Making a Ground Glass Focus Screen

Ian Grant · Jun 24, 2010

Ian Grant submitted a new resource:

(there was a url link here which no longer exists) - Making a Ground Glass Focus Screen

This is a relatively simple task and the requirements are minimal.
The blank glass cut to size (2mm thick is ideal)
A sheet of Wet & Dry #200 to #400 grit
The grinding grit (one or two grades) #400 & #600 Silicon Carbide
A piece of glass as the grinding tool (blank) approx 2"x2" to 3"x3" (5x5 to 7.5x7.5 cm)
(I use 1/4" - 6mm thick glass as the grinding blank as it's easy to handle.)

SAFETY...

(there was a url link here which no longer exists)

doughowk · Jun 24, 2010

Very good article. Thanks Ian. Now just need to find a silicon carbide supplier.

Christopher Walrath · Jun 24, 2010

Ian, have you ever used automotive grade valve lapping compound and do you know of its effectiveness, pros, cons?

David Grenet · Jun 24, 2010

Thanks Ian - I'll have to have a go at this for my Speed Graphic!

Have you tried doing two at once instead of using a separate grinding piece? As you say, modern glass is very flat so the reason given in 1898 for not doing it shouldn't stand any more...

cowanw · Jun 24, 2010

David Grenet said:
Thanks Ian - I'll have to have a go at this for my Speed Graphic!

Have you tried doing two at once instead of using a separate grinding piece? As you say, modern glass is very flat so the reason given in 1898 for not doing it shouldn't stand any more...

I thought that too but it does not work so well, principlely because it is difficult to get all parts of the GG surface grinding equally. You will need to concentrate on a few areas where your random movements are not so random usually the corners. To get the corners of two gg's going together is hard and you will end up doing an uneven job on one or both.
Regards
Bill

cowanw · Jun 24, 2010

Christopher Walrath said:
Ian, have you ever used automotive grade valve lapping compound and do you know of its effectiveness, pros, cons?

Automotive compond is coarser and faster. The coarser the grind the brighter the image but the more a center spot dominates.
Regards
Bill

Ian Grant · Jun 25, 2010

Christopher Walrath said:
Ian, have you ever used automotive grade valve lapping compound and do you know of its effectiveness, pros, cons?

Yes, I've used fine lapping paste in the past to make a temporary screen, but it's to coarse, it's not really any faster than using #400 grit either. It takes more cleaning off after as well.

David Grenet said:
Have you tried doing two at once instead of using a separate grinding piece? As you say, modern glass is very flat so the reason given in 1898 for not doing it shouldn't stand any more...

You can grind 2 smaller screens together, I've done it but it's not as easy to maintain even pressure etc while you're grinding - there's too large a grinding area, also more difficult as it's harder to hold, this is where a smaller 1/4" - 6mm thick piece of glass really comes into it's own, even with larger screens.

doughowk said:
Very good article. Thanks Ian. Now just need to find a silicon carbide supplier.

You might try here they should stock grit, if not they'll certainly tell you who does

Gem Lapidary Jewelers
Gem Lapidary Equipment Inc*
4206 Herschel St
Jacksonville, FL
32210-2208

Ian

david_mizen · Jun 26, 2010

ive used fine automotive grinding paste - no problems my set up is to place a layer of news paper on a true flat surface and keep a bucket of warm water with detergent in it to one side to do the wash downs with and wipe down at the end with alcohol at the end to remove any residual oil from the grinding paste

DCM

david_mizen · Jun 26, 2010

for those looking for silicon carbide try those dealing in amateure telescope making they usually have supplies of the stuff.

Ian Grant · Jun 26, 2010

david_mizen said:
for those looking for silicon carbide try those dealing in amateure telescope making they usually have supplies of the stuff.

Lapidiary suppliers (stone polishing) are rather more common and carry Silicon Carbide, as do some jewellery suppliers.

Ian

nick mulder · Jun 26, 2010

I might give this method a try - last one was acid etched, seemed simple enough and I didn't lose an eye - the method you outline seems possibly a bit more earth friendly however ...

I was thinking of grinding/etching some museum glass one day (or the cheaper AR Reflection-Free®)- might be a bit of extra work getting through the coating properly but I thought that at least with one side still coated with less reflection that maybe a GG could be used sans dark cloth in a few more situations than normally ... Your thoughts ?

Ian Grant · Jun 26, 2010

The coating shouldn't make any difference to the grinding, it might be an advantage having one side coated, but I'm not having a problem with my Quarterb plate camera with a plain uncoated screen, but I wish my fresnel on the Crown Graphic was coated. I guess I could coat it with the anti-reflective spray sold for studio use.

Ian

Q.G. · Jun 26, 2010

Ian Grant said:
[...] I wish my fresnel on the Crown Graphic was coated. I guess I could coat it with the anti-reflective spray sold for studio use.

Dulling spray?
You could. But you wouldn't see anything through if you did.

