you can get for a zoom.
Is it just because more glass is needed to cover the sensor and more glass equals more light loss? Or is there something more to it than that?
Posted 29 March 2011 - 11:11 PM
Equally important is the fact that you need some depth of field to shoot. Imagine pulling focus at ultra-telephoto t1.4 on super35. No one could do it! I assume it would be possible to make a t1.4 zoom for super35, but it would be incredibly expensive and probably have rather poor image quality (flare, spherical aberration, etc.) and be almost unusable in terms of size.
You'll notice it's the same with stills. For 35mm still cameras you usually get primes in the f1.4 range; for 6x7 and 6x6 cameras f2.8 is about as fast as it gets; for 4x5 and 8x10 f5.6 is fast (f2.8 exists and by most accounts is amazing), for ULF Schneider makes f11-f22 lenses. The limitation seems to be related to the size of the front element and depth of field. Despite normal aperture values of f16-f64, focusing in 4x5 is an art and a science.
This is mostly second hand and maybe full of fuzzy science. I have a book on lens design but am scared to read it. It's full of real science. I'm just repeating what I've been told and have found from experience.
Edited by M Joel Wauhkonen, 29 March 2011 - 11:15 PM.
Posted 03 April 2011 - 07:41 PM
What is the title of that book on lens design? I would like (to try) and read it and see if I can get a better understanding of why things are the way they are.