Pentax 645 Focus Problem

[Dave in Kansas]

A few years back, I had an opportunity to pick up a Pentax 645 that looked to be in good condition. It was very clean with no dings or visible signs of wear. My first roll of film through it indicated my focus was off so I had a local repair shop work on it, and I thought it was fixed, but I never confirmed it. I have a Mamiya system that I normally use, so the Pentax hasn't been out much since I've owned it.

I recently confirmed that the focus problem has not been fixed, so last weekend I set up some white dry erase boards and noted various distances and f-stop settings as I changed distance with the camera. I used a measuring tape to check the distance from the film plane to the focus point. The camera was mounted on a tripod and I focused very carefully. My test confirmed that the camera is focusing well beyond what the split imaging focus indicates in the viewfinder. Focusing at 20 feet appears to actually be infinity, and at 50 feet, nothing is really in focus, as it is focused beyond infinity.

What seems odd to me is that when I focus at a distance that is indicated on the lens distance scale (7 feet or 15 feet for example), that is right where the split image focus says it is in the viewfinder. In other words, the viewfinder agrees with the lens distance scale, but it is actually focused beyond that point. It's almost like the film plane is in the wrong place.

Any ideas?

Thanks,

Dave

 

[benveniste]

Are you using a 220 or a 120 insert, and do you have a different insert you can try?

 

[Dave in Kansas]

I'm using a 120 insert and it's the only one I have.

Dave

 

[brucemuir]

This does seem like a slightly odd issue.
Usually I'd first suspect the focus screen calibration but from the details it may not be.

I know the lens mount on Nikons can be shimmed to proper register with the film plane.
Maybe the lens mount got damaged at some point and is out of calibration/register? ? ?

 

[benveniste]

While it's a little more common on the 220 inserts, check the pressure plate on the insert to see if it's operating correctly. It doesn't sound like a focus screen issue to me, but ensuring that it's seated correctly is also worth checking.

 

[Dave in Kansas]

The pressure plate feels good and springs appear to be doing their job. The lens focuses smoothly with no tight spots, and the lens mount looks new. I'm wondering if the camera could have been dropped and landed on the lens and pushed the moveable element in a slight distance. Or would that show up in the viewfinder focusing?

Dave

 

[ic-racer]

It is pretty common in some medium format cameras (like every one I own) for the film to not lie flat on the film plane (thus focusing behind where the focus screen indicates)

 

[Bob-D659]

Well, you can check the following, is the ground glass image agreeing with the split image? Is the diopter adjustment on the eyepiece set correctly? Also is the focusing screen seated. All can cause similar problems to what you have.