Archived posting to the Leica Users Group, 2000/11/09
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clive sanbrook jotted down the following:
> Their lenses (say 80 and 150 mm respectively) have a respective depth of field
> shallower than our 'standard' 50 mm lens. but the same as (respectively) our
> 80 and 150 mm lens i.e a 50mm 'wide angle' on MF has the same depth of field
> as a 50mm lens for 35mm cameras (one thing where leica can be no better or
> worse than any other maker ;-^()
No, the above is wrong in just about every respect. Check out:
http://www.outsight.com/hyperfocal.html#nearfar
http://www.reflectiveimages.com/depthoffield.htm
Input: 35mm film, 50mm lens, f/4, 50" distance: DOF 5.9"
Input: 645 film, 50mm lens, f/4, 50" distance: DOF 9.9"
Input: 6x6 film, 50mm lens, f/4, 50" distance: DOF 11.8"
Input: 35mm film, 150mm lens, f/4, 50" distance: DOF 0.6"
Input: 645 film, 150mm lens, f/4, 50" distance: DOF 0.9"
Input: 6x6 film, 150mm lens, f/4, 50" distance: DOF 1.2"
By comparison:
Input: 35mm film, 50mm lens, f/4, 50" distance: DOF 5.9"
Input: 645 film, 64mm lens, f/4, 50" distance: DOF 5.9"
Input: 6x6 film, 70mm lens, f/4, 50" distance: DOF 5.9"
(80mm on 6x6 gives DOF of 4.4"; 80mm on 645 gives a DOF of 3.7")
The numbers for 4x5", 5x7", or 8x10" are left as an exercise for the reader
;)
Conclusion: The 80mm standard lens for 6x6 and 645 DOES have a shallower DOF
than the 50mm lens on 35mm film: the equivallent (for DOF purposes) would be
70mm for 6x6 and 64mm for 645 film. However, the differences are small and
in practice (and by advertisers) the focal lengths are considered equal.
However, the same focal lenth lens on 6x6 or 645 film DOES NOT have the same
DOF when projecting an image on 35mm film. All other things being the same,
image magnification is different, hence DOF is different.
M.
- --
Martin Howard | "...key features are the distinctive rear
Visiting Scholar, CSEL, OSU | lighting clusters that make the Maserati
email: howard.390@osu.edu | 3200GT instantly recognizable to anyone
www: http://mvhoward.i.am/ | overtaken by it." -- Maserati sales lit.
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