Also DOF is the same of lenses of equivalent focal length. So a 90mm lens on 35mm, which is a slightly long lens, has the equivalent DOF at a given aperture as a 90mm lens on 4x5 (which is a wide angle). On 4x5, the 90mm will have a lot more DOF at a given aperture than a longer lens, however it will have a lot less than the equivalent field of view lens on a 35mm camera (a 28mm lens on 35mm will have a lot more in focus at a given aperture than a 90mm lens will have on 4x5).
Image circle is the size of the useful image the lens will project and is independent of focal length. Angle of view is a function of image circle and focal length.Originally Posted by Oren Grad
The "looks like 50mm on 35" is a sometimes useful comparison to use with non-photograper types, but saying a 50mm becomes a 75mm when used on a smaller sensor is just plain wrong. It's a 50mm, always and for ever. The format size it what changes, similar, as Brian pointed out, to cropping.
One man's Mede is another man's Persian.
Your observation is incorrect. The focal length does not and can not change. This is very important to know, if you wish to be a competent photographer.
One man's Mede is another man's Persian.
Although it's common practice, I think it's a mistake to think of things in terms of 35mm camera lenses. Better to understand what a normal lens is for each format you use and work it out from there.
Steve.
Not sure what you mean by that. Within a given design type, image circle indeed scales with focal length. OTOH, starting from a blank piece of paper, for a given focal length a lens designer can choose from a variety of optical formulas to achieve a very wide range of possible image circles.
Anyway, I'm not inclined to haul out the wet noodle over the "equivalent focal length" usage unless the person using it stretches the analogy too far and starts to draw incorrect inferences from it. There's a glimmer of useful insight there; starting as beginners we find our way to a more complete understanding through many different paths.
A 6 1/4" WA Velostigmat has about the same image circle as a 9 1/2" Dagor and a 16 1/2" Artar. Independent of focal length. A 350mm image circle will give slight movements on 8x10 regardless of the focal length or design of the lens wich projects it, be it 160mm wide angle or a 19" process lens. Angle of view expressed in degrees is a function of lens design, image circle expressed as diameter of a circle is independent of lens design and focal length.
And, if you read the thread, you will see that the OP is indeed drawing incorrect inferences from "equivalent focal length".
One man's Mede is another man's Persian.
Okay, let me just restate my point, since I seems to have offended the sensibilities of some here with my crude and uneducated vocabulary in reference to the focal length of a lens.
I noticed that the smaller the piece of film I use, the smaller the picture I get.
Cletus, we are trying to steer you in the correct direction. This is how things go here. We argue amongst ourselves all the time here. There are many incredibly highly skilled folks - in more than photography- here, and this focal length issue has been dealt with more than once.
One man's Mede is another man's Persian.
By jove... now you've got it!
I restrained myself.......By jove... now you've got it!
One man's Mede is another man's Persian.
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