Confessions, DOF & One's Aging Eyesight

[Raymond Bleesz]

I'm in a dilemma--perhaps someone can offer a suggestion or two. My increasingly poor eyesight has me avoiding going through the rituals of tilting to obtain DOF (I find I can not identify on the ground glass where max DOF exists, by eye glasses or loop---perhaps I'm not concentrating enough, or perhaps I'm getting lazy or perhaps???). However, with loop hand, I am able to focus on an object in the near/far 2/3rds concept in the scene, allowing for some DOF dependant upon f stop, etc. In such situations, the "near" is usually soft while the "far" is in better focus.

Are there other forum users in the same dilemma or can one offer suggestions, etc?

This may read as dumb, but that's what is on my mind.

[ic-racer]

Not sure about the 'thirds' thing, but mathematically the best place to set the focus is to place your focusing standard half-way between the near and far point you want in focus.

[MIke Sherck]

When near focusing gets bad enough, consider one of the eyeglass loupes favored by jewelers. It's a magnifier which clips onto the eyeglasses, so you don't need to hold it up there with a hand.

Yeah, I know how it looks. *Sigh*

Mike

[Leonard Evens]

Just what do you mean by `increasingly bad eyesight'? Is it that you are just experiencing loss of near vision due to normal aging, or do you have some other problem?

In the first case, I would suggest getting some reading glasses corrected so you can focus at 6 to 8 inches from the screen and use them for focusing. Also, try getting a loupe which can be placed against the screen and focused.

The near far method, which I will describe below doesn't depend on jusging what is or is not in focus.

For no-tilt/swing situations, you pick a near point you want in focus and a far point. You focus first on the far point, noting the position of the standard on the rail, and then on the near point, doing the same. Measure the distance in mm between those two positions. Then multiply that distance---called the focus spread--- by 10 and divide the result by 2 to get a lower estimate of the f-stop you need so that both near point and far point will be in focus. If you stop down one additional stop beyond this lower estimate, you will be fine in most situations of moderate focus spread, say up to 6 mm. If the focus spread is very large, then diffraction may begin to be an issue. In that case, you can use the more advanced methods at /www.largeformatphotography.info/fstop.html

If you tilt, the situation is more complicated. First you ahve to decide how much to tilt. For that purpose try to visualize a plane extending out in space which passes roughly halfway through the region vertically and horizontally that you want in focus. Pick a near point and far point in that plane. Start off with a guess at the tilt, say about 5 degrees. Focus on the far point. then focus on the near point. If you have to increase the distance between the standards to do that, increase the tilt. If you have to decrease the distance between thestandards to do it, decrease the tilt. After a few iterations of this procedure, you should find that the near point and far point are both in focus at the tilt you end up with.

Next, to determine the required f-stop to get everything you want above and below this plane in focus, proceed as follows. Choose a high point above that plane and a low point below it, focus at each, noting the focus spread between them. Then use the same rule as described above for the no-tilt case, to determine a lower estimate for the rrquired f-stop.

[Bill_1856]

Just stop 'er down and don't worry about it.

[William McEwen]

Two ideas...


Does your camera have rear base tilt? Richard Ritter and Bruce Barlow will testify that Fred Picker was an advocate of "focus on the far."

Here's how it works.

FOCUS ON THE FAR. With everything level, focus on the thing you want in focus that is farthest from the camera. Line of trees, beach, whatever.

THEN TILT the top of the back toward you -- stop tilting when the nearest thing you want in focus is in focus.

That's it. Just stop down a bit, close the lens, and do the rest.

One word of caution -- As Fred instructed, the stuff closest to the camera LOOMS LARGE. It's extended a bit. This is OK with most landscapes.

I tried it with a full length portrait once, and it wasn't pretty. The woman's foot LOOMED LARGE.

Also, you can get magnifying eyeglasses at Sams and Barnes&Noble. You might prefer those to loupes.

[William McEwen]

Just stop 'er down and don't worry about it.

That's what Stieglitz taught.

"Stop down as far as possible."

[Ed Richards]

Having recently moved from a Sinar F2 to an Ebony, I have been reminded at how nice the Sinar system is for DOF. Just focus on the far, set the dial, focus near, and the dial shows you the necessary f stop and where to crank the focus to for the best midpoint. You might think about moving to an F2, they are pretty cheap, and are great for DOF.

[Nathan Potter]

I'm not quite sure from your description what you have trouble seeing. But it sounds as if it might be related to seeing any sharp focus directly on the GG either with a loupe or closeup glasses. I use an old Linhof screen (actually several) where the frosted area covers all but a center and diagonal strip from center to corner. These strips are clear glass thus allowing direct view of the aerial image with a 5 or 10x loupe. Critical focus is achieved when my eye sees the edge of the frosted part of the screen in sharp focus with the aerial image also in sharp focus (a parfocal condition).
Don't know how available these type of screens are presently but Linhof may still market something equivalent. I don't believe you can do better than this technique for a direct observation of focus providing your eyes are corrected for clear viewing of the screen. Of course it only works for that part of the screen where both frosted and clear parts are within the field of view of the loupe.

Nate Potter, Washington DC.

[Brian Ellis]

I'm in a dilemma--perhaps someone can offer a suggestion or two. My increasingly poor eyesight has me avoiding going through the rituals of tilting to obtain DOF (I find I can not identify on the ground glass where max DOF exists, by eye glasses or loop---perhaps I'm not concentrating enough, or perhaps I'm getting lazy or perhaps???). However, with loop hand, I am able to focus on an object in the near/far 2/3rds concept in the scene, allowing for some DOF dependant upon f stop, etc. In such situations, the "near" is usually soft while the "far" is in better focus.

Are there other forum users in the same dilemma or can one offer suggestions, etc?

This may read as dumb, but that's what is on my mind.

There are too many variables with the 1/3-2/3 thing to make it very useful IMHO. The actual ratio varies with focal length of lens and distance from subject so there's almost an infinite number of variables.

If you can focus at all, as you apparently can, I'd suggest focusing on the nearest thing in the scene that you want to appear sharp, focusing on the farthest thing you want to appear sharp, measure the distance the front or rear standard (whichever you're using to focus) moves between those two points, then set the relevant standard half-way between the two points. Stop down to the optimum aperture by using a good depth of field table. That pretty much eliminates the guess-work as long as you can see well enough to focus on the near and far. This system is discussed in much more detail in QT's excellent view camera focusing articles in this forum.

I use the Linhof depth of field tables but there are others out there. I usually stop down one more stop than the tables indicate because I may want to enlarge more than the tables assume (it's my understanding that most tables assume an 8x10 print).