
Originally Posted by
Doremus Scudder
A couple of things:
First, as you found out, when working at a distance from your subject with a 90mm lens, the inherent depth of field afforded by the short focal length ends up obviating the need for lots of movements. With architectural shots like yours, you only really have to worry about making sure everything is plumb and level so the verticals won't converge.
However, when working with longer lenses or closer to your subject, swing can be very useful. When using swing (or tilt, for that matter) note that you have two basic choices: swing the lens stage or swing the back. Note that swinging the lens stage will not introduce any "distortion" into the image, but that you need to be careful that you don't run out of lens coverage, since you are displacing the image circle from center and, especially with lenses with limited coverage, can vignette. With back movements, on the other hand, the image circle stays put, but the size of the image changes: the part of the image that is moved farther from the lens gets larger and vice-versa. This can be useful if you want to emphasize the convergence of the horizontal lines. And, of course, you can always use a combination of the two to get whatever effect you like.
About your image of the Fabric Center: having the corner of the building closest to you and two receding walls presents all kinds of possibilities. However, swinging to align with one wall will throw the other wall more out of focus. Now you may want to do this to emphasize converging horizontals on that one wall, but then you need to have enough depth of field to compensate for the other wall being out of the plane of sharp focus. If you just want a "straight" rendering, then, in this case, I wouldn't use swing at all, just make sure I'm focused in the right place to get everything sharp (I use a "near-far" focusing method.
As for the technique used applying swings and tilts: If you have axis swings and tilts, it's almost always easiest to focus first in the center of the ground glass and then swing/tilt to get the edges in focus. For this technique, you need three focus points for each movement. For a tilt, for example, you'd need a point in the center and then one on both the top and bottom of the plane you want to be in sharpest focus. For swings, you need a center point and one on each side. Focus on the center and swing till the other two are sharp, check, refocus if needed and you're good to go.
If you have base tilts, then it's almost always best to start with a focus point at the bottom of the ground glass (this is usually the "far" point). For this technique you only need two points, one at the top and one at the bottom. Focus on the point at the bottom of the ground glass and then tilt (lens or back, with the same caveats as above for swings) until both your focus points are equally unsharp. Refocus the point at the bottom of the ground glass and then check the top one. If it's sharp, your good to go. If not, tweak focus while watching the focus point carefully (through the loupe is best). Tweak slightly and in one direction only. Say we tweak by making the bellows longer (focusing closer); if the focus on the point improves, that means you have to tilt a tiny bit more in the direction to make the bellows longer (i.e., forward with the front or back with the back). If the focus gets worse, then you need to tilt a tiny bit to make the bellows shorter (back with the front or front with the back). (Vice-versa works too, but I like to standardize on tweaking just one direction when checking focus.)
Note that even folding field cameras, which usually only have base tilts, always have axis swings, so swinging technique is the three-point-focus-in-the-center-first one.
When tilting and swinging, it's really helpful to imagine where you are positioning the plane of sharp focus in the scene and then identifying those parts of the scene that are the farthest from that plane, focus-wise. Choose those points for your focus points for finding final focus and choosing the appropriate aperture.
Hope this helps,
Doremus
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