View Full Version : Distance between near / far focus points

Mark McCarvill
15-May-2005, 20:10
I'd be interested in hearing how close people get their near / far focus points – before they stop down the lens. As a LF beginner focusing my 90mm SA at F8, the best I can do is get near / far to within about 2-3mm before splitting the difference and stopping down, usually to F22.

But in Jim Stone’s view camera book, he seems to suggest one can get near / far in focus simultaneously, before stopping down. Is this doable, with practice?


Juergen Sattler
15-May-2005, 21:06
Hi Mark, read this: http://largeformatphotography.info/how-to-focus.html. It explains very well how to focus the view camera- you cna basically pick any two points on your GG and get them into sharp focus - be the objects 2 feet or 200 yards apart. It's an iterative process by using tilt and focus.

Leonard Evens
16-May-2005, 06:45
I asssume you are talking about what happens when you tilt. Of course, with no tilt or swing, the distance between the near and far points on the rail doesn't change.

When focusing on one exact subject plane, I can manage to reduce the focus spread between my near and far points essentially to zero. There is always going to be a slight focusing error, which is inevitable, and depends on the aperture at which you focus and the the degree of magnification of your loupe. I normally just use my +5 diopter glasses, specially made for the purpose, and that lets me focus to within a mm. If I use a loupe I can get it down to less than half a mm. (I have a scale on my focusing knob which enables me to place the standard with an accuracy of something like 0.2 mm.)

Most subjects, however, are not restricted to a single plane. So I then pick a "high" and "low" point above and below the exact plane and measure the shift on the rail between them. I use that to determine how far to stop down.

As Juergen already noted, this is all described in detail on the large format web page.

Alan Davenport
16-May-2005, 11:07
IF your entire subject lies in a single plane, and IF you camera allows the needed movements, and IF your lens has sufficient coverage, then you should be able to get your entire subject in perfect focus before stopping down.

In the real world, few subjects lie in one plane. When the lens is tilted, for example, you might be able to perfectly focus the near foreground and the base of a far tree, but the top of the tree will not be focused. It is impossible to perfectly focus a non-planar subject onto a 2D piece of film, so there will almost always be a near/far focus difference with real-world subjects.

When using the near-far/split the diff/stop down technique, "near" and "far" refer to movement on the camera rail to focus all points in the 3D subject space, onto the 2D film plane. When the lens axis is not normal to the film plane, the "near" and "far" of focus may or may not be nearer and farther from the camera.

Mark McCarvill
16-May-2005, 14:18
“When the lens is tilted, for example, you might be able to perfectly focus the near foreground and the base of a far tree, but the top of the tree will not be focused.”

Thanks, Alan. This is what I have found in practice (with pretty much the landscape setup you describe) and I was wondering if I was doing something wrong because I could not get all of those 3D points in focus at once because some of the literature suggests one can do so.

Juergen and Leonard – thank you for the tips and references. I had read that how-to article and a number of others. Helpful stuff.