Midground unsharp - why?

[Leonard Evens]

Eric,

I got my flexible tape with adhesive back from a local store that specializes in woodworking shop tools. I believe you can get one at amazon.com. (See
http://www.amazon.com/Biesemeyer-79-...7?ie=UTF8&s=hi)
You could look in your phone book for a local store which has such a tape or can order one, or you can search the web for other sources.

The tape comes with English units on one side and metric units on the other, but it is not hard to cut it down the middle to produce a metric only scale that fits more easily on your camera.

Amazon also sells flexible fiberglass metric tapes which you could attach using double stick tape.

One thing you might also consider is adding an additional scale to your focusing knob. Because of the gearing, this may allow finer adjustments. See my article
http://www.math.northwestern.edu/~le.../dof_essay.pdf
for an explanation of how I did that for my Toho FC-45X.

As to your basic question, remember that the region in adequate focus is a wedge centered on the so-called hinge line. If you tilted the back, the hinge line would be in a plane parallel to the back and some distance below the lens. That distance depends on the tilt, being large for small tilts and getting smaller for larger tilts. The DOF region has small vertical extent close to the lens which increases linearly as you move further from the lens. As you focus, the whole wedge swivels on the hinge line. If the midground dips below the foreground and far distance, it would be easy for the midground to fall outside the wedge while the rest of the scene would remain in focus. You might be able to get in focus simply by rotating the wedge downward by refocusing, but in that case you would run the risk of moving the foreground or background out of the DOF wedge.

I've made some rough estimates from the data you gave. I think you would have to tilt something like 10 degrees or more to have any chance of getting the foreground in focus. But then at 15 feet the vertical extent in focus would only be about 1.6 feet. Depending on the topography, it might be very hard to get the dip in focus while still keeping both foreground and background in focus.

[Brian Ellis]

"Can anyone suggest a commercial source for a durable mm scale, with an adhesive back and miniscule thickness?"

Many tape measures that you can buy almost anywhere have inches on one side and mms on the other. You don't need an adhesive back. I bought a little pocket-sized cloth tape measure, I forget where but probably Home Depot, that had mms on one side. I cut it to fit along the length of the camera bed and then attached it with Scotch tape. If you happen to have a Linhof Technika you're really in luck because the tape can be cut to fit into the distance scale holder which you can slide out a little ways to facilitate it's use with longer lenses and there's already a pointer built into the camera.

[CXC]

This happens to me all the time. Some images just cannot be brought into complete focus via tilt.

[Tom Westbrook]

There's an article on the home page with some guidelines for f-stops to use for given near-to-far focus difference. http://www.largeformatphotography.info/fstop.html

[Hans Berkhout]

metric graph paper (yes, in mm). Cut off a narrow strip and attach to edge of camera bed with Magic 3M or Scotch tape. Tape should have matte surface, not shiny- so you can mark it as needed with a fine felt pen.

[PViapiano]

Here's a great resource for printable paper rulers in PDF and PS formats. These are great for the above use!

http://www.vendian.org/mncharity/dir3/paper_rulers/

[John Hannon]

Here's a great resource for printable paper rulers in PDF and PS formats. These are great for the above use!

http://www.vendian.org/mncharity/dir3/paper_rulers/

Very useful, Thanks!

[Eric James]

Excellent PViapiano!

[Eric James]

FWIW, here it the shot in question. The "mystery" of the unsharp mid-ground was solved early in the thread, but I said I'd post a jpg when the scan arrived. The subject is Finger Mountain on the Dalton Highway, 15 miles south of the Arctic Circle - no USM.

[Eric James]

I'd like to thank you all again for your advise offered here. This situation rears it head frequently in my compositions and these answers remind me that, although I can chose the two-dimensional plane of focus, I may need to stop down more than I would like to extract sharpness from the third plane. Many of you find your time under the dark cloths to be a rewarding experience, but my back aches, my legs cramp, and my mouth turns foul – now, when the mid-ground remains unsharp despite my tilting and shifting gyrations, I think of this thread and stop-down a bit more.