think tank forum

how does one go about calculating the neutral focal length for a given film or sensor size?

I'm not sure what you mean by this term exactly.. hyperfocal distance?

if that is the case..

http://www.dofmaster.com/hyperfocal.html

i think it's more like this:
http://en.wikipedia.org/wiki/Crop_factor

and:
http://en.wikipedia.org/wiki/Normal_lens

well all three are good to know I suppose :D

woah i don't know how i did that -- think that you were someone else.. probably the avatar switch.

anyway i still don't know what 'neutral focal length' means either exactly.

i seriously need to stay off the internet today. BYE

haha

so what did you mean by neutral focal length?

"normal lens"

i don't like that term, because i could have a zoom lens with which one particular focal length is "normal."

so it's not the lens that is normal--it's the focal length. which is why i call it "neutral focal length" or "normal focal length."

BRING IT ON PHOTO KIDS

I hadn't heard either term before, but I suppose it makes sense :o

Actually i think 'normal lens' is a colloquial term for fixed (focal length) lenses. Neutral focal length makes me think that there is an ultimate focal length for any given lens, and that you just need to determine the perfect length.

If you're wanting to determine what is a digital-cam lens focal length equivalent, considering the sensor size, to a film lens with normal film size i think the answer is in crop factor calculations!

There is a problem with this if you get a lens that is built for digital sensors though. They may already give you the focal length equivalent to film!

dp> Neutral focal length makes me think that there is an ultimate focal length for any given lens, and that you just need to determine the perfect length.

not at all! but there is an "ultimate focal length" for a given film size or sensor size.

if i say that the neutral focal length for a nikon d90 is 28mm, i'm not saying that any given lens will suit it. the lens must be able to produce a focal length of 28mm.

dp> i think the answer is in crop factor calculations!

i don't think so. it seems that image diagonal determines the normal lens focal length. so the sensor size determines the normal lens focal length. the nikon d90 uses a dx format sensor, which has a image diagonal of 28.4mm. so the normal lens focal length is 28mm.

So neutral focal length is the minimum diagonal that does not produce vignetting on the sensor?

i'd assume it would be longer than that.

can you please explain what you're trying to get at?

No, I'm trying to figure out what you mean. I'm not explaining anything.

there is an "ultimate focal length" for a given film size or sensor size.

WHAT? So you maybe are talking about hyperfocal focusing.

Most of my posts were regarding lens to lens equivalents from sensor to film. I don't know what you mean by any of this now.

From what I've read, 'normal' refers to the FoV of human eye. 50mm is considered 'normal' on full-frame camera.

http://flickr.com/groups/d40slr/discuss/72157603326462020/