ACRYLIC GG

[claudius]

LASER ETCHED acrylic GG.
anyone that has practical experience with this ??

i found it on :http://www.bohemastudio.pl/oferta/matowki-do-aparatow/

35 euro for 8x10" and 200 euro for 18x24"
i am building a 18x24" (50x60cm) camera
the guy seems very pro so hopefully the GG is in order,
i will order a 18x24 cm GG as a replacement in my fieldcamera,
if i get postive feed back from You guys.
it is 3mm plate, will that be stable enough, or should i ask for thicker type.
it is not very hot here in Denmark, 25C is quite a hot day.

klaus

 

[Dan Daniel]

I'll jump in even though I do not use a large format camera. I have no experience with laser-etched ground glass. BUT I have worked with acrylic sheet for a few decades.

3mm (1/8 inch) thick acrylic over an 18" or 24" run is NOT stable. It will flex and bend easily. Unless it is solidly held in place on the edges you will get warping and flexing in the middle.

At that size, expansion and contraction will not be huge concerns, but a clamping system rather than screws without clearance would be recommended. I do not know what kind of mounting or framing system is used for the GG on your camera.

http://www.centralsigns.com.au/files/Expansion&ContractionTechNote.pdf
http://www.eplastics.com/Plastic/Plastics_Library/Coefficients-of-Thermal-Expansions-of-Plexiglass

Well, just a reaction to the idea of using an 18 inch run of acrylic as a focusing surface. I'll go away and let people with direct experience of your situation bring some reality to your question...

 

[Andrew O'Neill]

I'll bet it is leaps and bounds better than my hand sanded 1/8" thick acrylic GG on my 14x17 inch camera! It's pretty bright but focussing on fine detail is difficult, due to rough texture.

 

[Steve Smith]

It will probably be o.k. but I would go with 5mm. I have a 3mm acrylic screen for 5x4 but I think it might be too flexible for 8x10.

And now we have a new laser, I'm going to try this again. It wasn't very good with our old machine.


Steve.

 

[Steve Smith]

And now we have a new laser, I'm going to try this again. It wasn't very good with our old machine.

I made a 6x6cm laser etched screen on Friday. It actually worked very well. I'm going to try a 5mm thick 5x4 screen next.


Steve.

 

[claudius]

i just recieved the 18x24 cm GG from the above mentioned.
at first glance and tests it looks very fine with no "splints" reflecting light as often seen on handground glass.
also in the details with loupe it looks fine.
worth all the money.
the seller is very helpsome, i mentioned the expansion in cold and hot weather and he quickly made at test.
from 10 to 40 degree C it only lengthened about one millimeter, not a problem.
i got hold of a sheet of 3 mm plexiclass, not quite 20x24", but it seem stabile enought for me to use.
only problem might be if i press the loupe too hard, and possibly bend the GG a fraction.

i can reccomend laser etched Ground Glass from Bohemiastudio. pl
klaus

 

[DREW WILEY]

The biggest risk of acrylic is that it can bow out of flat. The bigger the size, the more the risk. The physical properties of all these plastics are
well documented. But with regard to this particular issue, it's probably not a good idea just to leave the camera sitting out somewhere with
one side of the GG getting hotter than the other. Keep it shaded with the darkcloth, and the lens cap on, or turned away from the angle of the
sun.

 

[rdg]

Steve,

With you having the ability to etch acrylic have you considered trying to etch glass with your laser?

The laser causes a texture and produces very fine shards of glass. The explanation for the effect that I heard is that small bubbles in the glass expand upon being heated by the laser and burst which causes the glass shards and texture on the surface. The glass does not melt as with the acrylic but there is a perceptible texture from the glass surface being heated. Trying to cut glass with a laser requires going over the same pattern a lot of times and etching into the surface a very small amount each time which really makes it impractical.

I have seen someone try etching glass, in this case normal window glass, with a 40W laser and the results were interesting. It was an experiment and learning experience that was not used again. Doing a 4X5 ground glass is going to take a while as you are going to have to do a lot of lines to have an even coverage.

Richard