fusionrx Posted May 29, 2003 Share Posted May 29, 2003 On the lenses of cameras I see that they have a set of numbers regarding the f-stop. In this case I see the following: Fish-eye lens 1:3.5-4.5 <-- This is what I have questions about, see below 17-28 mm Now, the F-stop has adjustments from 3.5-22. My question is what does the 3.5-4.5 represent? Is that an optimal setting for the lens? Thanks for the help. Dan Magnusson fusionrx@hotmail.com Link to comment Share on other sites More sharing options...
nicol_verheem1 Posted May 29, 2003 Share Posted May 29, 2003 The f3.5-f4.5 is the maximum aperture at the extreme focal lenghts. In your example's case it is not constant, i.e. the maximum aperture at 17 mm will be 3.5, and at 28 it will be 4.5. So the range at 17mm will be 3.5-22, and at 28 it will be 4.5-22 (or maybe 27). If you get amore expensive fixed maximum aperture lens (e.g. the 17-28 F2.8L) the maximum aperture is a constant 2.8 throughout the zoom range. nlv Link to comment Share on other sites More sharing options...
joe_chott Posted May 29, 2003 Share Posted May 29, 2003 I am by NO means an expert, but from what I know, it works like this: 1:2.8 That would mean that the lens has a minimum F stop of 2.8 at all focal lengths (or it could be a prime) 1:3.5-4 That would mean that the lens has a minimum F stop of 3.5 at its minimum focal length and a minimum F stop of 4 at its maximum focal length. In a more concrete example: 17-40mm f/4L This lens has a minimum F stop of 4 at ANY focal length - the minimum is the same for all focal lengths. 28-135mm f/3.5-5.6 IS USM This lens has a minimum F stop of 3.5 at a focal length of 28mm, and a minimum F stop of 5.6 at 135mm. I currently have NO idea how to know (other than trying the lens) what the F stops are for other focal lengths in between the two extremes. Hopefully this helps you. -Joe Chott P.S. If I am wrong on some of this, please, some pro, help me out - I don't wanna steer this guy wrong, but this is the way I understand it. Link to comment Share on other sites More sharing options...
NK Guy Posted May 29, 2003 Share Posted May 29, 2003 What are all these numbers printed on my lens?<P><A HREF="http://photonotes.org/articles/beginner-faq/lenses.html#numbers"> http://photonotes.org/articles/beginner-faq/lenses.html#numbers</A> Link to comment Share on other sites More sharing options...
fusionrx Posted May 29, 2003 Author Share Posted May 29, 2003 Thanks for all the answers! Dan Link to comment Share on other sites More sharing options...
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