Ground Glass Modification

aaronmichael · Feb 11, 2012

Hello All,

Picked myself up a 1960's Crown Graphic 4x5 a couple weeks ago and I love it. Unfortunately the ground glass doesn't have any composition marks or a grid on it. Makes it a little difficult when trying to get straight horizon lines, building lines,...etc. Rather than spending $35 on a new piece of ground glass, I was wondering if I could save my money and just draw my own marks on the current ground glass with a super fine tip sharpie or something similar. Or should I not ruin a good piece of vintage ground glass and just spend the $35 + shipping? Any advice/tips would be greatly appreciated!

Existing Light · Feb 11, 2012

if you can find a sharpie (or other marker) fine-tipped enough, I'd say go for it. Just be sure you get the lines just right the first time because permanent marker is a biotch to clean off glass

And if you totally screw it up, you can always buy a new one then

I wouldnt be worried too much about a "vintage" focusing screen. I mean, it's a piece of glass. but then again, having all original pieces might actually mean something to you

dehk · Feb 11, 2012

Draw on the smooth side (non grounded side) so you can wipe if off anytime in the future.
Whichever way you are going to do it (on camera, or take it off and do it somewhere else), be careful not to scratch the grounded side.

aaronmichael · Feb 11, 2012

Thanks for the quick replies and good advice. I'm a newbie to large format - which side is the grounded side? The side that faces you or the other side?

Ian Grant · Feb 11, 2012

The ground side is the matt side and facing the lens. It's best to draw on this side, I marked up a screen in 1976 using sharpened Chinagraph pencils and it was still ok when I sold the camera last year.

Your Crown Graphic may have a fresnel in which case that will be between the glass screen and the lens in th focus frame. It's probably worth replacing the screen anyway as the Graflex screens are not very bright. The other alternative is to regrind the surface which is quite simple and quick - I've done both. I've found this gives approx 2 stops better brightness which makes focussing very much easier.

Ian

aaronmichael · Feb 11, 2012

Would you recommend using a grease pencil rather than something like a sharpie?

Steve Hamley · Feb 11, 2012

The finest sharpie you can find on the non-ground side.

Cheers, Steve

keithwms · Feb 11, 2012

I use very light pencil marks on the ground side.

M. Lointain · Feb 11, 2012

I say either pencil on the ground side or a fine sharpie on the smooth side. If you just want to be able to level horizons then just put a series of marks on the edge. You can keep the center clear that way.

I dramatically improved my Speed Graphic ground glass by waxing it. It is incredibly bright now. It made a huge difference even though it already had the fresnel.

dehk · Feb 12, 2012

Reason I say do it on the smooth side first is to practice before you ruin a good screen.

Ian Grant · Feb 12, 2012

There's another alternative which I've used as well and that't to print a grid onto Transparent OHP material, the Laser print material works best but if you only have access to an Inkjet printer it's still worth a try. The printed side goes against the glass.

You need to decide whether to use a metric or imperial grid, I prefer a ½" grid for a 5x4 camera and a 1" grid on a 10x8.

Ian

resummerfield · Feb 12, 2012

I would use a hard pencil, like a #3, and lightly mark on the ground side.

aaronmichael · Feb 12, 2012

I think I got talked into making my own, using Ian Grant's method - but using the valve grinding compound instead of silicon carbide.

Ian Grant · Feb 12, 2012

aaronmichael said:
I think I got talked into making my own, using Ian Grant's method - but using the valve grinding compound instead of silicon carbide.

As I just posted on your other thread Valve grinding paste gives a poor quality coarse finish, ask in a local Lapidary suppliers or shop, there's 13 listed for Long Beach in the yellow pages

Do it properly with Silicon Carbide, you don't need much at all - a 35mm film can full will do quite a few screens and a stone polisher might just give you some #400 and #600 grit for free.

