Knowing that LF have equivalents in 35mm for focal length, eg. 120mm in LF (4x5) = 36mm in 35mm. If I'm using a 36mm lens to take the same shot as I would using the 120mm, is there any change in the f stop from the LF lens to the 36mm lens to get the equivalent light to the film. Or is everything relative with the lens and film sizes and the same amount of light will be transmitted by both lenses using the same f stops.
Same f stop at same shutter speed will be the same exposure assuming both shutters have the same timings (not too likely with LF shutters, I'm afraid,) but should be close enough for government work as the saying goes!
The computation (equation) to determine the f/stop of the lens includes the focal length (focal length divided by the diameter of aperature).
So f/16 at 1/125 of a second is the exact same exposure no matter what the focal length or format of the camera you are using. Assuming everything else is constant (light, film, bellows extention, etc)..
"Landscapes exist in the material world yet soar in the realms of the spirit..." Tsung Ping, 5th Century China
Beauty, thanks Vaughn that is what I was after.Originally Posted by Vaughn
HOWEVER, the larger the format, the less DoF there is a each f-stop. I.E., your f8 on a 35mm lens will give you the equivalent of ~f4 on 4x5. DoF is determines by 1) aperture 2) magnification.
Kent in SD
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Notte e di vogliam passar!
@Kent
Wouldn't it be the other way around? ie wouldn't the 4 x 5 (4 x 6 really if you want to be more exact) at f 8 have the DOF of the 35mm at f 4? Bigger film, less DOF. Although this would only be true if you printed the 4 x 5 image larger than the 35mm image. If you printed both equivalently exposed negatives at, say, 8 x 10, then the final enlargement in the print would be the same so apparent DOF in the two prints would be the same.
At least I think so. My wife says I'm wrong about almost everything, so why would this be an exception? Cheers.
When the final images are the same size, the DOF is the same when the aperture appears to be the same diameter as seen through the front of the lens, regardless of the f/number, focal length, or format. It's really that simple, although the basic math to reach that conclusion is perhaps more than many of us want to wrestle with. However, working out the relationships between focal length, aperture, f/number, exposure, and close-up photography may bring one closer to an intuitive understanding of these sometimes arcane matters. It certainly helped me decades ago when our tools were pencil, paper, and perhaps a slide rule.
For lenses of the same angle of view on different formats, the aperture size in millimeters correlates pretty well with DOF if subject distances are relatively far away.
I believe apparent DOF between 35mm and 4x5 is 4 stops not 2. e.g. f/16 on 4x5 mm has similiar DOF to f/4 on 35mm
Yes. We think of larger formats having less depth of field, but it's really longer lenses, which at the same f-number have larger entrance pupils, that have less depth of field. So, a 35mm lens (as might be used with 35mm format) at f/2 has an entrance pupil of 17mm, and for a 135mm lens (as might be used to make approximately the same photo on 4x5), a 17mm entrance pupil would be f/8. Thus, f/2 gives approximately the same depth of field on a 35mm lens as f/8 does on a 135mm lens, when used to make the same photo printed to the same size. But, to make the same photo with those two lenses, one needs different formats.
Rick "that math is actually simple enough for day-to-day use" Denney
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