But i guess i swallowed that hook, line and sinker.

Ian Grant · Jun 26, 2010

It's translucent, you can see through it with no problems, it's used to kill reflections when photographing objects with highly reflective surfaces but it's not durable.

You only need to spray a very light dust coating to kill most of the reflections, I guess clear acrylic lacquer air-brushed on very finely would work well, but I wouldn't want to ruin the fresnel screen trying.

Ian

Q.G. · Jun 26, 2010

Yes, i know the stuff.
But it would be just like you would have a layer of condensation on the Fresnel, not good for seeing through.

But perhaps we can use it to create a temporary ground glass screen?

Ian Grant · Jun 26, 2010

nick mulder said:
I thought that at least with one side still coated with less reflection that maybe a GG could be used sans dark cloth in a few more situations than normally ... Your thoughts ?

Quite a few APUG members could tell you that mostly I work without a dark-cloth although it's always in the back pack, that's with 5x4 & 10x8. But the Graflex screen was so dismal and even with the screen hood it was near impossible at times, adding a fresnel made a huge difference but was still not close to my Wista or Cambo. With a freshly ground screen I'm on a par with the Wista at last, it's not the same the Wista has more contrast (I have the integral screen/fresnel) but surprisingly it allows very much finer focussing, and it's easy.

I've been using one here in Turkey, and there's a lot of light today and these screen are a real joy to use, but the weather's been unusually poor during the week (this time of year we expect sun and a perfect blue sky Dawn to Dusk) and even under heavily overcast skies & lowish light levels the screens are so easy to use.

Keep planning on making a simple focus screen shield from offcuts from my bellows making for my Wista, & Quarter plate camera because I find the Crown Graphic focus hood is a great solution. |should be making this in the next few days. If it works I'll post a pattern etc.

Ian

Q.G. · Jun 26, 2010

I forgot before: thank you, Ian, for this brilliant "how to".
Makes me want to have a go, even though i don't need a focussing screen. So now i'm trying to think of things i could do once i made a screen myself.

PVia · Jun 27, 2010

Can you use this method to make a quasi-ANR neg carrier top glass?

bobwysiwyg · Jun 27, 2010

Is there any advantage to going finer than #600 grit, or is it a matter of diminishing returns beyond that?

Ian Grant · Jun 28, 2010

bobwysiwyg said:
Is there any advantage to going finer than #600 grit, or is it a matter of diminishing returns beyond that?

Yes you can go finer, but it's the balance of contrast/brightness and fineness that makes the difference.

There may be some variations in Grit quality but using #400 followed by #600 gives screens that are superior to the standard Graflex screens and many other commercial screens.

PVia said:
Can you use this method to make a quasi-ANR neg carrier top glass?

No because the grain of the ground glass will be an issue.

Ian

c.louis · Jun 30, 2010

Would it be difficult to make one for Hasselblad 500C? My focus screen is so dull and gray.

Ian Grant · Jun 30, 2010

Possibly not, but you'd need to grind a very much finer screen.

It's far better to get the correct screen, with MF focus is far more critical. You could give it a clean - carefully

Ian

removed account4 · Jul 2, 2010

great article ian!

could this be done with plexiglass
so ultra light camper hiker types
won't have to worry about breakage
or is the thickness of the plexi and issue ?

Ian Grant · Jul 2, 2010

Plexiglass/Acrylic

I made an plastic screen just before coming back to Turkey, not 100% sure it might have been acrylic, but it works just as well. There's plenty of materials the right thickness, used for leaflet dispensers etc, it's finding the best one, and getting small pieces.

So yes it can be done with a very big proviso, it'll mark, scratch etc, very easily while you grind it if you catch it with the grinding blank. Ideally you need to work off all the edges and corners of your grinding blank until all edges are well rounded.

Then you'll find the screen surface may not be perfectly flat like modern glass, so you have to grind and work off any hot spots, then when flat wash well & use finer grinding paste.

It's better to use a different grinding blank for each grit size, especially with plastics/acrylics because each grinding blank itself gets a ground surface and a coarse blank with fine grit can undo the finer grinding work if your not careful.

adding: Should have thought of this before, the grinding blank ideally should be the same material and not glass, if glass is used you run a risk that the grit while grinding the acrylic is also grinding the glass blank and the glass particles cause problems.

Ian

totalamateur · Jul 12, 2010

Rock tumbler grit works well for grit, as it is usually silicon carbide. The grit I used was a little coarse, which has cause minor focusing issues, as the grain in the glass can be quite large, though it is much brighter than the "factory" glass.

One tip, I prefer to grind the glass before cutting, as this reduces the problem of un even grinding in the corners. For a 4x5 screen, I start with about 6 x 7 or 8, and then cut down. Cutting glass is quite easy once you get the hang of it, and it's a $9 tool and a bottle of baby oil.

The bottom of a beer bottle works well as a grinding tool, and has a familiar grip to it.

Making a Ground Glass Focus Screen

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