Wonder if that article is in the Archives at View Camera Magazine . I seem to remember they also had a chart of focal lengths and corresponding lengths in other formats.
Here’s how to calculate the equivalent focal length in terms of a familiar format for a different focal length and format.
F = unknown equivalent focal length for the familiar format
D = diagonal of the image rectangle of the familiar format
f = focal length of new format
d = diagonal of image rectangle of the new format
F = f*D/d
Determine the 35mm format equivalent of the Mamiya RZ67 210mm APO lens on the 6 x 7cm format.
Take the diagonal of the 35mm format as D = 43.27mm and the diagonal of the 6 x 7cm format as d = 89.25mm (The Mamiya RZ67 manual states that the format is 56mm x 69.5mm).
F = 210mm*43.27mm/89.25mm = 101.8mm = 102mm to the nearest millimeter
This agrees with the 35mm equivalent for this lens given by Mamiya here
Ian, if I did my math correctly, then a 210mm lens on a 4x5 would be roughly equivalent to 55mm on 35mm camera?
F = 210mm*43.27mm/163mm
I get 163mm diagonal for 4x5 film.
I measured the image window of my 4” x 5” Fidelity Riteway = 92.5mm (between film-holding rails) x 120.1mm.
So the diagonal or the image rectangle is 151.6mm.
Then the 35mm equivalent of a 210mm lens on the 4” x 5" format is
F = 210mm*43.27mm/151.6mm = 59.94mm = 60mm to the nearest millimeter.
This makes sense, since the normal focal length for 4” x 5” format is 150mm.
So yes, you were close. The key idea is to use the diagonal of the IMAGE rectangle—not the size of the film, because that has lots of non-image border.
I'm with Brian Shaw on this one. If you think you can get a head shot with a 210mm lens from 7-10 feet, you haven't tried - it no where close. A commercial photographer I know always used a 12" Dagor on 4x5 for portraits. So I think a little longer lens - in the neighborhood of 240mm to 300mm - is better.
If what you're looking for is like the attached jpeg, it was done with a 7-1/2" Cooke, and my dad was amused because a tripod leg was actually under the chair he was sitting on, and the lens was less than 3 feet from his face. To me, this is not a workable focal length for routine head and shoulders portraiture. Pardon the artifacts, it's type55 and was framed when I scanned it.
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Oh, and you did not say what size lens boards you have, but assuming they're 4" or so and your format is 4x5, here are some of the likely candidates for a good head shot portraiture lens.
240mm f:5.6 Apo Sironar S (Jock Sturges uses one on 8x10 IIRC, but not usually for head shots)
10" or 12" f:6.3 Commercial Ektar (Karsh used a 14" CE on 8x10)
240mm f:4.5 Tessar or Heliar. This is the largest f:4.5 lens you're likely to get on a small board, and it will take some custom work to do it.
9-1/2" (240mm) or 12" f:6.8 Dagor
250mm Fujinon Soft Focus
250mm Imagon in Copal or Compur #3
When focused to the identical close distances for a head portrait, the angle of view for a large format camera narrows much more than a 35mm camera, thus making the common 'format ratio' formula less reliable. The equation is perfect at infinity, though.
This calculator includes a magnification factor: http://eosdoc.com/jlcalc/
Here's another way to think about this, if you want to sort out what is practical with the equipment you have.
A really tight 4x5" headshot has a magnification ratio of about 1:3 (image size:object size).
Many 4x5" cameras have a double extension bellows, or 12" (about 300mm), some like Linhof have a triple extension bellows around 16-17" (around 425mm), and on top of that it is possible to add more extension on some monorails with additional standards or to use a "top-hat" extension lensboard, or to add extension tracks, or just to use a larger format camera with a longer bellows and 4x5" back.
On a camera with a minimum double extension bellows, you need 280mm extension with a 210mm lens, so you've got a little space to even get a little closer than 1:3, and subject distance will be about 2 feet.
240mm non-tele lenses tend to be designed for 8x10" and are in large shutters and may not fit on a 4x5" camera, but if it does, then it needs 320mm of bellows, and you only gain a few inches of subject distance over a 210mm. A 240mm telephoto design will work with a 4x5" camera and double extension bellows, if you have a 240mm tele you like.
300mm lenses can be more compact and a non-tele design will require 400mm of bellows at that magnification--pretty stretched out on a Linhof or other triple extension camera, but do-able, and subject distance goes up to about 3 feet.
360mm opens up the possibility of a few telephotos that can work on 4x5" with not so much bellows--not a common choice, but a Tele-Xenar of that focal length will give you 1:3 magnification at about 300mm extension, and subject distance of about 3-1/2 feet.
500mm non-tele will require about 670mm of bellows--most easily done by putting a 4x5" back on an 8x10" camera. A 500mm Tele-Xenar needs about 420mm of bellows, so it should just work on a triple-extension 4x5" camera, and subject distance will be about 5 feet. 500mm telephoto lenses are available for 4x5", but aren't that common.
Best to work with studio strobes for this amount of magnification.
Last edited by David A. Goldfarb; 08-25-2011 at 08:26 PM. Click to view previous post history.
This would work OK when the aspect ratio of the formats are similar...645 vs. 4x5 vs. 8x10. It works horribly when you take the overly long 3:2 aspect ratio of 135 format and try to equate it to a 5:4 ratio format, which is the logic behind using the short dimension of the frame (which is the narrow dimension used in single portraits...nobody ever prints a 16x24 or 8x12 for a portrait...they print 16x20 and 8x10 for the frames that go on walls and desks. Simply by altering D to not be 'diagonal' but 'short dimension', the same formula still works.
Originally Posted by Ian C