Hi Joanna, I'm just starting out with large format. So bear with me. My 4x5 camera is a Chamonix 45H-1. It has asymmetric tilts and swings. I believe I'm suppose to focus on the 1/3 line (upper or lower line?) then tilt (the front or rear?) until the other third line comes into focus. How does that work as opposed to your method of focusing on the nearest and tilting to the furthest?
In my opinion, asymmetric movements are only useful when you have a "standard" scene to photograph. If you don't want the plane of sharp focus to pass where the ⅓ line is on the ground glass screen, then you will need to use the part of the screen that does pass where you want the line of sharp focus to be.
Sometimes I start on something in the distance, sometimes on something near - it really makes no difference and you will soon work out which works better for you with the type of scene you are photographing.
I would highly recommend you read
Harold Merklinger's books on focusing the view camera - they are a mine of interesting and useful stuff, including movie animations of how the "wedge" of focus changes with movements.
The books are available as PDF downloads and there is plenty of other stuff on linked pages.
The problem with trying to apply DOF calculations to movements is that the DOF changes the further away from the hinge point you move. As I alluded earlier, the zone of sharp focus is wedge shaped, starting from a point near the camera and getting wider as it travels away from the camera. So, your calculation tells you that, with a 150mm lens, at f/16, the depth of field at 12m is 69m (5m in front and 64m behind) - your problem is, because the plane of sharp focus is at 15° from the horizontal, that means that you have to measure the DOF along a line that is 75° from the horizontal, 12m away from the camera.
Which is why, in general, if you are using tilts or swings, forget calculations and simply rely on what you see on the screen.
Always start by determining where you want the plane of sharp focus to pass through, at full aperture, then stop down, inspecting the screen to see when everything else of importance becomes acceptably sharp. The rule of thumb that I was taught about minimum aperture was 2 stops larger than the minimum on the lens/shutter.
Don't forget, when we talk about diffraction limitations, acceptable sharpness is relative to the size of print, the viewing distance and the eyesight of the viewer. If we are talking about a 50" x 40" print, only the ardent "pixel-peeper" will walk right up to the print to check that the eye on the fly on a plank of wood is sharp enough. Most people stand further back to take in the whole image.
St Mary's, Saffron Walden par Kris Lockyear, on ipernity
