Making a Ground Glass Focus Screen

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

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 :D

Ian

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 ?

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

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. :)

I just made two 5x7 ground glass focusing screens using this glass: http://howardglassco.thomasnet.com/v...s-2?&forward=1

It took about 10 minutes using a 5 micron powder.

The glass doesn't have any green cast when looking through the edge.

chris

Hello Ian:I just finished your article on making a new ground glass.Excellent work.I noticed in the final image of the finished product that the corners are clipped.Is this specific to the camera it is used on or is it standard practice?.

Thanks,

Doug:)

That was some-one else's GG ground finer & also brighter :) No names of who'd just made it . . . . . . .

Clipped corners are usually added so you can check lens coverage, the idea is that you look through the gap and can see through the lens to see it's not vignetting.

I use both, I have at least 15 LF cameras.

Ian

Does bead blasting or sand blasting work?

I to was just thinking about bead blasting also alanrockwood. We have one at work with fine silica powder. Most times when blasting metal from a distance of 2½"-70mm. I think with glass it would have to be farther back to get an even spread. Plus you will need to factor in the nozzle of the blaster. Grinding by hand with a paste will give lots more control of the finish product. So I believe hand grinding will be better.