Michael, Bart and Cem,
What glass focus screens are you using in your viewfinder for manual focus or are you using the live view? Do you choose one from Canon, the Ec-B, or perhaps a split screen from Brightscreen? I need all the help I can get!
Hi Asher,
I use the EC-s Focusing screen from Canon on my 1Ds3, but check for other codes for other camera models. This is a high precision focus screen specifically useful on lenses with a wide aperture (f/2.8 or wider). Nevertheless, I don't switch it when use it with the f/3.5 TS-E. Yes, the viewfinder gets a bit darker, although it's a large bright viewfinder to begin with, but it's very sharp. One just needs a bit of light to be able and reliably focus with it. For unshifted focusing, one can also use the focus confirmation and the lens can be AF microadjusted even though it's a manual focus lens. I even get useful focus confirmation when using tilt, but it may be less accurate so one needs to check on the specific camera used. One can also use a focusing screen with a grid on it, but that only helps when shooting a symmetrical object exactly from the front or a subject with real vertical lines.
However, eventhough it's a wide angle lens, the focus plane is still reasonably narrow (assuming one needs large output). So I recommend to use Live View whenever possible, in particular when tilt is involved. This becomes very important even with flat facades of buildings, but whether that's due to field curvature or mis-alignment remains to be seen. Due to the wide angle of view, even a small non-parallel alignment between sensor and plane of focus will amount in a significant mismatch of the focal plane at the edges. Michael uses a 1Ds2 without the benefit of Live View, so it's near impossible to detect that on site (unless one shoots tethered).
A simple test for curvature of field is to shoot a high detail surface at a very shallow angle at f/3.5. Although at that aperture one loses some edge sharpness, one still can determine if the plane of best focus is a straight line or a curved one. Try focusing across the center and near the edges to get an idea of what's happening.
When introducing tilt, all bets are off, and one really benefits from Live View. It can sometimes take a bit of searching to align the plane of focus with the most important features in the image, but the bokeh is very smooth and unintrusive so the transition between focus and defocus can be subtle. There are tables that one can use to get an approximate required angle, but nothing beats Live View:
Click on the image to go to the website
Cheers,
Bart
.
