Making Your Own Ground Glass

This week I and another friend got together and made our own ground

glass following the instructions of Dick Dokas in the May/June 2003

issue of Photo Techniques, and thought I would post it here for

those who would find it interesting.

 

We ordered the 3 and 5 micron grinding powders from Willmann-Bell

(800-825-7827 who were great to work with) and I had the glass cut

to size at a local glass shop.

 

It took us about three hours from start to finish to create two 5X7

and two 8X10 ground glasses, and we were very pleased with the

results. The ground glasses were brighter and MUCH smoother to

focus on than the original 5X7 Deardorff or 8X10 Phillips ground

glass.

 

I made two 4X5 ground glasses for another camera yesterday, and shot

some portraits under strobes with a 240mm f5.6 lense and was very

impressed with the ease of focusing under modeling lights as

compared to the original GG.

 

If you have any questions don't hesitate to ask, however, the

articles instructions were through and easy to follow. The main

advantages you will see is the increased brightness and the ease in

focusing with the loupe because there is little grain and you can

really see the details.

 

-Jerry

Jerry: Thanks for your interesting posting. I compared a Beattie Intenscreen with a Linhof screen of some 20 years ago. Using my Pentax spotmeter the Beattie came up 1/3 stop brighter. Viewed through a 10X loupe the Beattie was very slightly finer. Good for the Beattie but...was it worth its considerably higher price? Have you viewed your home made screens through a high magnification loupe? Are the screens even from side to side? How flat is the glass that you made the screens from? I'd be interested in the info on how to make the screens, is it posted anywhere in the Internet? Thank you.

Julio, you will find the screens to be about a stop brighter than a conventional GG. Through a loupe you will find that the grain is much finer than a conventional GG, and it really is a pleasure to view such a smooth image and see such fine detail. Both my friend and I appreciated the added brightness, however we were both very impressed with the smoothness more than anything else. I might add that a regular GG is made from European glass and we made ours from regular window pane (float glass) which is 50% thicker and much stronger.

 

As far as the flatness we noticed that in the initial grinding stage you could see waves in the glass (uneveness) because window glass is made by pouring molten glass on tin so it has waves that become apparent when you get into the grinding (streaks of non-milky areas), however as you proceed with the 1/4 thick grinding tool (a 3X3 or 4X4 piece of glass) with the 5 micron grit it smooths out the ripples and makes the glass flat.

 

I have not seen anything on the net on how to do it but the article by Dick Dokas (retired photographic and graphic arts teacher and friend and associate of Howard Bond) is excellent and very detailed. We had no problems following the instructions. It was in May/June issue of Photo Techniques. If you have trouble finding the article I can give you the basic information through email off line.

 

Hope this helps!

 

-Jerry

jerry,

a friend of mine did following: he orderd a clear, coplanar dressed and cut to size glass at an optometrist. he putted on the viewers side and along all four small sides an acid-proof coating. the coating is a kind of bitumen-lacquer. after the coating was dry he swayed the gg thru the steam of hydrofluoric acid. the result was... i have no words for that. the best matting i have ever seen. okay, this procedure has some handicaps too. you have no grid lines for architectural applications. but my friend applied the lines later with a small black marker. the main handicap is: you will need two or three gg until you have the result you want. but when you have the result, you will have a gg with the smoothest matting on the market.

HF is dangerous stuff. This is not anything you want to experiment with unless you have access to a properly equipped lab and someone experienced who can supervise the procedure.

Jerry: Thanks again. 'Float glass' is made by pouring the glass melt into mercury and is perfectly flat. As far as I know, it is only available in the thicker sizes, if it were available thinner it would be ideal. One thought that comes to mind is that the greater thickness of the window glass may change the registration. That would depend on the camera. Registration is an extremely important consideration and I would strongly suggest that you measure it. I will look into the article and contact you for the data if I do not find it. If you have questions on registration I will be happy to provide data.

