"Infinite" focus

[tinhorn]

I've always been a bit (a lot) unclear about the infinity setting on the focus ring. Does it mean that everything in the field is in focus? Is this a poor man's deep focus? What is sacrificed by depending on this setting, if anything?

Thanks.

[toby_tools]

If you are filming a subject that is 20ft from your camera then you set your lens to 20ft. If your subject is say 45ft and your lens only goes to 30ft on the focus ring then you set it to infinity. Because anything past 20 ft to infinity will be in focus.
Hope that is what you were asking.
Toby

[tinhorn]

Thanks Toby.
I know that it's useful beyond the last specified distance on the ring, but if a subject walks into view at 6 ft., will Infinity keep that in focus as well? Or do you have to rack down to 6 ft., thereby losing focus on the more distant background?

[toby_tools]

Yes you have to rack down to 6'.

I think your talking about "DEPTH OF FIELD"
If your actor is a 6' from the camera but you want the background to be in focus you need to use a a small aperture like f16 or f32.
Super 8 has a very deep DOF I usually like to shoot at a large opening like f 2 or f4, because I like a narrow DOF when shooting medium close up of my actors. That way my actor is in focus and the background is blurred making my actor the center of attention.
Search the INTERNET for DEPTH OF FIELD there are a ton of sites that go into detail about it. Also 35mm SLR photography is a good place to start.
You can take the film to a 1hour lab to see your results. Just use a fully manual camera so you can learn how it all works, you can find them on Ebay for less than $50.00
Toby

[themagickite]

if you use a mac, there is a great depth of field calculator widget that has a super8 setting. very useful

[mattias]

infinity means that all light rays coming in parallel through the lens will be in focus. how far away an object has to be in order for the light to be close enough to parallel to count as parallell (it never quite is of course) depends on the focal length, aperture and circle of confusion.

the distance you need to set the lens to in order to get as much dof as possible is called the hyperfocal distance, on which the dof extends to infinity and the near limit depends on the factors i mentioned.

in super 8 you very rarely need to set the lens to infinity, since the focal lengths are so short that the hyperfocal distance is always within measurable distance. for example even if you're on a 50mm at f/2.8 the hyperfocal distance is only 60 meters which puts everything from 30m to infinity in focus. hope this helps.

/matt

[David M. Leugers]

Another way to think of infinity focus is that everything from as far away as possible to a certain point closer to the camera will be in focus. The close factor is determined by focal length of the lens and the F stop the lens is set to. Wider lenses and higher F stops result in greater depth of field. The Hyperfocal setting is very handy. By being aware how close one came come to the subject and still remain in focus, for a certain lens and F stop, you can film away being assured what you shoot will have perfect focus.


David M. Leugers

[mattias]

Another way to think of infinity focus is that everything from as far away as possible to a certain point closer to the camera will be in focus.

that's dangerous though, if put into practice. much better to focus on the closer point and let dof extend to infinity then. in my opinion at least. the only times i ever use infinity is if i'm shooting distant landscapes and have foreground that i want to throw out of focus as much as possible. another reason to set it to say 100 meters rather than inf is that if your lens isn't collimated properly you will still get infinity focus while at inf you might get everything out of focus.

/matt