perspective vs format

[KevinUK]

Hi Everyone,

I'm thinking of getting into medium format (though this question is equally as relevent for using '35mm' lenses with smaller digital sensors) and have a question about perspective (i.e. NOT field of view):

I fully understand how a longer focal-length lens creates the same angle of view on a larger format film as a shorter focal length does on a smaller one. However, is the 'forshortening' effect of longer lenses independent of the film/sensor format as I believe, or does this also somehow change with the format?

Looking at it another way, if I go up in format and compensate for field of view by choosing a longer lens, will I change the aparent perspective in so doing?

Thanks
Kevin

 

[ksmattfish]

There are many sites that deal with this topic is great detail, but simplified, as I understand it...

If you shoot 3 images from the same spot, each with a different camera (4x5, MF, and 35mm), but the same focal length lens, the smaller formats will be like a crop from the center of the image from the larger formats. There will be no change in apparent perspective.

Here are some quotes from Ansel Adams' "The Camera"

"...all lenses of the same focal length give images of the same size for a given subject and subject distance. If a 4-inch lens produces an image one inch high of a certain subject, the image size will remain one inch regarless of whether the lens is on a 35mm camera or a 4x5 camera. However, on the 35mm camera, the one inch image will fill the frame..., while it will occupy only about one quarter the height of the 4x5 film."

"True perspective depends only upon the camera-to-subject distance."

 

[KevinUK]

Good point! I guess what you're saying means that as perspective stays the same for a given lens, regardless of format, then logically the forshortening effect of a longer lens will still be present even if its used to create a more wide angle of view on a bigger format. I think the fact that I was looking at it the other way around may have confused things, I never made the logical jump!

Thats interesting; I rather like the exaggerated perspective I get from short lenses on my 35mm SLR, but from this it would seem that achieving the same field of view on a larger format (i.e. by using a longer lens) it would result in more normal perspective. Not necesarily 'worse', just different.

Seems the concept of '35mm equivalent lenses' is used for field of view only. I understand theres a similar change in achievable depth of field, again associated with the differing lens lengths needed for the same FOV on different formats.

Thanks, very helpful indeed!
Kevin

 

[markc]

Here's a good article on what happens.

 

[KevinUK]

Looks like a very good article - thanks!

Its amazing that after all the photography magazines I've read and subscribed to over the years this has almost never been touched on, and yet there it is - at a high quality - on the web if you know where to look (or in my case if more knowledgeable forum people tell you!).

Thanks for your help, very useful,
cheers,
Kevin