Thanks

I've been meaning to make my own GG. At the moment, I'm using an emergency GG, RustOleum Frosted Glass spray on one side of a sheet of 8x10 window glass. It's a bit dark and very grainy, but functional. How long does the whole process take for grinding window glass (8x10)?

Julio, float glass is done on tin, or at least it used to be- mercury is incredibly toxic when heated and completely unsuited to the task. Float glass is good, but far from perfect. Not that it matters, as the errors are far less than holder-to-glass agreement. Grinding glass is extremely easy. The process tends to create very flat surfaces. I've also etched glass with HF. The result isn't as good as proper grinding, and HF is pretty nasty. An acid burn isn't the only risk there. It does work well if ones goal is to prepare the glass for bonding with epoxies or similar.

Jason, from our experience I would say with a little practice it takes around 45 minutes to complete an 8X10 GG. Also, so far I have had no problems that I can see with registration and I was shooting portraits fairly wide open at about 5 to 6 feet with a 240mm lense on my 4X5.

 

-Jerry

How thick was the glass? Was it anything special?

Robert, it was just plane single pane window glass just a little less than 1/8 of an inch thick. I think it cost me less than $26.00 to have a glass company cut 2-8X10, 2-5X7, and 2-4X5 including clipping the corners and seaming the ends (labor and material). The two grits, 3 micron and 5 micron were $24.00 and I bought enough to probably due 30 8X10 ground glasses (1 lb each).

Thanks sound like the glass I got from the local guy awhile back to use for 35mm contact sheets. He likes selling it to me at what he thinks is a good price and I think it's a good price. Wouldn't surprise me if we both thought we were getting the better of each other-))

I have received requests via email since making this post for a summary of Dick Dokas�s article since the magazine is not available in some countries. So here it goes:

 

Besides the facts mentioned above you need to get a small ¼ inch thick sheet of glass around 4X4 (fits comfortably between your thumb and fingertips) and have it smoothed (seamed) for use as your grinding tool.

 

Do all your grinding on a very flat surface with some newspaper under the glass.

 

Measure about 1/8 teaspoon of the 5-micron powder onto the center of the glass and add the same amount of water and mix with something like a toothpick.

 

Start grinding with your 4X4 glass moving your hand in two-inch circles, while also moving in a large circle around the blank. As the water evaporates the grinding tool will be harder to move (this happens frequently) so just add a little more water (we had a bowl of water at the table and just sprinkled it from our fingers).

 

Less frequently add more grinding powder as the slurry starts to thin in color (less frequently).

 

Every 15 minutes or so carefully run water on the blank to remove the grit, dry it and check for the evenness of your work (noting clearer areas) and start grinding again. You will know when you are done by the uniformly of the white area.

 

Then go to the 3-micron powder and repeat the same procedure (after cleaning and drying the blank and the grinding tool to remove the #5 grit) for about the same length of time to two times longer.

 

Your muscles will be sore but boy what a great ground glass you will have. I am now going to carry a small grinding glass and two vials of the 3 and 5-micron powder with me on my trips so in an emergency I can grind my own glass if the one on my camera brakes.

 

The results are so good with this process that we owe a real thanks to Dick Dokas for sharing his experience in that article. Hope this helps those who cannot get the Photo Techniques magazine.

Conrad: Thanks for the update on floatglass. Do you know what is the minimum thickness it is made in?

 

As for registration, not all cameras have a provision for compensating for GG thickness and using glass of a thickness different from that used by the camera manufacturer will result in a registration error. That would be the case with Technikas III and IV. I do not know about other cameras. I still wonder how flat window glass is? you are right Conrad that filmholders can be off as regards to registration but at the risk of appearing negative, I like to point out that two errors (the glass and the film holder) one good result do not make, ...unless you are so lucky that the errors cancel out otherwise they will add up. (Quite commonly in this forum it is suggested that one error can be ignored because other errors are also likely. On the contrary, the possibility of a second error is reason enough to avoid the first). Also it may be true that the variation in flatness and thickness of window glass is small but would like knowing if anyone has taken measurements on the flatness of window glass or whether manufacturers specify it. A measurement is better than a guess, no? Jerry's method looks simple enough but I have to wonder if all gound glass nowdays is also made by grinding, after all why would anyone bother with nasty HF? If grinding then is the predominant and possibly the only method in use there would be no excuse for all new commercially sold ground glass screens not to be as good as Jerry's? That said, it is still useful to know how to make a good one so thanks Conrad and Jerry for your postings.

