Here's a post that I did over on the Olympus-Pen-RF list on that subject:
Mathamatically, I assumed that the "real" factor was related to the diagonal
of the film format, which is the hypotenuse of the thus-formed right
triange. So here are the diagnoal calcs:
Horiz Vert Diagnal Factor
24 36 43.3
18 24 30.0 1.44
The 1.44 factor is then used for all conversions. I've seen magazines use
2x as the factor; but by emperical observation, that isn't right. 70mm
lenses operate much as a 100mm lens on my OM's, and my calculations validate
this observation:
Pen FT FL 35mm Equiv "Standard" 35 lens FL
20 29 28
25 36 35
38 55 50
40 58 50
42 61 50
60 87 85-90
70 101 100
100 144 135
150 216 200
250 361 300-400
400 577 600
800 1,154 1000
50-90 72-130 75-150
100-200 144-288 150-300
I also inserted my opinion of the best match between the Pen F/FT lenses and
"standard" focal lengths commonly offered sith 35mm SLRs. IMO, this
validates Olympus' selection of the focal lengths as directly relating to
35mm and probably they used the same FOV from common 35mm lens lines of the
time (as established by German mfgrs) to arrive at their line up.
But LOOK at the big honking FL on the 800: 1,154mm! During the 70's there
were other 35mm SLR Mfgrs that brought out these big lenses in catadioptric
format. I think I remember seeing Nikon, Canon, Pentax, Contax, and Minolta
all with an offering along the lines of a 1000/11 mirror lens.
Skip
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***********************************************************
From: DBellamy2k@xxxxxxx
Reply-To: olympus@xxxxxxxxxxxxxxx
To: olympus@xxxxxxxxxxxxxxx
Subject: Re: [OM] Pen FT #2606
Date: Tue, 31 Jul 2001 15:27:16 EDT
In a message dated 31/07/01 17:44:03 GMT Daylight Time,
owner-olympus-digest@xxxxxxxxxxxxxxx writes:
<< | The OM lenses will work as longer effective focal length when on the
Pen,
| but I'm not sure if its double. >>
Won't it be more like x1.4 or so, since half-frame is half the area? Your
half frame is, what, 18 x 24 instead of 24 x 36 isn't it? You're getting
about two thirds to three quarters the field of view then, effectively in
each dimension, if you compared two 'landscape' orientation shots, say.
Dave Bellamy.
http://members.aol.com/synthchap/
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