Yes, but you do realize you've switched measurements, right?

by MarkatNite - 3/28/13 5:37 PM

In Reply to: so.. by cawahe

In your first post you asked about "the diameter of the lens ... 58mm thread ... 77mm thread". But now you're asking about "the focal length ... 50mm lens ... 70mm lens".

For example, a zoom lens can vary its focal length, but will always only have one thread size.

Now, as PCC noted, since the f-number is the ratio of focal length over pupil diameter, if two lenses are set to the same f-number (stop) the one with the longer focal length will have a larger pupil diameter.

e.g. 50mm (focal length) / 35mm (pupil diameter) = f/1.4 (approx) vs 70mm (focal length) / 50mm (pupil diameter) = f/1.4

So a 50mm lens at f/1.4 has an entrance pupil diameter (not to be confused with filter thread or exterior lens diameter) of around 35mm, while a 70mm lens at f/1.4 has an entrance pupil diameter (again, not to be confused with filter thread or exterior lens diameter) of 50mm.

And obviously 50mm is larger than 35mm - Mark