"as for registration, not all cameras have a provision for compensating for GG

thickness and using glass of a thickness different from that used by the camera

manufacturer will result in a registration error."

 

Can you explain? I would have thought that if the ground part of the GG is in the same place as that on the original GG that it doesn't matter how thick the glass is (up to a certain point).

 

I've also had GG's, on older cameras especially, that appear original (or at least are original brand) of varying thickenss from camera to camera. I'm not sure there was ever any standard as to GG thickness? Also, on most older (and some newer) 8x10's and above, the placement of the GG in the back seems a pretty primative affair in many cases.

Has anyone thought of taking their existing ground glass and

grinding it w/the 3 micron grit? I'm most interested in the 1 stop

increase in brightness for wide angle lenses. According to the

article, the commerical glasses were ground w/the 5 micron, not

the 3. Seems like a great approach to upgrade your current

equipment.

Re: "As for registration, not all cameras have a provision for compensating for GG thickness and using glass of a thickness different from that used by the camera manufacturer will result in a registration error."

 

The ground surface of the ground-glass serves to scatter the light rays of the image to the eye or loupe/eye combination. Focusing is done by judging the sharpness of the image as seen with these diverted rays. The diversion takes place at the ground surface -- this is where the image is placed for maximum sharpness. The thickness of the glass behind the ground surface doesn't matter on cameras with the ground surface of the glass facing the lens. The thickness of the ground glass would only matter if a camera where designed to have the ground surface on the back of the glass rather than on the lens side -- I don't know of any cameras with this configuration.

 

As to flatness, I have measured the thicker plate glass and found it to be very flat. If the thinner glass has some microscopic ripples, the grinding process will remove them. Most likely any devations from flatness will be so small that improving the flatness will make negligible improvement to the total accuracy of the system. The main thing to avoid is uneven grinding, e.g., giving more grinding to the corners might make a curved piece of ground glass. The large the plate glass grinding tool is in relation to the intended ground glass, the flatter will be the ground glass.

"David Gabbé , aug 10, 2003; 04:36 p.m.

Has anyone thought of taking their existing ground glass and grinding it w/the 3 micron grit? I'm most interested in the 1 stop increase in brightness for wide angle lenses. According to the article, the commerical glasses were ground w/the 5 micron, not the 3. Seems like a great approach to upgrade your current equipment."

 

I know this thread was last posted to over 4 months ago but I just read it and noticed that noone ever answered Davids question. I'd be interested in knowing if anyone has tried regrinding their existing ground glass using the 3 micro powder. I have a Ansco 8x10 that has a very dim ground glass and would be interested in trying this.

what is the exact name of the 5 and 3 micron powder ?

 

i would like to find some in france but i don't know what is the name

 

christophe - france .

The powder that i have used, which i believe to be the same as the 3&5 micron poweder mentioned above, is silicon carbide powder. Its the powder that lapidarists use (lapidarist are people who polish/engrave stones) and you can buy it in various grades (i used 600 and 1200 grade, 1200 being the finest)from geological shops. I'm not sure about france, but i bought mine from a UK geology suppliers:- http://www.ukge.co.uk/UK/Lapidary.asp

It has worked a treat, and at a low cost.

Hope that helps

James hankey

<p>You can find a link to the original article from Photo Techniques here:<br>

http://www.dokasphotos.com/techniques/ground_glass/</p>

<p>You can obtain the aluminum oxide grinding powder mentioned in the article from Willman Bell. It's available here (scroll down a bit):<br /> <br /> <a href="http://www.willbell.com/ATMSupplies/ATM_Supplies.htm" target="_blank">http://www.willbell.com/ATMSupplies/ATM_Supplies.htm</a></p>