Calculating focal length - ist D...

5 posts
17 years
Great Britain

Posted 21/04/2012 - 15:55 Link

Currently having a go at photographing the moon on my ist D using the following combination of lenses: Ricoh 60-300mm (racked out to 300mm most of the time) with a 2x convertor then a 3x convertor (closest to the camera body). If I include the 1.5x focal gain factor (as all these lenses are old manual types (not Di), then what is the total focal length I've got please? - My guess was 300 x 2 = 600mm x 3 = 1800 then x1.5 = 2700mm? Not sure myself! Thanks anyone who can guide me - Anthony.

Frogherder Frogherder

1776 posts
17 years
Burton upon Trent

Posted 21/04/2012 - 16:40 Link

Essentially correct

With a 300mm lens + x2 + x3 the focal length is 300x2x3 = 1800mm

The combination remains at that irrespective of whether it is a 35mm film (full frame) or 2/3 DLSR sensor.
However the visual effect because of the smaller sensor is to imitate a 2700mm lens

regards
Bernard

edwardone edwardone

5 posts
17 years
Great Britain

Posted 23/04/2012 - 18:07 Link

Thank you very much for the explanation Bernard, especially the fact that the image technically stays at 1800mm, with the visual imitation of 2700mm. I hadn't thought of it like that. Thanks - Anthony.