There are situations where neither a tilt nor a swing will suffice to put the exact subject plane where you want it, and from time to time people post questions about what to do if that is so. I've come up with a method I haven't seen elsewhere, which I will describe below. It appears to work in a test. I would appreciate any comments.
To avoid complications, let's assume the rear standard is vertical and level, and that the front standard will be used for tilt and/or swing. (The method will still work otherwise, with appropriate modifications.)
If the exact subject plane includes a horizontal line parallel to the film plane, you would use a tilt. If it contains a vertical line paraallel to the film plane, you would use a swing. Suppose neither of these conditions are met. Then you have to combine a tilt and a swing. In general, not every possible subject plane is obtainable. But, if you could obtain such an exact subject plane by rotating the standard about some arbitary axis, then you can also obtain it by a combination of tilt and swing.
Which should you do first? This will depend on the circumstances, but one way to decide is as follows. If the desired exact subject plane is more horizontal than vertical, tilt first. If it is more vertical than horizontal, swing first. Generally the second motion will be less than the first if you follow that rule.
Let's suppose you decide to tilt first. Start by using near and far points to choose the tilt so that those points are both in focus. This can be done different ways, which have been described elsewhere. Next locate the line where the ultimate exact subject plane intersects the subject plane you obtained by tilting. This will project on the gg to a vertical line. It may be better if this line lies close to the center of the field, but it isn't essential.
Make sure you have the reference line in good focus, at both ends (and in the center for a check.) Next choose two points on either side of that line which you want to lie in the exact subject plane. Make sure the line connecting them intersects the reference line. Now swing so as to bring both those points into focus. As you swing, the reference line may go out of focus, but refocusing should bring it back into focus. Iterate until you get the right and left points simultaneously in focus with the reference line. (Note. You should swing towards the side where the higher point proejcts on the gg and away from where the lower point projects.)
When you are satisfied that you have the exact subject plane where you want it, you may then want to decide how far to stop down. For this, choose two points on either side of the exact subject plane which you want in adequate focus. Focus on one, then on the other, and measure the focus spread between them. Then use your favorite method, e.g., Hansma's Table, to determine the f-stop. Refocus to put the exact subject plane back where you want it and proceed to take the picture.
If you decide to swing first, the reference line would project back to a horizontal line on the gg. Otherwise the method is the same with appropriate changes of language. Also, keep in mind that any rise/fall or shift will change what you should take as 'the center of the field.
In my test run, I was tilting first, and it was pretty easy to identify the vertical (on the gg) reference line. But clearly, this is the essential part of the method, and I don't know if it will always be easy to see it. One approach would be look at the two reference points chosen for the swing and to imagine the line through them intersecting the subject plane arising from the tilt. The desired reference line passes through that, and it would only be a matter of finding detail near its ends to help keeping it in focus as you swing. In my test, the whole thing took me less than five minutes, and with practice I think I could do it in a minute or two. Contrast this with the experience of the person who said in a previous discussion that he fiddled for 45 minutes trying to combine tilt and swing and never got it right.
Reply With Quote
Bookmarks