How far away is infinity? (optically speaking, of course)

[Bill Clark]

"I think you need to qualify that as the "visible universe" which is very far from being infinitely large unless you define infinity as being limited by visibility. i.e. you can't focus on anything which is invisible, which is that which isn't sending you light waves to focus. So as far as lenses go there is no such thing as infinity."


Good point.

However, visible to humans may have a different definition with another species. Years ago my wife & I were visiting our daughter, who was living in Chicago at the time, going to visit an exhibit and one area had butterflies and I learned that some use the UV spectrum to see. It was interesting how the male & female butterflies were quite easily identifiable under UV light!

In photography, sometimes I try my hand and use IR film to see what it sees!

Interesting discussion.

 

[Rob-F]

Can this be infinity?:

Infinitely small until there is nothing?

Is nothing (0) infinity?

Infinitely large, example the universe? Perhaps not a good example if it isn't infinitely large?

Photography is important to the discoveries and the discoveries are important to photography. There is an interesting book titled, "Leica M - Advanced Photo School," by Gunter Osterloh. Check it out if you get a chance to peruse a copy and look at all the mathemetics involved in lens design. Leica M lenses starts on page 99.

Did you hear about the astronomer who went to a party but only stayed for a short amount of time? S(he) didn't like the atmosphere! Ha!
At any rate, here is a spot to check out on infinity:

http://scidiv.bellevuecollege.edu/math/infinity.html

Thanks for strarting this thread!

Hi Bill, you are welcome! My calculus teacher said that infinity is the process of allowing a number to increase without bound. Zero is not infinity. It's zero. But a number can be allowed to decrease without bound, as well as increase without bound. This is referred to "as x approaches zero" (but never reaching zero.) So to a mathematician, it's a process, not a size.

I have two copies of Osterloh, one is an early edition, the other recent. Thanks for mentioning this book, it is a good one for Leica photographers, as well as others.

 

[Roger Hicks]

Roger, optical phenomena are anything but unquantifiable.

We aren't talking about optical phenomena. We're talking about "how far away from a camera/lens is far enough that it can be considered infinity?" (the OP's question).

So I stand by what I said.

Cheers,

R.

 

[.... _]

"I think you need to qualify that as the "visible universe" which is very far from being infinitely large unless you define infinity as being limited by visibility. i.e. you can't focus on anything which is invisible, which is that which isn't sending you light waves to focus. So as far as lenses go there is no such thing as infinity."


Good point.

However, visible to humans may have a different definition with another species. Years ago my wife & I were visiting our daughter, who was living in Chicago at the time, going to visit an exhibit and one area had butterflies and I learned that some use the UV spectrum to see. It was interesting how the male & female butterflies were quite easily identifiable under UV light!

In photography, sometimes I try my hand and use IR film to see what it sees!

Interesting discussion.

IR or visible to humans it's still limited to visible by any type of detector. Past that point and it becomes theoretical only. For example we can infer the prescence of a black hole but we can't actually see it since it doesn't send us anything to see. So for any detector the limit is the event horizon and the event horizon is never at infinity.

 

[.... _]

I have always considered lens infinity to be the point at which the light rays are as close to parallel that any closer makes no discernable difference in the final image output. How close that is is dependant on the variables as discussed in the zeiss document on DOF.
Tricky to nail it down but if you are testing a lens then pick something at least twice as far away as you think you need to which roughly speaking will be twice as far as your lens distance scale is telling you is infinity and you should be OK.

 

[Dralowid]

I wonder how can a rangefinder work at infinity?

Surely with a baseline of no more than a few inches there would be no angle of view between the two 'views' ie they would be parallel and the images would never match?

And yet they seem to when set up right.

Then I think of the rangefinders you could see on heavy warships of the late '30s (ie before radar ranging) and I think....hhhmmmm...long range gunnery using range finders and mechanical mathematical devices (avoiding the use of the word computer) must have been truly impressive.

But does that have anything to do with infinty??????

Michael

 

[ferider]

Depending how accurate your camera registration and rangefinder adjustment are, how sharp you want the outcome to be, how much resolution the lens has, how much you care and compensate for focus shift, etc.

Traditionally the rule of thumb for RFs was 1000 x focal length. With modern, sharper lenses, you might want to increase that to 4000 x focal length or similar and as suggested above.

Roland.

 

[Sparrow]

Anyway, there is very little worth photographing that far away

 

[sevo]

The focusing mechanism doesn't enter into it. I'm assuming that the lens is being focused perfectly. DOF does not enter into it.

