Mike's Photography Page

SRT Focus Issues Page

Focus Accuracy on Film Plane

One way to check this requires a second camera equiped with a long lens.

Mount a normal (around 50mm) lens that has properly adjusted focus on the camera and set focus to infinity.
Open the back of the camera.
Tape across the film plane with clear tape that has a checkerboard pattern written on it.
Make sure the tape is flat and on the same plane as the film would be were it in the camera.
Put the camera into "B" mode and use a shutter release to lock the shutter open.

Look through the front of the lens with the second camera set to infinity focus from a close distance and see that the lines are sharp and clear. The picture here shows a sharply focused pattern on the tape.

Adjust the focus of the camera under test and examine the results to prove to yourself that the camera's focus is accurate. The picture here is an example of what would be a soft focus situation, though it was created by moving focus of the camera under test off of infinity.

I've never had a problem with this test, so cannot make a recomendation as to proper way to adjust, if things are not good. The adjustment screws are under the leatherette on the front of the camera, if it makes a difference.

Viewfinder Focus Accuracy

First check for film plane focus accuracy.
Place a lens with known good focus on the camera.
Set lens to infinity focus.
Look through camera at a distant object that has a clearly defined edge. Examples might be the edge of house, or tops of trees against the sky.
If focus doesn't reach or passes infinity, you must correct focus.

Remove camera top.
Loosen viewfinder hold down screws.
Adjust each of the three viewfinder adjustment screws an equal amount in the same direction.
Repeat until camera focus is accurate at infinity.
Tighten hold down screws and recheck focus. Tightening hold down screws can affect focus, so be sure to check before you replace camera top.

50mm f1.7 MD Lens Focus Accuracy Repair

I recently received a Rokkor 50mm f1.7 MD lens with that had it's focus setting out of adjustment. The fix was surprising easy.

First remove the plastic housing on the front of the lens. This can be achieved with a rubber cork of the right size or even a rubber floor protecter as I show here. The rubber piece must fit over the plastic ring, but not touch the front glass of the lens.
Once the plastic housing is removed, just loosen the three outer screws. There six screws here, but three are recessed. The recessed ones do not need to be touched.
The focus adjust ring will now move independantly of the front lens element.
Adjust by moving the focus ring a bit one way or another while keep the lens still.
Check adjustment by mounting the lens on a camera with known good focus adjustment and viewing a distant object with distinct lines in it. This could be tree tops against the sky or the edge of a house.