Focusing at the Correct Distance to Maximize the Depth of Field

[Salmo22]

WOW - What an amazing response. Lots to digest; however, I'm patient and committed to learning the proper technique. With study and practice, I'll get this.

Many thanks to all who offered comments and suggestions.

Regards;

Jeff

[Jim Jones]

As I recall from calculations I made long ago, a scale like that which Doremus posted is a universal scale for any lens but for just one particular image size. For critical work with 35mm cameras, the once prevalent DOF scales were suitable for fairly small prints, perhaps up to 8x10. A similar scale giving the DOF for a range of apertures can be added to the metric scale Doremus suggests. It will be tiny on such a linear scale.. Incorporating a magnifier helps. Consider that optimum DOF varies widely, dependent on the medium, the subject, the observer, the image size, and the viewing distance. It should be art, not science.

[aduncanson]

Great answer Doremus. It reminded me that Sinar cameras have a mechanical calculator built into the rear standard to do this for you. I was expecting to find a constant ratio between focus spread and optimal f-stop indicating a constant circle of confusion, but that is not what I found. In creating that table, the authors considered the effects of diffraction limiting resolution as you stop down and actually point out that as you stop down, you must limit your enlargement to maintain a sharp print. Note that even at f/64 you can still make an acceptable 11x14 from a 4x5 negative (at least in theory.)

The 1/3 - 2/3 rule of thumb cited at the beginning of the thread is probably undeserving of even being called a rule of thumb. As cited, at extreme close ups the depth of field is split equally in front and behind the subject. When you get to the hyperfocal distance, the range of acceptable focus behind is infinite while it is clearly not infinite in front. So the 1/3 - 2/3 ratio is obviously nothing more than an intermediate value chosen to convey the idea that, apart from extreme close-ups, there is considerably more depth of field behind the plane of focus than ahead. That is a good lesson to absorb.

[tgtaylor]

There are other ways to ensure enough depth-of-field that don't require you to stop down and view the image.
My preferred method is simple: After applying whatever movements I need to manage the image, I focus on the nearest object I want to be in sharp focus and note the position of the standards (i.e., distance between the back and front) on the rail or camera bed. I then focus on the farthest object I want in focus and note the position of the standards. I then position the standards exactly halfway between the extremes (note: I don't have to look at the ground glass to do this last step). This is the best spot for optimum depth-of-field. The aperture is determined by how large the focus spread (the distance between the extremes of near and far focus) is. It helps to have some way to measure the focus spread. My field cameras all have millimeter scales added. You can find millimeter rulers on the web and simply print them on an adhesive backed label and stick them on your camera. Heck, you could even make pencil marks on tape and stick that on your camera; whatever works for your set-up.

This is essentially the method I use to focus 35mm and my medium format Pentax cameras and learned of it from a Galen Rowell book. Once you have determined where those two focus points fall on the lens you simply position the lens exactly half-way between them and choose the f-stop marked on the barrel that encompasses both points and add a little extra for insurance.

However for LF you don't have to do all that. Depending on the type of camera you have (base or axial tilt) simply choose one point, say the furthest - even infinity - and focus on that point. When it snaps into sharp focus (check it with the loupe) tilt the lens until the nearest point snaps into focus (this could be a swing depending on where your points are located). Then refocus on the first point and then back on the second point. A couple of reiterations should do it. Then stop down for anything that's soft between those two points. You can see the effect of stopping down on the GG. I think Fred Newman (?) of the View Camera Store describes this method in a video on his website.

Thomas

[Doremus Scudder]

... However for LF you don't have to do all that. Depending on the type of camera you have (base or axial tilt) simply choose one point, say the furthest - even infinity - and focus on that point. When it snaps into sharp focus (check it with the loupe) tilt the lens until the nearest point snaps into focus (this could be a swing depending on where your points are located). Then refocus on the first point and then back on the second point. A couple of reiterations should do it. Then stop down for anything that's soft between those two points. You can see the effect of stopping down on the GG. I think Fred Newman (?) of the View Camera Store describes this method in a video on his website.

Thomas

Thomas,

What you describe works for some situations, but not for others. Tilting to get near/far is impossible if the near and far objects are in the same line (e.g., a near branch and a distant horizon). I cases like these, you just have to rack back and forth. Also, if there are tall near objects in your scene, tilting will increase the focus spread, requiring a smaller aperture to get everything in sharp focus. It's better to apply whatever movements before the final determining of optimum aperture. During this process, one can see what amount of tilt is best. Often, you can reduce the focus spread with a judicious tilt/swing, but not always.

Best,

Doremus

[Vaughn]

I did have a lot of fun with front tilt out in Death Valley this month. In the redwoods, tilt is used sparingly...dang those tall trees! For the two weeks in the desert I did find myself always having to reduce the tilt after my initial adjustment...too gung-ho with the tilt! I am only a third of the way thru developing my negs. (a wind storm kept me from developing last night -- too much chance of losing power). So far so good. An obvious focus/tilt error in the Alabama Hills on one 8x10 (getting use to a 360mm!) The foreground was not equally distanced from the camera -- missed that (double/triple check those corners!)