Post
by Charles Twist » Sun Nov 06, 2011 7:39 pm Etc/GMT-1+01:00
@Andrew:
Yes I can see your point about the left being unnecessary to the story. I don't think I should include any more of the Selfridges bldg, so if I stay in the 5x4 format, then I'd lose the top of the Selfridges bldg. I think the "returning" curve holds the composition together, so I'd have to use a wider focal length and move nearer to the subject. Then you'd lose more of the roof of the church. It's a good idea but requires a move away from 5x4.
@Neil:
Andrew is on the right track. When you shoot a lens with a Petzval formula, the focal plane is curved (section of sphere). This is especially noticible at the wider apertures, such as I have used here. If you photograph a flat facade, you can't have all of it in focus. So I would struggle to get the whole of the steeple sharp. The Selfridges bldg is curious in that it has a curved exterior. So there is a coincidence of two curved planes in this picture. There is some swing on the rear to hold parts of the Selfridges bldg and the steeple both sharp, but I believe it's impossible to have them both entirely sharp at f/5. I would have to stop down to achieve that - then you lose the curious character of the Petzval, which still fascinates me enough to indulge it. One day, I'll grow up. Right now, I am enjoying myself. You'll also see that the corners of the picture are soft - that's due to the image circle.
Regards,
Charles