Tilt in an urban enviroment

[Bill_1856]

I just realized that despite being posted on the LF forum, 6x12 ain't in inches but in mm, (like a letter-boxed 4x5 negative).
I don't see any problem -- just KISS.
Hyperfokal distance for a 135mm lens at f:32 is 12.5 feet, and daylight exposure for ISO400 film is 1/100 sec @ f:32.
Just shoot on Ilford HP5, set your lens at f:32 (diffraction isn't really much of a problem) and your shutter at 1/100 (which is fast enough to stop any people motion), and focus at 12.5 feet (there's nothing in either image closer than 6 feet).
I don't see that there's any problem, no lens tilts, etc are required (you might need to use lens rise to keep the verticals parallel).

[Ben R]

Bill, the hyperfocal distance for a 135mm lens with 4X5 @ f32 is 19.1 ft with a near DOF of no closer than 9.5 ft.

I don't know what the CoC of 6X12 film is but I would assume that it was even less forgiving than 4X5, possibly nearer that of 6X9.

Either way...

[Bill_1856]

http://bobatkins.com/photography/technical/dofcalc.html

[Ben R]

I used DOFMaster, should we let the software fight it out or does anyone want to adjudicate?

[jb7]

Isn't depth of field dependent on your final print size?
Perhaps the software is not equally ambitious-

j

[Lachlan 717]

Isn't depth of field dependent on your final print size?

j

As far as I know, no, it is has nothing to do with print size... It is a core relationship between focal length and relative aperture.

Once the image is captured, even out friend, USM in Photoshop, won't fix a poorly and/or limited-focused and “apertured” image.

[jb7]

One of the best ways I know
to increase depth of field
is to print smaller than usual...

j

[Ralph Barker]

DOF has everything to do with print size, since it is a function of enlargement - the point at which a defocused fuzzy circle (circle of confusion or CoC) will still appear to be a point. Viewing distance is also a factor, as is the average resolving power of the human eye.

Most/many DOF calcutors assume a print size of 8x10 and a viewing distance of 250mm, and assign different CoC values to each film format size based on the degree of enlargement required to produce an 8x10 print. Some are more conservative with the CoC value, some more liberal.

Since the target print size is 20" x 40" from the 6x17 negs, it might be more reliable to manually calculate the CoC from the diagonal of the target print size, and modify a DOF calculator accordingly. Or, one might just use the CoC for 6x6, based on the assumption that the narrow dimension will produce more conservative (closer to "tack sharp") results.

Wikipedia has a fairly good explanation:

http://en.wikipedia.org/wiki/Circle_of_confusion

[David A. Goldfarb]

Or alternately, if you plan to print big or otherwise have different standards of sharpness, stop down one or two stops from the calculated recommendation, which is what I do.

[Leonard Evens]

DOF has everything to do with print size, since it is a function of enlargement - the point at which a defocused fuzzy circle (circle of confusion or CoC) will still appear to be a point. Viewing distance is also a factor, as is the average resolving power of the human eye.

Most/many DOF calcutors assume a print size of 8x10 and a viewing distance of 250mm, and assign different CoC values to each film format size based on the degree of enlargement required to produce an 8x10 print. Some are more conservative with the CoC value, some more liberal.

Since the target print size is 20" x 40" from the 6x17 negs, it might be more reliable to manually calculate the CoC from the diagonal of the target print size, and modify a DOF calculator accordingly. Or, one might just use the CoC for 6x6, based on the assumption that the narrow dimension will produce more conservative (closer to "tack sharp") results.

Wikipedia has a fairly good explanation:

http://en.wikipedia.org/wiki/Circle_of_confusion

Ralph's analysis is right on the mark. I would only add that, as Ralph said, one has to make some assumption about the distance from which that 20 by 40 inch print is going to be viewed. The usual rule of thumb is that viewers get back a distance about equal to the diagonal of the print. That means you get the same depth of field for all prints viewed in that way. That means in turn that you can base your depth of field calculations just on viewing a fixed size print such at 8 x 10 inches at one fixed distance such as 250 mmm.

Actually, I think that 250 mm is a bit close. for viewing a print. Only relatively young people can see clearly that close. As we get older, we get bifocals or the equivalent, and the normal reading distance for such lenses is usually set to about 16 inches. One can usually see things clearly down to about 12 inches, but 10 inches is a bit of a stretch, particularly for oldtimers like myself. Of course, you can have glasses made for closer viewing, but you have to request them specially. I have two different pair of bifocals, one for use with a computer, which are set for different reading distances. I also have a special pair set for viewing at about 6 inches. I use that when focusing on the ground glass. That has two advantages. first it is roughly equivalent to a 2 X loupe and also it corresponds to viewing an 8 x 10 print from about 12 inches, which is my normal viewing distance for such prints.

Of course, many people will insist on getting as close as they can to a print, no matter how large, and for them depth of field, for the limited part of the print they can see that close, will be significantly reduced. To push things to the extreme, you could view a print with a high powered loupe, and you would have practically no depth of field.


.