Infinity focus questiongreenspun.com : LUSENET : Large format photography : One Thread
Hello all, I'm having a hard time getting a sharp image at infinity and close to infinity. I'm using a Century Graphic with Schneider 105/4.5 Xenar and an RH8 back. The back is in good shape and I keep the film tight while loading. Image softness is minor but 'soft' none the less. For a 6x9 image it's simply not useable.
The softness is even across the board (frame) on all frames. The GG matte is facing forward (towards the lens).
With a cheap caliper I checked the difference between GG mounting (front of glass) and film plane mounting. They are very close if not right on. Though the caliper is very cheap.
I spent a couple hours the other day setting the infinity marks so the GG was sharp across the board. It's possible the tree line I used was only a quarter mile away instead of half, but the images I shot later that day were at about the same distance if not a little closer. They are all soft.
My exposure was 1/60 - f16/f22 and I did not use a cable release. I wish I had but I didn't. I'm new to large format but I've been shooting for a long time, including 14 years at dailies, and this softness just doesn't look like camera shake to me. I'm going to do the old 'down the fence' focus test and see what that tells me.
NOTE A: I did shoot a close-up shot a couple weeks ago(camera on a tripod, inside the car, shooting a plastic whale on the dash in a rain storm, no cable release, f16 - 1/8), it's not razor, but it's sharper than my treeline.
Here are the questions: Could this lens be falling apart, some kind of image dispersion at small aperatures? Note A makes me think not.
If I were close to infinity but maybe not exactly on, wouldn't depth of field carry it (especially at f16/22)?
Does 'depth of field' reciprocate to the rear of the lens, back to the film plane? ie: smaller aperature=less film plane distance preciseness?
Could not using the cable release give me a slight softness or rather a dullness around what should be sharp edges? An example would be that the edges of leaves and tree branches simply aren't nice and razor sharp.
Thank you, DL
-- Dennis Lee (email@example.com), October 15, 2000
Welcome to the crowd, Cap'n. Same thing happened to me when I tried to downsize from 4x5, but with a RH-10 back which is supposed to keep the film flat. Well, it don't! Check your negatives and you will find stuff in focus, it just ain't where the image looked sharp on the ground glass. I hear that the Horseman roll film backs are much better. You can verify this by shooting a couple of sheets of cut film.
-- Bill Mitchell (firstname.lastname@example.org), October 15, 2000.
Take a few shots at infinity with regular 4x5 filmholders to determine if it is indeed your rollfilm back.
-- Doremus Scudder (ScudderLandreth@compuserve.com), October 16, 2000.
My bet is that it is not your lens. That's a pretty sharp lens for 6x9 at f22. You will need to do some experimentation, but one thing I would try is focusing on a football field or something at 30 yards and seeing if the film records the same thing or focuses somewhere else.
Perhaps your film and lens plane aren't quite parallel?
And you can examine the flatness of a spare roll of film in the film back.
Shoot a few rolls and play around with it; you'll get to the bottom of it. The lens won't cover 4x5 at infinity (I don't think) but it should get close and the advice above to shoot some 4x5 is probably the first thing I'd do. Good luck.
-- Erik Ryberg (email@example.com), October 16, 2000.
I noticed a problem with "softness" in my images as well. Problems with bricks in a building, ladders, leaves, rocks, the whole bit. I have a Graphlex Super Graphic, and it turns out that my focal plane and film plane are not within tolerances.
I have a decent quality dial caliper, and I noticed that my GG is a tiny fraction forward of my film.
Take some cardboard and newspaper. Make a series of steps with the cardboard, at least an inch tall. Paste newspaper onto the steps. Focus on the middle step, and then make a photograph. Look at the negative. Is your middle step in focus, or is one of the other steps in focus?
I found out on mine that one of the other steps (near the end) is in focus, so I need to shim my ground glass. Depth of field will not carry you in this situation. It only does you good when the film and glass are in tolerance.
-- Brian C. Miller (firstname.lastname@example.org), October 16, 2000.
There is another variation of the test mentioned above. Instead of steps, make a ramp and paste something with good quality type onto the ramp. Mark one of the lines near the middle of the ramp as your focus target, and go through the trial shooting some film at wide apertures. I remember being able to see the focus difference between adjacent lines of type.
-- Larry Huppert (Larry.Huppert@mail.com), October 17, 2000.