"Where" is infinity?

[djotaku]

I did a search on "infinity" and couldn't find what I was looking for. In other words, on my better lenses I have the focal distance meter. The furthest part is labeled infinity. Obviously, infinity can't be in in focus.

My main interest is this - let's say I'm doing some candid street photography. Or maybe shots of very active kids. I want to prefocus and then just shoot. So if I put it at infinity, how far do they have to be to be in focus? And how far can they be and still be in focus?

Thanks!

[sybren]

If you want to maximize your depth of field, read up on hyperfocal distance focussing. It'll also explain about your question regarding infinity.

[jprime84]

The way I understand it is infinity focus is focusing on an object that is - for all intents and purposes, an infinite distance away. Geometrically, this corresponds to the focal point for parallel rays of light.

If you think about the light traveling from everything in your cameras field of view to the sensor, objects that are closer to you have a wide angle that light has to be focused onto a point to be "in focus." Objects that are extremely far away basically have all of the rays of light moving parallel towards your camera by the time they get to you.

[LoveDSLR]

Originally Posted by djotaku

I did a search on "infinity" and couldn't find what I was looking for. In other words, on my better lenses I have the focal distance meter. The furthest part is labeled infinity. Obviously, infinity can't be in in focus.

How about focusing beyond infinity?
I found a very good thread about this. Check it out at http://www.luminous-landscape.com/fo...php/t9696.html.

My main interest is this - let's say I'm doing some candid street photography. Or maybe shots of very active kids. I want to prefocus and then just shoot. So if I put it at infinity, how far do they have to be to be in focus? And how far can they be and still be in focus?

1) Prefocus on something else at equal distance and pan across with the kids; or else try to step in sync with the kids to maintain equal distance
2) Apply hyperfocal focusing assists by DOF preview

[kencaleno]

infinity strats around 30 feet and extends to as far as you can see-If you want everthing to come out acceptably sharp from 2 feet six to infinity, using your 18-55 lens at 18mm,focus on a point 5 feet from you. Here are hyperfocus charts for 18-55 and 70-300 lenses. (From distance shown,half of that distance to infinity will be acceptably sharp) Concerning street photography,what we used to do was either use a 35mm or 50mm lens focused at 5 metres(15 feet) on a rangefinder 35mm camera; exposure was pre-set using the "Sunny-16" rule.

regards, Ken

[candleman]

i've counted to infinity a couple of times..
its one of those things where if you've done it once.. its gets a bit boring the second time around. kindof like watching the sixth-sense when you know the ending.

[OsmosisStudios]

Originally Posted by kencaleno

infinity strats around 30 feet and extends to as far as you can see

*Varies by lens. Generalization.

[HoosierGal]

Originally Posted by candleman

i've counted to infinity a couple of times..
its one of those things where if you've done it once.. its gets a bit boring the second time around. kindof like watching the sixth-sense when you know the ending.

Ah, but have you counted backwards from infinity?

[mfreg]

What I don't get ( or didn't ) is this........My eyes aren't so good any more, so when taking some pictures of the moon a few months ago, with my 100-300mm lens, I just set it to infinity and thought "I'm good to go".....the moon has got to be in the infinity range, especially if I use a small aperture right ?.....when I downloaded my photos to my computer I found NONE of them in focus.........What I read later, was that due to extreme cold or heat ( it was very cold ) your lens will contract or expand and throw your focus off. I never thought too much about the fact that I can go past infinty with my focus ring, I guess that is to account for that variance. Bottom line..I need new glasses ..

Hopefully this is correct and doesn't confue anyone.

regards
mike

[fletch]

Originally Posted by candleman

i've counted to infinity a couple of times..
its one of those things where if you've done it once.. its gets a bit boring the second time around. kindof like watching the sixth-sense when you know the ending.

But which infinty. There is more than one!

Just ask yourself, "How many whole numbers are there in total? 1,2,3,4,5,6... 1000,1001,1002... Well there is an infinte number of whole numbers right?"

"OK, how many decimals are there between 1 and 2? 1.1, 1.2, 1.3... 1.3111, 1.3112...Well there are an infinte amount again?"

"So hang on a minite within the total number of whole numbers there are an infinite number of infinite numbers?"

*Goes to find an Asprin*