As to aperture: the effect of a small aperture would be only to mask that difference, via DOF.

Something that does need to enter into it would be the size of the blur circle.

In absolute terms, photographic infinity is the lens-to-focal plane distance where rays entering the lens in perfect parallel coincide in one point on the focal plane. For any "practical value", we're talking of some sort of hyperfocal distance - but there, the above do matter.

 

[Rob-F]

An interesting, wide variety of associations to this topic! Everything from Butterflies to black holes! Infinite universe, parallel universes. Rangefinder calibration. Lenses that focus past infinity. 42. (That last should be in AU's, BTW, not meters.)

Traditionally the rule of thumb for RFs was 1000 x focal length. With modern, sharper lenses, you might want to increase that to 4000 x focal length or similar and as suggested above.
Roland.

This is along the lines of what I was looking for.

In absolute terms, photographic infinity is the lens-to-focal plane distance where rays entering the lens in perfect parallel coincide in one point on the focal plane. For any "practical value", we're talking of some sort of hyperfocal distance - but there, the above do matter.

This is true, of course. I'll have to concede that hyperfocal distance does have to be considered. Let's try it this way, though: I wonder how many focal lengths, for optimum results, the subject would need to be for a lens that is optimized for infinity, rather than at some compromise middle distance?

 

[fstops]

This is an interesting topic.

I don't know the answer to OP but in my case I focus at infinity if I don't want the foreground to be in sharp focus. I focus at hyperfocal distance of a particular f stop if I want focus to be sharp from foreground to infinity.

If this is an incorrect method then please let me know.

 

[.... _]

Just to throw a spanner into the works, the following has a formula for calculating rangefinder focussing accuracy. I'm not sure I understand it cos 'e' is a new one to me and I have no idea where it comes from.

http://r-d1.info/camera-use/rangefinder-accuracy/

Basically I think its saying you better not go too wide otherwise your focussing will be off. I guess you can calculate for your cameras base length.

 

[semilog]

this was carefully calculated before. answer was 42.

What was the question, again?

 

[.... _]

What was the question, again?

The point was that if you are focussing on infinity to check your rangefinder accuracy at infinity, then you better be sure you are not shooting wide open otherwise you may be fooled into thinking your rangefinder needs adjusting when it doesn't. Just sayin....

 

[mdarnton]

It depends on your purpose. For adjusting the focus of my 85/1.5 on an M4, two miles was far enough. By that I mean that if I used any closer distance, I couldn't close the two images at farther distances, but aligning at two miles, more distance didn't matter.

If you are relying on or asking about "depth of field". . . there really is no such thing--the specific distance you focus on will always be noticibly better focused than closer or beyond. "Depth of focus" really means "how low are your standards, and what will you tolerate?"

 

[sparrow6224]

Ansel Adams, as others, accepted the formula of 1000 x focal length as the photographic distance called infinity. We need to know this number because sometimes we need to focus at 1/3 of that distance for best depth of field. For a 28mm lens, 28m, for a 50mm, 50m, and for 100mm lens, 100m. It makes sense. My source for the Ansel Adams is the first of his great series of three books, The Camera, The Negative, The Print. He mentions it in discussing focal length and depth of field in The Camera.

 

[Rob-F]

Vince, that is some great information. I even have those books, and it never occurred to me to look there. That is just what I was looking for.

Thanks!

 

[sparrow6224]

Rob -- Good Ruskin quote. I like Ruskin. His reputation was ruined by his marriage -- a very strange and amusing story that if you're interested in him you should look up.

And glad to help.

 

[Roger Hicks]

Rob -- Good Ruskin quote. I like Ruskin. . . . .

Interesting. I really loathe the fellow. He had an exceptionally and unjustifiably high opinion of himself and was the most repulsive and arrogaat reactionary in most matters artistic: think of his reaction to Whistler's Nocturne in Black and Gold: The Falling Rocket.

Also, amusing though it is today, that quote is nothing like as witty in the context of his time. In that context, before widespread affluence, it was the vapourings of a nasty little bourgeois snob.

The story about the marriage has been queried, incidentally. I suspect it has been embroidered by those who dislike him as much as I do, but are/were less scrupulous about how they blacken people's names.

Cheers,

R.

 

[Sparrow]

... and he often gets accused of burning many of JWM Turners less salubrious work while working as the old man's executor ... which I like to think the little ****e was capable of