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How Shift Lenses Change your Life
If you externally meter, then a meter reading good for a centered shot will be too short an exposure for a
shifted shot. How much too short? Who knows, bracket! 8-) On the other hand, the camera meter
depends on taking readings of light off of partial reflections, and depend on the angle the light hits the
sensors. When you shift, the light comes from a different direction and the sensors may see none of it (or
too much), so they will suggest a bad exposure.
How to Get a Good Exposure
If you don't want to bracket, you need to build up some base-line cos^4 data for your lens. Perhaps the
following might be agreeable:
1. Build comparison series: on slide film, photograph a grey card metered with 0 shift and no
exposure compensation, then -1/3, -2/3, -1, -1 1/3 stop. (either internal meter or external is fine)
2. Find worst-case dropoff: shift maximum (horizontally if you can shift sideways), and use the
same shutter and aperture as the first shot of your comparison series.
3. Develop these shots.
4. Using the center of the series shots, determine whether the maximum shift is -2/3 darker or
whatever. That maximum shift is 36mm(width)/2+11mm(shift)= 29mm from image center. If
you want, measure the falloff at other distances.
Then: after metering a scene with a handheld meter or unshifted lens, set the exposure manually but with
the test-result compensation. This should be perfectly accurate with one caveat: Because the darkening is
progressive, the maximally-shifted side will always be somewhat darker. For arrchitecture, this is perfect
- it saves you from using an actual graduated filter to bring the sky and ground brightness closer.
Since you may not be able to see this difference in the viewfinder, your probably still want to bracket,
but bracket from the external/unshifted exposure to your test-result maximum compensation. Some
picture in that range should be ok.
Wish List
The only return I get on writing an article like this is the right to voice my own opinions - and hopefully
Canon's listening!
New Lens
More than anything in the world, I want a 35mm tilt-shift lens. The gap between the 24mm and 45mm is
just too great. And, the 24mm is not sharp enough to have its images cropped 50% without pain. This
lens physically works with the Extender EF 1.4x teleconverter (TC), but resolution seems to suffer
somewhat. In effect, the TC creates a very expensive, 35mm f/4.9 lens with less than ideal sharpness.
http://www.photo.net/photo/canon/tilt-shift (7 of 9)7/3/2005 2:24:04 AM