Grafmatic issues with Critical Focusing

[JChrome]

I've been searching for more information on this subject, so if this is common knowledge or if there's a thread about this please feel free to shoot it over.

The issue as I see it is that the depth of the film in the holder is different (1mm difference) between the plastic lisco holders and the grafmatic. That directly translates to the focal plane.



Note: I'm aware that in the above shot, the plastic holder still has the dark slide which is about 1mm. But it's still not the same as the film plane depth as the grafmatic.

I believe my ground glass is in parity with the plastic holders (have yet to test the grafmatics).

Here are some threads that touch upon the subject but don't hit it as directly I think. Has anyone found that critical focusing is impacted by their grafmatic?

http://www.largeformatphotography.in...-to-film-plane

http://www.largeformatphotography.in...hp/t-6315.html

[Alan9940]

I have 4 1268's that I use fairly regularly with a few different B&W films, and I've used them in two different cameras. Never noticed any sharpness issues with my negs. I use both Lisco II and Fidelity Elite plastics holders. So, you've actually measured the depth between the two with a depth micrometer and that's how you arrived at the 1mm difference? Just curious...

[mdarnton]

When you load a sheet of film in the ready position, it fits in front of the dark slide, not behind as with a normal holder. It's not clear if you're measuring with a sheet in the ready position?

There shouldn't be a difference, and Grafmatics are known to be especially good regarding film positioning and flattness, so I suspect something is wrong with either your holder or your measurements.

[Michael Rosenberg]

Well, there is a difference between Grafmatics and Lisco type holders. And there are differences between different manufacturers of double sheet holders. Howard Bond published an article in PhotoTechniques in the late '90s of the differences. I think he stated that Grafmatics were closer to the standard depth. I measured my Grafmatics and found greater consistency and spot on to the standard.

In reality, it probably does not make that big a difference. Get a depth gauge and measure the differences.

Mike

[Kevin Crisp]

I thought somebody did a study on how far various holders were off from the ANSI standard and as I recall the Grafmatic was the surprising winner for accuracy.

Personally, I more often use mine handheld, and by necessity with a wider aperture since I have to get the shutter speed up to something I can hold still for. Nonetheless I've never had any problem with the plane of focus.

[JChrome]

I have 4 1268's that I use fairly regularly with a few different B&W films, and I've used them in two different cameras. Never noticed any sharpness issues with my negs. I use both Lisco II and Fidelity Elite plastics holders. So, you've actually measured the depth between the two with a depth micrometer and that's how you arrived at the 1mm difference? Just curious...

I didn't use a depth gauge but I did use a micrometer and added some measurable spaces together. I'll look into getting a depth gauge. I'm building a camera to take grafmatics and was thinking I would need to change the distance to the lens if I switched between grafmatics/horseman612/lisco

[Alan9940]

I didn't use a depth gauge but I did use a micrometer and added some measurable spaces together. I'll look into getting a depth gauge. I'm building a camera to take grafmatics and was thinking I would need to change the distance to the lens if I switched between grafmatics/horseman612/lisco

If I was building a camera, I would highly recommend obtaining the proper measurement tool to determine how the back needs to be built for proper focal plane positioning.