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Focus at 2 times infinity

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Started 3 years ago by jonnyapple
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jonnyapple

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Someone posted some stuff by Hiroshi Sugimoto a while back. He does some great work.

On spraynpray's sharpness thread I was reminded of one of his books that I once saw. It had architecture photography where he had intentionally put his lens's focus at twice the distance it would be for infinity (whatever that means! Someone please explain). Has anyone ever done this? I honestly just laughed when I saw it—does that make me uncultured?

He did it on a view camera (8x10, I think), but does anyone know if there is a way to do this with an SLR? It seems like maybe you could put on a 50mm macro extension tube on a 50mm lens focused at infinity. Is that the kind of thing he did?

edit: I found a link to his website with some of the stuff. http://www.sugimotohiroshi.com/architecture.html

Posted 3 years ago #
mb

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I doubt you could do that on SLR camera but putting a lens twice the infinity focus can be done on a large format camera by bringing your lens twice closer to the focus plane.

Posted 3 years ago #
NSXType-R

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I'm not exactly sure either, but apparently that's a feature in the new 24mm 1.4.

Check out Moose Peterson's review.

http://moosepeterson.com/blog/?p=14276

It focuses past infinity.

I have no idea what you're supposed to use that for.

Posted 3 years ago #
ChrisLange

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many autofocus lenses, especially ones with ED lenses focus past infinity because ED glass changes focal length slightly depending on temperature.

Posted 3 years ago #
heartyfisher

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My theory is that it needs to go past infinity for the autofocus to know its passed and then bring it back without it hitting a mechanical barrier at infinity..

Posted 3 years ago #
ShadeofBlue

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heartyfisher said:
My theory is that it needs to go past infinity for the autofocus to know its passed and then bring it back without it hitting a mechanical barrier at infinity..

Actually, that's not how autofocus works, at least not the phase-detect autofocus used in DSLRs. Basically, the camera can detect how out of focus the subject is and just move the focusing elements the correct amount. This is why issues like front and back focus can exist, which wouldn't occur if focusing worked the way you describe.

It is entirely because of the ED elements as far as I know.

Posted 3 years ago #
heartyfisher

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ShadeofBlue said:
Actually, that's not how autofocus works, at least not the phase-detect autofocus used in DSLRs. Basically, the camera can detect how out of focus the subject is and just move the focusing elements the correct amount. This is why issues like front and back focus can exist, which wouldn't occur if focusing worked the way you describe.

It is entirely because of the ED elements as far as I know.

Makes sense.. so in that case, if you have a lens that is front/back focussing, the live view contrast detection focusing will be more accurate? albeit a bit slower?

Posted 3 years ago #
Erik S

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heartyfisher said:
Makes sense.. so in that case, if you have a lens that is front/back focussing, the live view contrast detection focusing will be more accurate? albeit a bit slower?

Yes Live view will be more accurate(atleast if there is a problem). Using liveview to check focus is a good way to go if you are adjusting a back/front focused lens.

Posted 3 years ago #
clillja

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Seems like (and looks like, from his examples) he's simply doubling the back focus distance on his lens. Let's say he's using a typical 8x10 lens 240mm or so. At infinity, the rear nodal point of the lens lens is approximately 240mm from the film (or sensor). As the lens moves farther away, the focus point gets closer, so if he's moving the lens to 480mm away from the film he's focused considerably closer, for an object 1/4 mile away it's a blurry image, but still (according to him) an image where you can make out the outline and strong lines of good architecture. Or perhaps it's just a gimmick and he's full of it.

I think twice the focal length back focus gives approximately a 1:1 reproduction ratio with a focus distance of 4x focal length. He's focused at 960mm - Wayyyy out of focus for a near infinity object - perhaps slightly less so at f64? (Again, typical for 8x10 photography.)

See here for the math: http://www.jeffree.co.uk/pages/macro-lens-calcs.html

And they have some nerve calling it "live view" when it really about 1/25 sec behind the times. Lets call the optical VF the "Live View" and other thing "Delayed View". Or "blurry view." Or "grainy veiw." Or "super slow AF view." Oh yeah, the marketing dept. wouldn't go for it...

Posted 3 years ago #
mb

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Actually it looks other way around or close objects would be in focus.
For 240mm lens to focus to infinity the lens has to be at 240mm from the film as you mentioned. But if you move the lens closer (it is possible on large format because you are using bellows) to half that distance (120mm) you will be focusing at twice the infinity, as I mentioned earlier ;), and everything would be out of focus, closer subjects more and more distant ones less and that is the case in those photographs as far as I can tell.

Posted 3 years ago #

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Focus at 2 times infinity

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