Where is Infinity?

[Dan Jolicoeur]

Wouldn't infinity be as far as the eye can see on that particular day, and then beyond that? If it is a clear day it may be unlimited or about 50-70 miles. Or on a hazy day it could be 500'.

[Struan Gray]

How do I get Aleph on this keyboard?

The really long definitions of infinity are derived from the optical engineering meaning of "diffraction limited". Simply, all other forms of blur should be one tenth of the blur from diffraction. This increases my second formula by a factor of 10.

Note that simply multiplying the focal length by a number, and ignoring the aperture setting, is doomed to be wrong. Good enough for goverment work, but wrong enough to bite you in the backside when you really need it.

My favourite definition came from Pete Andrews in a photo.net discussion:

Infinity is quite a lot further away than most people think. It's even further than the horizon, which is also quite far away. Try pacing out the distance to the horizon, and then multiply that distance by several.

[Doremus Scudder]

I never focus on infinity. It seems I am always focusing on something a bit closer, like the horizon or a distant tree... Following this logic, it would seem that, even for the most distant objects we photograph, the point of focus should be slightly less than infinity (in an ideal world with no optical aberrations, of course).

Seriously though, unless we are "guess focusing" or using stops that are set for a certain distance, why do we need to worry about infinity? I just make sure that what I want to be sharp is as sharp as I can get it.

Best,

[Louie Powell]

New Jersey

[Pete Caluori]

Thanks for catching that Paulr, I did indeed mean not conservative enough.

Regards, Pete

[Walt Calahan]

The best I can remember from intro to photography way back in 1975, the answer to the exam question was "the moon" is considered "optical" infinity.

[mark anderson]

after a long absence from computer forums it is good to see that intelegent conversation still is still out there, how far out there is another question ;-).

if the moon is to be considered infinity, why then must i refocuse when i turn my telescope to mars.

i think the true answer to the question was found many years ago on a back road in maine

"ya cant get thare from hair"

[John_4185]

Seriously though, unless we are "guess focusing" or using stops that are set for a certain distance, why do we need to worry about infinity?

I'm messing with some aerial cameras that have fixed focus.

[Walt Calahan]

"optical infinity" for camera lenses and camera rangefinders, not telescopes.

Since I didn't think I was writing for an astronomy forum, I left off that qualitying clause.

Grin

[Graeme Hird]

Infinity is the point where two parallel threads meet.

I bet if you visit Photo.net's LF forum you would find a parallel thread there - when they converge we will have reached infinity ...