New ground glass for my Crown Graflex: how do i install

[photobymike]

I did my due diligence and research on how to install the ground glass in my Graflex Graflock back. There are many varied opinions how to do this. How about how and why?.... i do know the ground portion has to be on the same plane as the film.... but i do not have a micrometer to check .....

so lets see how many ways there are here

thanks in advance

[C. D. Keth]

It should be as simple as removing the old one and putting the new one, ground side toward the lens, in its place. If there were any shims under the glass, leave them in place.

If there wasn't a groundglass there when you got it and you don't have precise measuring tools, you can install the new one and shoot a yardstick laid out on a table. Use a wide lens and shoot wide open, taking note of what mark on the ruler you focused on. When you inspect the negative, that should tell you if it's on or needs adjustment.

[photobymike]

mmm well i removed the old one by dropping.... lots of pieces .... yea will shot the yard stick, but there must be a way ground out or in.... a friend of mine say use a piece of 1mm plastic in front of the ground ... i would think this would be strange but his is like this.....

[Jon Shiu]

There is normally a fresnel under the ground glass, which moves the ground glass back some. So, if you have no fresnel, you would have to measure and shim your screen to match the film holders.

Jon

[photobymike]

yea thats what i thought ..oh crap i need to find a fresnel lens.....thanks jon

[Kuzano]

I did my due diligence and research on how to install the ground glass in my Graflex Graflock back. There are many varied opinions how to do this. How about how and why?.... i do know the ground portion has to be on the same plane as the film.... but i do not have a micrometer to check .....

so lets see how many ways there are here

thanks in advance

If you are in a community of any size, there should be a tool rental shop that rents micrometers, particularly a depth gauge.

You could do a work around. Take a piece of aluminum or steel plate that spans the 4 inch width of your film holder. Span the film holder opening. The take another piece of narrow place and set alongside the span plate and down against the film plane in the holder. Use a couple of small C-clamps to secure this. Another option is to drill two hole after clamping and rivetting the two plates together for a permanant tool.

I normally do this with a piece of exposed film mounted in the holder. When the second plate is attached firmly to the first plate, you now have a depth gauge that can be used to:

1) determine the exact placement of the ground side of your ground glass with regard to depth.

And:

2) check all your film holders for consistent same depth. Keep this for a check on new film holders acquired.

Properly placing the ground glass surface in the camera is only half the battle if you get film holders that vary in depth. Your next out of focus image could be traced to an odd film holder, in which all your work to place the GG surface properly would be for naught. (I always wanted to create a sentence in which the term "for naught" would be appropriate.)

[Bill_1856]

Early Speed/Crown Graphics came without any Fresnel. If yours didn't have it then you just replace the GG without any shimming (rough side toward the lens).

[IanG]

There is normally a fresnel under the ground glass, which moves the ground glass back some. So, if you have no fresnel, you would have to measure and shim your screen to match the film holders.

Jon

Unfortunately it's not always the case some (graflok as well) backs came with a fresnel and some without and the casting numbers are the same. So as others have said it's worth checking the register with the new screen fitted.

Ian

[Jon Shiu]

Yes Ian is correct, do install your screen and check if it's in the correct place. It's easy and will take 5 minutes: first remove the graflok back and install the ground glass, frosted side towards lens. Then make a depth gauge from a pencil and a toothpick/matchstick, fastened on with a rubber band. Put the pencil across the back of the back and push the toothpick against the ground glass. Next, take a film holder and with the slide out, put the pencil across the width and see if the depth matches.
*one of our esteemed members wrote how to do this in View Camera Magazine.

Jon

[cowanw]

I am thinking that if you dissassembled the old GG with gravity, it would have been pretty obvious if there was a piece of plastic left in the back of the camera. I expect younever had a fresnel to start with.

[IanG]

I am thinking that if you dissassembled the old GG with gravity, it would have been pretty obvious if there was a piece of plastic left in the back of the camera. I expect younever had a fresnel to start with.

You'd be surprised how many backs have missing fresnels, I've two Graflex backs that came without - one on a Super Graphic.

It's a 2mm differance so it's easy to tell using the method Jon Shiu's mentions.

Ian

[photobymike]

You'd be surprised how many backs have missing fresnels, I've two Graflex backs that came without - one on a Super Graphic.

It's a 2mm differance so it's easy to tell using the method Jon Shiu's mentions.

Ian

Yea i just bought one.. It makes a big difference in focus. I dropped the back and glass all over with no fresnel screen. I spent the whole day researching this question. I need a micrometer to check this

[ruckusman]

If you don't have a micrometer, in this case a depth Micrometer, then the film is exactly 3/16" or 4.74mm from the outside face of the holder.
So the ground glass should be recessed by precisely the same amount

One easy way to have something this thick would be a 3/16' drill bit, but if you have a hobby store close by they may have brass and aluminium square bar stock in 12" or so lengths.

The stuff we have over here in OZ is all imperial and 3/16" is common and plentiful

They will also likely have packs of shim brass in sheets which you can cut with a pair of scissors to make any adjustments.

peace out

Glenn

[Jim Jones]

According to the 1951 ASA specifications, the distance from the face of a 4x5 holder to the face of the septum (the "T" distance) is 0.197 +/- 0.007 inches. The slot that holds the film is 0.012 inches. Much film is about 0.007 thick. Therefore the film can be from 0.197 to 0.178 inches from the face of the holder and be within specifications if my rusty math works right at this time of night. As Glenn suggests, a 3/16 bit falls exactly in the middle of that range. The measurement from ground glass to it's frame face should be made from a part of the frame that actually contacts the same surface that the film holder contacts. On a Graflok frame, part of the front surface of the frame is set back from the surface at the corners.