question about the parallelity (film - lens)

[chris77]

hello apug.
dont know if its the right place to ask this.
when i cleaned my mamiya rz67proII today i found that the upper and lower side of the lens mount seem to be about a millimeter out of perfect vertical parallelity with the body.
i was wondering, as i will start doing macrophotography, if it might be a problem.
the lens i will use is a 140mm sekor z macro lens, with nr1 and/or nr2 extension tube.
wish i could calculte the dof on the film myself, but i am not so good with these calculations - yet!
i am well aware that there will be less dof on the film-level when the focus is on infinity (no bellows extension) as the lens is then closer to the film.

well.
maybe somebody can help me out.

nice weekend to you all.
chris

 

[John Koehrer]

Are you sure that you're measuring to the body casting or to the cover? You would need to get to the casting to be accurate.

 

[Brett Rogers]

It's the relationship between the lens mount and the film rails that is relevant to accuracy of focus. Measurements off external parts of the body might indicate the need for further investigation but aren't normally conclusive in themself (unless of course some sort of catastrophic damage has occurred). Depending on the shape of the camera body if you do not have access to an auto-collimator an external micrometer, a dial gauge and surface plate, or depth gauge, could be used to accurately assess the parallelism between the mount and the film rails. Rollei specified a 0.05mm tolerance for the lens mounts of their TLRs. A genuine one millimetre deviation across the mount would definitely impact sharpness across the film gate I should think. Of course, lateral thinking is always worthwhile. Have you noticed any deficiencies in your developed films? If not, you may be concerned about a non-existent problem.

 

[chris77]

thanks for your answer. well, i dont have the tools for deeper examination.

but what you said..

Have you noticed any deficiencies in your developed films? If not, you may be concerned about a non-existent problem.

so far i am more than happy with the sharpness, so i guess you might be right there.
but just a few days ago the tripod head (with cam and lens attached) tilted forward without me noticing (didnt lock the pan lever well).
it was loud, as the lens is pretty heavy. but i guess a camera like the rz67 is meant to resist a little shock like that.
i am going to run some tests anyway.. (as i have never done so since i bought it)

nice day.
chris

 

[shutterfinger]

Do not rely on measurements to other parts of the body as it may not be square. Get a small carpentry square, example: http://www.harborfreight.com/8-in-x-12-in-carpenters-square-69363.html , place the long side across the bottom of the camera body and the short side against the camera back with the film holder removed. Check close to the outside edges and the center if possible. Note the variation from bottom to top if any at each position tried. Now turn the square 180° and check the lens mount with the focus at infinity and closest rail focus. It should match the camera back precisely. Roll film is 3.5 mil thick for Fuji, 4.5 mil thick for Ilford and Kodak. If the variance between the lens mount and camera back is less than the film you use thickness but not perfect then you are acceptable and may have a slight focus shift from top to bottom that may not adversely affect the image. If there is a variance and it is more than the thickness of the film in use there will be a very noticeable difference in top to bottom focus that will affect image quality. The condition of the film holder and how flat it holds the film may be of more consern than lens mount squareness. Film holders should hold film parallel to the camera back/image plane. A combination square, https://www.google.com/search?q=com...oTCNOuzZaw7scCFY08iAodBzwCmQ&biw=1920&bih=971 , is not suitable for camera checking as the short adjustable portion may have 1° to 3° play causing an erroneous reading.

 

[chris77]

hi shutterfinger.
thats good input!
will do that when im back in town..

Do not rely on measurements to other parts of the body as it may not be square. Get a small carpentry square, example: http://www.harborfreight.com/8-in-x-12-in-carpenters-square-69363.html , place the long side across the bottom of the camera body and the short side against the camera back with the film holder removed. Check close to the outside edges and the center if possible. Note the variation from bottom to top if any at each position tried. Now turn the square 180° and check the lens mount with the focus at infinity and closest rail focus. It should match the camera back precisely. Roll film is 3.5 mil thick for Fuji, 4.5 mil thick for Ilford and Kodak. If the variance between the lens mount and camera back is less than the film you use thickness but not perfect then you are acceptable and may have a slight focus shift from top to bottom that may not adversely affect the image. If there is a variance and it is more than the thickness of the film in use there will be a very noticeable difference in top to bottom focus that will affect image quality. The condition of the film holder and how flat it holds the film may be of more consern than lens mount squareness. Film holders should hold film parallel to the camera back/image plane. A combination square, https://www.google.com/search?q=com...oTCNOuzZaw7scCFY08iAodBzwCmQ&biw=1920&bih=971 , is not suitable for camera checking as the short adjustable portion may have 1° to 3° play causing an erroneous reading.

 

[Xmas]

The acid test is print off several ISO lens resolution test images place at corners of image and take a photo on tripod with flash and inspect with loope or microscope if the left side is sharper than right then camera and or lens have a problem.

Dropping a RB would not be good.

http://www.graphics.cornell.edu/~westin/misc/res-chart.html

 

[chris77]

The acid test is print off several ISO lens resolution test images place at corners of image and take a photo on tripod with flash and inspect with loope or microscope if the left side is sharper than right then camera and or lens have a problem.

Dropping a RB would not be good.

http://www.graphics.cornell.edu/~westin/misc/res-chart.html

nice. thank you.

oh, i didnt drop the camera.. she was well fixed on the pan/tilt head. it just violently tilted forward (because these lenses are heavy) when i had turned away.

have a good day.
c

 

[mdarnton]

You will see alignment errors wide open at infinity much more quickly than in macro work. Turn your camera on its side and shoot a horizon shot with as wide of an opening as possible, and see if either end of the horizon is in focus the same. The reason I say to shoot with the camera sideways is because you're concerned with top-bottom lens alignment. If you shoot a distant scene in the normal position, then naturally things at the top of the photo will be farther than those at the bottom, so you won't be checking focus at infinity at both top and bottom. Normal position is fine for checking left-right alignment.

 

[chris77]

You will see alignment errors wide open at infinity much more quickly than in macro work. Turn your camera on its side and shoot a horizon shot with as wide of an opening as possible, and see if either end of the horizon is in focus the same. The reason I say to shoot with the camera sideways is because you're concerned with top-bottom lens alignment. If you shoot a distant scene in the normal position, then naturally things at the top of the photo will be farther than those at the bottom, so you won't be checking focus at infinity at both top and bottom. Normal position is fine for checking left-right alignment.

exactly.
also a very good idea!!
will do so..


tx