henryberkins Posted January 29, 2007 Share Posted January 29, 2007 recently pondering focal length conversion and came upon a question. a sigma 10-20mm with 1.5 times conversion gives you a 15-30mm combo. how do we get another 5mm?(this may seem stupid) but how does it work? other than the obvious math, will zoom be faster in and out?(i know this is stupid) just thoughts please.... chris Link to comment Share on other sites More sharing options...
oceanphysics Posted January 29, 2007 Share Posted January 29, 2007 It works the same way taking a pair of scissors to a piece of film does. Link to comment Share on other sites More sharing options...
ott_luuk Posted January 30, 2007 Share Posted January 30, 2007 The focal length is a property of the optical design and it`s absolutely independent of the camera you use it on. A 10-20mm lens is always a 10-20mm lens and you don`t get any extra millimeters. The 35mm/full frame equivalent numbers (15-30mm in your case) are merely used to illustrate the field of view on a small sensor camera because people have become used to thinking about focal lengths in terms of the 35mm film frame. BTW did you try to google your question? It took me about 3 sec to come up with this link: http://www.luminous-landscape.com/tutorials/understanding-series/dslr-mag.shtml just read it Link to comment Share on other sites More sharing options...
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