The choice of ground glass material for DIY project.

D

Dreamish

Member
I used to use the Canon EE-S focusing screen as the ground glass. But it exhibit problems like weird bokeh and ghosting effect. But the lightloss and sharpness is fine.

I'm planning to grind the ground glass myself. People said grinding the ground glass with 12micro Alumiumium Oxide can produce good result. How does the hand grind GG compared to the canon focusing screen?
 
I read about a company called satinsnowglass a while back. They make gg's to order. I think they have a huge back log, but it seemed interesting. They use some sandblasting technique that is supposed to produce much finer grit on the gg....

Jason
 
j,

You have any lying around you want to get rid of or sell? I've been using Light Shaping Diffuser screens and want to try something else.

-rh
 
Dreamish said:
I used to use the Canon EE-S focusing screen as the ground glass. But it exhibit problems like weird bokeh and ghosting effect. But the lightloss and sharpness is fine.

I'm planning to grind the ground glass myself. People said grinding the ground glass with 12micro Alumiumium Oxide can produce good result. How does the hand grind GG compared to the canon focusing screen?
Click to expand...

You might have already read this, but I was very happy with the results that I was getting with the 12 micron aluminum oxide:

http://snodart.com/hbe_snod35_v1_6.php

I wasn't happy with the Canon screens for the same reasons that you mentioned.

5 micron aluminum oxide will look great when the 35mm lens is open, but around f/5.6 (on a 50mm lens for example) the screen won't be able to diffuse the light properly and you will get a hot spot (which gets worse as the aperture gets smaller).

5 micron aluminum oxide at f/22:
hotspot.jpg


This footage below was shot with a GG that was ground with 5 micron aluminum oxide. Worked great, but I never opened the lens past f/4. Anything above f/5.6 would have started to look like the image above (worsening as the aperture size decreased).

5 micron footage

I found that 25 micron aluminum oxide left too many large chips in the glass that even vibrating or rotating wouldn't hide.

500 silicon carbide will give pretty good results. It will create a surface that is somewhere between the 12 micron aluminum oxide and the 25 micron aluminum oxide. The Nikon D screen ends up somewhere between 12 micron aluminum oxide and 500 silicon carbide (in terms of the texture of the surface).

I tried and tried to get a hold of satinsnowglass, but eventually gave up. I think he is a little overrun with email and orders. Might be worth trying some more though.

I did have some luck with making wax screens (daniel's tutorial). These takes some trial and error to find the correct thickness and mixture of wax, but once you figure it out then it isn't so hard to make them. The microscope slide glass that I used to make the screens did create a funky linear flare though. I'm sure you could get some thin coated glass from Edmond Optics that would correct this problem.

So, long story short.... the 12 micron is my favorite and is what we used to shoot The Seeing and After Class. I honestly can't remember if we used a Nikon D screen or a 12 micron aluminum oxide screen for Cache.

Hope that helps.
 
Sno,

Do you have a 5mm and or 12mm glass lying around? I'd like to try it out on my adapter sometime. I ordered one off of ebay but the glass broke in the mail.
 
j is correct.

I don't think I have any extras around. Sorry.

The glass from a UV filter will work great. You can get a nice glass cutter at the hardware store and cut to shape if needed. The glass is normally pretty thin and will break easily, so cut and grind with care.

Grinding isn't as hard as it might seem. You can get some lapping powder (aluminum oxide) and a few UV filters and knock out some nice GG's. One thing that I have noticed about the glass that I grind myself is that it does not scratch as easily as other pre-made focusing screens (D screen, beattie, etc). I have cleaned mine with Windex and a soft cotton cloth before with no problems (you will have to brush away the tiny fibers after the glass dries). And if you do scratch or smudge one.... you can always grind it again.
 
yeah, bit of a typo on my end. i knew it wasn't mm. well i'm not going through the hassle of having to buy glass and grind it. it takes at least few try's to get it right and i'd rather just find someone willing to either sell them ground already or have one lying around.

-rh
 
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