Ian

aaronmichael · Feb 16, 2012

Ian Grant said:
As I just posted on your other thread Valve grinding paste gives a poor quality coarse finish, ask in a local Lapidary suppliers or shop, there's 13 listed for Long Beach in the yellow pages

Do it properly with Silicon Carbide, you don't need much at all - a 35mm film can full will do quite a few screens and a stone polisher might just give you some #400 and #600 grit for free.

Ian

After calling multiple places I finally was able to find the Silicone Carbide - so that's good news. Now the problem is that I'm having trouble finding the right kind of glass. It seems that it's quite difficult to find glass as thin as the one in Crown Graphic these days? I talked to a lady at a glass shop and she said that even if I could find a piece of glass that thin, after grinding it, the piece of glass would be uneven in spots. However, I didn't tell her what method I was going to use so maybe she thought I was going to do something different. I suppose my main question now is: Does the thickness of glass matter that much when making a new screen? Obviously it can't be took thick. But would changing the thickness of the glass affect focusing? Would something like this just from home depot work?

http://www.homedepot.com/h_d1/N-5yc1v/R-202091046/h_d2/ProductDisplay?catalogId=10053&langId=-1&keyword=glass&storeId=10051

Any additional information would be great, thanks!

Mark Crabtree · Feb 16, 2012

The image focuses on the ground side, so thickness doesn't really matter there, but somewhat thinner than window glass is nice for good fit. I don't think you are really going to have problems with uneven spots.

John Austin · Feb 16, 2012

Firstly make a accurate drawing of the lines you wish to draw on your screen, then lay the GGS on this and mark with a sharp pencil on the ground side

Pencil can easily be removed from the GGS by washing

However, given that you can get a marked GGS for $35 I can't understand why you don't just buy one and use your existing screen as a spare - I would never go on a job without a spare GGS and a tiny tool kit, even with a Speed Graphic focusing screen flip-out metal viewing shade thingie as a GGS protector for my 5x4" Sinar and the Linhof already has one - A spare GGS is much cheaper than embarrassment, fuel, model costs, location rent and even film - Now I am retired I still carry a spare GGS and tool kit

(I hope I don't become a grumpy old man in my retirement)

Sethasaurus · Feb 16, 2012

If you need thinner glass, keep an eye out for cheap picture frames.
We have them here in dollar stores and a lot of department stores and they're fairly inexpensive.
Often they around 1-2mm and are also pretty close to the size you need - you may have to trim one side, for example.

Ian Grant · Feb 17, 2012

2mm glass is fine, that's what most suppliers of Ground glass screens use these days. Thinner glass isn't sold to the public in most places any more on safety grounds as it's more prone to beakage. 2mm fit's a Crown Graphic with no problems. I've made well over a 100 screens nowusing 2mm and it'll fit the vast majority of focus frames, I've only had problems with two old pre-WWII Geraman and British metal plate cameras and this is when I've used old fogged glass plates to make screens.

Picture glass is 2mm and modern glass is very flat so you won't need to grind out hot spots, I occasionally use older glass platesbut it isn't as flat. In most areas Window glass has to be much thicker, even green-house glass has to be 4mm thick now (here in the UK).

Ian

aaronmichael said:
After calling multiple places I finally was able to find the Silicone Carbide - so that's good news. Now the problem is that I'm having trouble finding the right kind of glass. It seems that it's quite difficult to find glass as thin as the one in Crown Graphic these days? I talked to a lady at a glass shop and she said that even if I could find a piece of glass that thin, after grinding it, the piece of glass would be uneven in spots. However, I didn't tell her what method I was going to use so maybe she thought I was going to do something different. I suppose my main question now is: Does the thickness of glass matter that much when making a new screen? Obviously it can't be took thick. But would changing the thickness of the glass affect focusing? Would something like this just from home depot work?

http://www.homedepot.com/h_d1/N-5yc...d=10053&langId=-1&keyword=glass&storeId=10051

Any additional information would be great, thanks!

Ground Glass Modification

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