Infinity

[Tempura]

Sorry for the stupid question. What does infinity actually mean?

[farrukh]

It means: something without limits :-)

May be you are talking about infinity mark on lens, Here it means when you want to shoot a distant subject like Landscapes, but you cant focus it due to a problem, then you can set the focus manually to infinity and shoot.

[Tempura]

Sorry, I still don't understand. Does it refer to a focusing distance beyond a particular point?

[Bob_A]

Yes, if the camera will focus from a certain point to infinity, it means it will focus from that point to an infinite distance past it.

[Tempura]

No, I mean the point at infinity mark. What is the focusing distance when the lens reach that mark?

[René Damkot]

Very, very far away. I mean, like really mind boggling far ;)

[Choderboy]

Very, very far away. I mean, like really mind boggling far ;)

..like...infinity :)

[Choderboy]

I think what you need to know is at what distance for a particular lens should you use infinity. Shooting the moon - now there's an obvious case for using infinty.

[Tempura]

I think what you need to know is at what distance for a particular lens should you use infinity. Shooting the moon - now there's an obvious case for using infinty.

Besides the moon, how FAR is very far away? Is something several miles away "very far"?

[Choderboy]

Besides the moon, how FAR is very far away? Is something several miles away "very far"?

Definitely.
Someone may be able to provide an accurate answer , but for example , when using my 200 prime I use infinity when shooting objects less than 1 kilometre away.

[DavidEB]

when you can use the infinity mark depends on the depth-of-field of your lens at the aperature you're shooting. If you're using an ultra-wide angle 10mm at f/16, you can set the lens to infinity focus, leave it there, and anything farther than your elbow will be in focus. If you're using a 400mm at f/2.8 and focus on an object 1/2 mile away, the distant mountains will be a blur.

[PaulB]

Definitely.
Someone may be able to provide an accurate answer , but for example , when using my 200 prime I use infinity when shooting objects less than 1 kilometre away.

How much less than 1 kilometer? 950 metres less?

In photographic terms infinity can be taken to mean the distance beyond which it is not possible to focus - although some lenses do focus 'past' the infinity mark to allow for thermal expansion/contraction of the lens barrel and optical components.

[Tempura]

when you can use the infinity mark depends on the depth-of-field of your lens at the aperature you're shooting. If you're using an ultra-wide angle 10mm at f/16, you can set the lens to infinity focus, leave it there, and anything farther than your elbow will be in focus. If you're using a 400mm at f/2.8 and focus on an object 1/2 mile away, the distant mountains will be a blur.

So what happens if you set the 400mm at f2.8 lens at infinity? Is there a way to find it out?

[PaulB]

Infinity as set by lens manufacturers will in fact be a finite distance and will be different depending upon the manufacturer and the lens focal length. To work out the exact depth of field you would need to find out the Infinity focus distance for the 400/2.8L and as far as I can see Canon does not publish this information.
Taking a tree at 800m (c. half mile) and mountains at effective infinity and the 400mm at f2.8 then at Infinity the mountains would be in focus and sharp but the tree would not as the DoF doesn't extend that far back.

[wazmunstr]

heres how it works... made a quick drawing for ya.

http://img.photobucket.com/albums/v142/wazmunstr/canon%20forum/untitled.jpg

every lens is different so the distance to that point will vary.

[Jon]

For all practical purposes, substitute your lens' focal length for f, the focal length + 0.05 for i, and your answer, O (in mm) will be the distance at which you can safely use infinity.
1/O=(1/f) - (1/i).

[Double Negative]

...and beyond! :D

Next topic: "Hyperfocal Distance and You"

[nwyman]

oh, God!


nancy (more confused than ever)

[Jon]

The longer the lens, the further away infinity is - how's that? But it isn't linear. It's not 28 m for a 28 mm lens and 400 m for a 400 mm lens. It's more like 14 m for a 28 and 8000 m for a 400 mm lens. But it doesn't matter. You have auto-focus on your camera, and you've got a screen that'll help you focus if the AF isn't working as you'd like. So don't worry about it.

[nwyman]

The longer the lens, the further away infinity is - how's that? But it isn't linear. It's not 28 m for a 28 mm lens and 400 m for a 400 mm lens. It's more like 14 m for a 28 and 8000 m for a 400 mm lens. But it doesn't matter. You have auto-focus on your camera, and you've got a screen that'll help you focus if the AF isn't working as you'd like. So don't worry about it.

Whew! To old for math at this point.


nancy

[Tempura]

Thanks everyone. So here are the conclusions (if I'm correct):

(1) "Infinity" (in photographic terms) really refers to a finite distance.

(2) Beyond that point, everything will be out of focus.

(3) The infinity distance varies among lenses (longer focal length produces longer infinity distance).


I really hate to have misconceptions about basic terms. Thanks for the clarifications provided here. By the way, using the formula shown by Jon, I found that the infinity distance for a wide angle lens to be very short (32 meters for a 40mm lens? Even shorter than the hyperfocal distance if aperture is like 1.4. I wonder if I've screwed up the calculation?)

[Jon]

1) Infinity is infinity - somewhere out beyond the stars. But your DoF is what makes it possible to use it at shorter distances.
2) 'beyond" implies that "further away" everything will be out of focus. If you focus at infinity, things closer in will be out of focus.
3) See #1 - Infinity's always way out there - but DoF for short f.l. lenses is greater than DoF for long lenses.

The 0.05 number came from using f/2.8; for f/1.4 it's about 1/2 that; for f/5.6 it's double.

[Tempura]

Jon, so what is the dof if a 40mm lens is set to infinity?

[Tempura]

I guess I can answer my own question - the dof wil be between the hyperfocal distance and inifinity, right?

[Jon]

I guess I can answer my own question - the dof wil be between the hyperfocal distance and inifinity, right?You got it.

[Bob_A]

This site may help you:

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

Lots of good information regarding the calculation of hyperfocal distance, etc if you're interested.

[FlashZebra]

heres how it works... made a quick drawing for ya.

http://img.photobucket.com/albums/v142/wazmunstr/canon%20forum/untitled.jpg

every lens is different so the distance to that point will vary.
This drawing make no sense at all.

If those are light rays in the diagram, then this definitely does not show infinity. At infinity light rays are parallel to each other and never intersect. In fact this is often used as a practical physical description of infinity.

For infinity focus, light rays would arrive at the lens parallel to each other. This never actually happens, but at very far distances (approaching infinity) the rays arrive at the lens in a manner that approach being parallel to each other.

Enjoy! Lon

[FlashZebra]

Sorry for the stupid question. What does infinity actually mean?
Just pick up a dictionary and look up the word infinity.

Or go here and check out the meaning.

http://dictionary.reference.com/search?q=infinity

The photographic meaning is consistent with this dictionary definition.

If this does not get the job done, well good luck.

Enjoy! Lon

[mbze430]

http://en.wikipedia.org/wiki/Infinity_focus

[storeman]

Simple answer....

For any given lens at any given aperture, infinity is the nearest distance the lens will focus upon when set at infinity. everything from that point and beyond will be in focus.

[Jesper]

In fact, nobody knows if "infinitely far away" even exists, since nobody really knows if the universe is infinitely large (http://en.wikipedia.org/wiki/Universe#Size_of_the_universe_and_observable_unive rse)... :p :lol:

[pknight]

..like...infinity :)

"... and beyond!" (B. Lightyear)

EDIT: Sorry Double Negative, I did not see your post before posting this. You are very clever!

[Double Negative]

:-P