I have a 90mm angulon 6.8 which should just cover 4x5. The problem is that I do not know when my front standard is centered ( ie how much rise/fall) so that I could set the lens to the optimal projection of the image circle on the ground glass. Could anyone help me determine this? (I don't have a centering mark on the front standard).?
Run the front standard back as close to the ground glass as you can get it. You should be able to see the back element through the ground glass; if not, remove the ground glass. Measure from the edges of the rear element to the top and bottom of the gg (or its frame). That'll tell you how far off it is in that position. It may be centered or you may have to move it up half of the difference between the two distances once you have the bellows out. Then mark that centered position on the front standard for future reference.
Hope this makes sense...
"I love my Verito lens, but I always have to sharpen everything in Photoshop..."
Makes sense Mark. Will give it a shot! Thnx
Another method is to make a mark on a wall the exact height from the floor as the centre of your ground glass. Looking through the GG you will be able to see if the lens has to be raised/lowered to make the mark coincide with the GG centre. The camera has to be absolutely vertical, of course. As you're using a wide angle lens, about 10' between wall and camera should be plenty, although a longer difference will give better accuracy.
Barry.
For quick centering in the field, match up all 4 crescents you see through the ground glass cutouts so that they are all about the same size.
Thnx for the suggestions. The wall method might be difficult as it requires a number of accurate measurements. I have noticed there might be another way. I just compressed the bellows to the maximum and they self centered the front rise/fall (which were unlocked), this offcourse would require that the bellows themselves were centered and not warped. Ic-racer, could you please explain your duggestion a bit more? I am having trouble understanding what the crescents are??
Originally Posted by ic-racer
Just be aware that on some cameras they are centered, and on some they may be a little high or low. That's why you should do a quick measurement from the lens rim to the edge of the frame to see things are equal.
"I love my Verito lens, but I always have to sharpen everything in Photoshop..."
Place a mirror across the front of the lens, with the mirrored face inwards. Then shine a bright, focussed light onto an off-center spot on the ground glass (a laser pointer works well too). Focus until an in-focus second light spot appears opposite the first: halfway between the two is the optic axis. Move the lens until the axis is at the center of the screen.
This assumes that your angular movements are accurately nulled. By checking that the spots are evenly distributed either side of a constant point as you move the first one around the ground glass you can check for that too.
Measure where is the centre of your gg. Put a mark (scotch etc.) on the side of your back standard. Measure where is the centre (axis) of your lens, make a mark on its side too. Compare the two marks.
Don't forget to mark the rear element with a cross-hatch once you find the center, all the best photographers do this. If you can't afford the $129 Rodenstock Centering Etching Device, you can usually use the corner of a small mill bastard file held at a 45-degree angle. Use a steady hand and just etch the rear element enough that you can feel the indent. Then you'll be able to see the cross hatch on your GG and always be optimal.
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