Graflok focus problem - HELP!!!

[Scott --]

Hey, all -

Ok, so I took a couple test shots with the new Graflock 4x5 reducing back. Came out like this:


Hmm. That ain't right. Better check the measurements...

Alright, so I measure from an arbitrary point (the inside surface of the back) to the ground glass and, with 4x5 holder in place, to the film plane in the holder.

Hmm. That ain't right, either...

The two distances differ by about 1/4". Now, I had it in my head that Grafloks set the distance between the film plane and the ground glass to be equal, thus making it easier to use one for a cobbled reducing back. The Graflok is one I picked up used; the insert and ground glass are off of my Super Speed Graphic.

Anyone have an idea why I'm not getting agreement between the two focusing planes? Is there a way to adjust ground glass height on a Graflok back? Or is the insert I have specific to my Super Speed, necessitating another purchase?

Thanks for any help.
Scott

[Scott --]

Ok, here's my Graflok setup:




Here's a picture of a GG insert I found online:


Is it possible that I have the wrong insert for this frame?

[Sandeha]

I presume you're saying that your glass is 1/4" further from the lens than the film. And if the glass isn't bedding close enough on account of it being from a different back, then ... I'll guess that you need a hacksaw and a grinder. There must be some lip or a pair of lugs that's preventing this glass holder from bedding in as well as the natural glass holder would do.

Those corners in the second pic look suspicious.

Though I guess you'll want to adjust the base, not the SSG part.

[Nick_3536]

Is it me or does the banister side look more in focus then the opposite side?

[Scott --]

Sandeha, that's as far down as the insert goes. I agree, it looks suspect. I'll post some pictures of what the insert looks like on the Super Speed vs. on the second-hand Graflok frame.

Nick, I just checked that on the negative. The plane of sharpest focus is on the stair right behind Braedan. I think this was shot around f/8 or so; in the big version, you can see the loss of sharpness in that banister.

[Nick_3536]

F/8. How close? You couldn't have had much DOF. Maybe you are chasing the wrong problem?

[Scott --]

Probably 6' or 7' away. It's very possible that the body of the camera was a little askew - gears slip every now and then. I'll chase that problem down next. Still, though, there's a quarter inch difference between where the film plane and the ground glass lie. It's not like that on my Super Speed Graphic...

[Donald Qualls]

Many/most Graflok backs originally incorporated a Fresnel panel between the ground glass and the lens; that will change the position of the ground glass, though not by any quarter inch. OTOH, the inserts I've seen sit down inside the Graflok, the same way a film holder would in a spring back, and the one you have clearly doesn't do so. I'd say that's your problem, though I now wonder if the rest of the back you have is actually a Graflok or something else that was misidentified (maybe even a "Graflex" back intended for the wider holders with a groove instead of a rib where they lock to the camera back -- those might well have a different registration distance, also).

BTW, I'd love to find one of those inserts...

[Scott --]

Donald, this one says "Graflex" in big red letters on the underside of the frame. Thought that just identified the manufacturer, but now I'm a little nervous...

[scrichton]

have you tried flipping the glass over? 1/4 inch seems a bit too much.