[boyette]

Morning all! I recently acquired a 645 and a 135LS f/4 and I started shooting with it and I developed my first roll. From what I can tell, the camera is back focusing. As this was an eBay purchase, the previous owner did not list the screen had been changed out. Do you think an aftermarket screen could cause this issue? I did pull it out and the tab that is used to remove and install it doesn't have anything on it, making me believe it is aftermarket.

Thanks!!

Corey

[Alex645]

I've never switched the focusing screen on my 645 or 645N, although theoretically that could be the issue....or not. It is more likely the lens.

Two solutions:
a) Buy and test it with an original screen. It may be easier to find a non operational 645 and to use it for parts.
b) Run a test with another lens. As we know from DSLRs, front and back focusing often is an issue with individual lenses and not a general condition of the camera.

[Smolk]

I do not remember the screen of the 645, but I do recall that the viewfinder has a diopter correction, and also that it could be loose (or was that the 645N?). In any case, that might be something to check, perhaps with another 645 lens.

[barondla]

I do not remember the screen of the 645, but I do recall that the viewfinder has a diopter correction, and also that it could be loose (or was that the 645N?). In any case, that might be something to check, perhaps with another 645 lens.

Had a manual focus camera once that manually misfocused when using the viewfinder. Finally found out the interchangeable focusing screen was partially unseated in holder frame. Reinstalled screen and all was well.

Thanks,
barondla

[rdenney]

Since the OP has probably already addressed his problem, I'll add this for future posterity who finds this by searching.

The 135LS is not an autofocus lens, so any focusing error cannot be due to the autofocusing apparatus in the camera, UNLESS the operator ignores the image on the ground glass focusing screen and relies solely on the focus confirmation indicator in the viewfinder.

The focus confirmation is the easy diagnostic solution, however. It should precisely agree with the ground glass in the viewfinder. If it doesn't, the fickle finger of fate points to the focus screen, always.

A misadjusted eyepiece won't cause a focusing error, it will just prevent the view of the ground glass from ever being sharp. The key with that is to focus the markings on the focus screen to be sharp.

My first suspicion would be that the focus screen is not fully seated. I would check that first. If it is fully seated, then expose another roll, with some images focused using the screen, and some focused using the focus confirmation light. Keep track, of course. If the screen is correct but the focus confirmation is not, then check with other lenses. If the focus confirmation is correct but the screen is not, then something is fouling the correct positioning of the screen, or the screen is faulty. If both are wrong, check the camera to see if it has been dropped and distorted. Also, check for correct film loading. Film not being held flat in the holder can cause focusing errors.

Rick "focus confirmation makes diagnosis easy" Denney

[Silent Street]

After changing focusing screens in the 645, is collimation required to ascertain accurate near and far focus?
Collimation assesses focus at 3 points on the focusing screen, usually with two lenses: a wide angle and tele.


You should also check that the camera's dioptric correction facility is set to your state of vision.

[rdenney]

No. Focus screens on the N, NII, D and Z (at least) are user-changeable, and the kit comes with a tool. I’ve never owned the earlier models, so I don’t know about them. I did install a microprism spot screen from an N in my Z and it works perfectly.

Rick “didn’t see any way for the screen to be misaligned” Denney

[texandrews]

Maybe the holder isn't holding the film flat?

[Alex645]

Maybe the holder isn't holding the film flat?

This just made me wonder....how is the OP determining there is a focus problem?

Are you inspecting the film with a loupe?
Are you inspecting a contact sheet?
Are you inspecting scans and who made the scans and how?