No, that's an old, misleading rule or guide since the distance changes as the lens focal length changes and as your distance from the subject changes. You might want to read the article from the main page by QT on focusing the view camera to understand this better but the general idea is to focus on the nearest object you want to appear sharp, then focus on the farthest, then set the lens halfway between the two positions.Originally Posted by gliderbee
Brian Ellis
Before you criticize someone, walk a mile in their shoes. That way when you do criticize them you'll be
a mile away and you'll have their shoes.
I wasn't. I did assume that when suggesting the use of a smaller format it would be understood that a shorter lens would be used and the photo would be made from the same camera position.
One man's Mede is another man's Persian.
As EVH says, although I didn't state it I made the assumption that the shooter 'would' use the same equivalent focal length on the smaller format. Lets say he was using a 150mm lens on a 4x5, I wouldn't expect him to use a 150mm on a 35mm but if he used a 50mm lens stopped down to 16 you'd have a sharper print than a 150mm lens on a 4x5 stopped down to the same F stop.
I believe it has something to do with the circle of confusion, although I understand the principal I get confused when I try to explain it :-).
the circle of confusion is you three standing around a.................
The best system I have found is a good loupe, a fine groundglass and a good darkcloth. With patience and practice, you will be able to asess DOF on the GG, rather than wait until you have wasted a piece of film.
One man's Mede is another man's Persian.
In my experience, when you set the standard, with which you are focusing, half-way, as measured along the rail of your camera, between the furthest, and the closest, points on which you focus, you will have actually focused about 1/3 of the way from the point of closest focus, as measured in the field, towards the point of furthest focus. This assumes no swings or tilts, upright camera, and a level terrain.
In other words, the half-way point against the camera rail is about equivalent to the 1/3-way point in the field.
Ah Rafal, I've not checked that 1/3 factor carefully but I wonder if that is a function of a non symmetrical lens. Or put another way a lens where the entrance pupil is different from the exit pupil, say with a retrofocus design. In that case the 1/3 distance would not be consistent from lens to lens. Anyone have any real data on this as a function of different lenses?
Nate Potter, Austin TX.
Vinny? a................. A what?
Nathan, that sounds like a wonderful bit of optical knowledge that I would like to learn about—I admit, I have not paid attention to the intricacies of my telephoto lens focusing as much as I should have, the rest are conventional.
EVH,
While I agree that checking DoF with a loupe is a good method, I've found the method I linked to ( http://www.largeformatphotography.info/fstop.html ), after using the formulae and figuring out your desired CoC to be more accurate. I know that I cannot even resolve detail on a 4x5 negative with a 10x loupe that I can see clearly in a 16x20 print. I would need a microscope. I submit that the view of the detail on the ground glass is even worse, even with a 10x loupe, and most don't use such powerful magnification for gg viewing.
Also, the method linked to allows me to find the largest aperture practical for the size of print I plan to make, thus allowing me to reduce diffraction degradation to a minimum. I find this very helpful. I certainly can't see the degradation due to diffraction on the ground glass until I stop down well past the real diffraction limit...
I think I've wasted more film by overestimating my DoF by viewing on the gg rather than by using this method. Chacun á son gout.
Best,
Doremus
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