"focus to infinity" question

[jowensphoto]

If you have a lens with no infinity sign on it, how do you focus it to infinity?

 

[KmH]

By looking in the camera viewfinder, or using the camera's Live View mode as you focus.

 

[john5189]

Even with no focusing prisim you'll be surprised how close to focus you can get by concentrating on what you see in the viewfinder and manually focusing.

BTW I dont think any photons of light have actually reached Earth yet from infinity ro beyond.

 

[KmH]

Infinity is a notional concept that is more a math construct than a real entity.

For photography here on earth that isn't done by pointing the camera up at the sky, infinity, in photographic terms, is effectively the local horizon.

 

[KirkS]

BTW I dont think any photons of light have actually reached Earth yet from infinity ro beyond.

Then explain Buzz Lightyear...?!?!

To the OP, 'infinity' is at the end of the focus ring in the opposite direction of the closest focusing end.

 

[Hobbytog]

Turn the focus ring to the longest focal distance, select f22, put the camera on a tripod, click and that will probably be the longest dof you'll get. To understand more about infinity focusing 'Google' "Hyperfocal"

 

[christop]

Turn the focus ring to the longest focal distance, select f22, put the camera on a tripod, click and that will probably be the longest dof you'll get. To understand more about infinity focusing 'Google' "Hyperfocal"

For hyperfocusing you want to set the lens to "half-way" between the hyperfocal distance and infinity, which will be much closer to you than infinity. The hyperfocal distance on a 28mm lens is about 6 feet at f/8, and about 2.3 feet at f/22. It's easy to see what the hyperfocal distance is if your lens has a distance and depth-of-field scale (as my manual 28mm lens does) but pretty difficult without them.

(For outdoor "street" style of photos I normally keep my lens focused at about 11 feet and set to f/8, as 11 feet is half-way between 6 feet and infinity, so everything between 6 feet and infinity will be acceptably sharp. This is so I can aim and shoot and not have to think about focusing.)

But the OP is asking how to focus at infinity, not at the hyperfocal distance. Many (most?) auto-focus lenses can focus "past" infinity for some reason or another (probably so the AF motor can run past infinity without a hard stop), so this makes it difficult too. If you have to focus at infinity on an AF lens, try focusing on a distant object like clouds or the moon. That's about all you can do.