Infinity focus problem

[Krzys]

It seems that on my Mamiya 645 super with both the 2.8 and 1.9 80mm I cant get to infinity focus on the camera. When looking through the magnifier I can see the split prism is just a touch out of lining up. Is this a problem with my groundglass?

 

[Sirius Glass]

Is the groundglass level and sitting squarely on the surfaces?

If the groundglass is not in proper alignment then the focus can appear to be off when it is focusing correctly.

Open the lens and put groundglass on the focal plane to check the focus.

If the groundglass is not properly aligned you will need to have a repairman align it for you. By the way, this does happen to other reflex cameras, it is not a reflection on Mamiya.

Steve

 

[Krzys]

How severe will this problem affect my focusing at close distances and how do I put groundglass on the focal plane?

 

[Sirius Glass]

Hold the groundglass in place with you hand. Be careful because it is fragile and can crack, chip or break.

Steve

 

[Krzys]

I just did a test. The minimum focus distance of the lens is 70cm. Drew out a tape measure to 70cm and hooked it to an object. I then aligned the camera's focal plane where the film sits with the end of the measure. The object was out of focus and when I moved it to about 65cm from the object (with the lens focused at 70cm) it came into focus.

How can I adjust the ground glass to fix this? How did it happen in the first place!

 

[John Koehrer]

5mm is a pretty gross error. I doubt that there's enough adjustment at the GG and the error is in the lens.
It's very likely that the focusing ring or infinity stop in the lens has slipped.

 

[Dave in Kansas]

I have a Pentax 645 that had a similar problem when I got it. All of my pictures were focused a little off from where I had focused. I took it in for repair and believe it was the mirror was that out of adjustment. The camera appeared to have been used very little when I got it, with no signs of being dropped or abused. I can't imagine how it happened.

Dave

 

[keithwms]

Is the ground glass the right way around... and is it the original mamiya ground glass and holder?

 

[Ian Grant]

I have two Mamiya 645's a plain 645 & a 100S (early models) the second body the early 645 had focus problems with all my lenses, it wasn't noticeable except with fast aperture. In the end I placed a ground glass screen across the film gate with the camera back open and checked the focus the finder screen was way out, there were two adjustable screws and it was quick & easy to rectify the problem, focus was spot on after that.

Ian

 

[MattKing]

I just did a test. The minimum focus distance of the lens is 70cm. Drew out a tape measure to 70cm and hooked it to an object. I then aligned the camera's focal plane where the film sits with the end of the measure. The object was out of focus and when I moved it to about 65cm from the object (with the lens focused at 70cm) it came into focus.

How can I adjust the ground glass to fix this? How did it happen in the first place!

I'd suggest doing the same test with a distant object - something that is effectively at infinity.

If you get an in focus image with the distance scale showing a closer distance, you will know that the scale is out of position. If you cannot get an in focus image, it may be that the infinity stop is in the wrong position, and is stopping the helical focusing from retracting far enough.

Two questions - in your original post you indicated that the split image focussing aid wasn't lining up correctly when focussed at infinity.

Was the image on the surrounding ground glass sharp?

Are the distant objects in focus on your negatives when the ground glass image is in focus?

If it is just a problem with the split image focussing aid, it might be that you need a diopter for the finder.

Matt