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Old May 11th, 2005, 12:10 PM   #1
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Mini35 groud glass

I've just had an idea, maybe someone had it before, and maybe it won't work...
I'm quite new in video, but I do SLR photography for a while.

In SLR cameras, the viewfinder is based on a mirror that projects the picture on a ground glass behind the lens you put your eye on.

These ground glasses are very good, with a very very thin grain (Laser etched) and a very good luminosity.

One could be found on a defective ready-to-be-trashed camera.
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Old May 11th, 2005, 02:01 PM   #2
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Welcome to this forum Etienne,
I have been using it since July 2004. Is the best choice (imo).
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Old May 11th, 2005, 02:06 PM   #3
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Etienne,

Yes, these focusing screens are being used by some as a ground glass, with good results. However, getting one the proper size to fit in a tube has required buying larger focusing screens and cutting or grinding them down to the proper dimension. The high quality screens can be very expensive, a few hundred dollars. Results look good though.

Other ground glass options include optical ground glass, fresnels screens designed for other purposes, micro-crystaline and other wax techniques. Lots of options.

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Old May 11th, 2005, 02:26 PM   #4
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I also thought of a regular glass piece, with one face dipped a few seconds into some strong acid (HF works, but something less dangerous could also work). This gives a white transluecent smooth surface.
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Old May 11th, 2005, 02:46 PM   #5
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http://www.poc.com/lsd/default.asp
This company manufactures some of the finest (if not the finest) diffusers I have come across and tested. They might save you the trouble with "home made" glass etched.
Two problems though:light loss of almost three stops and the hot spot associated with any diffusing surface (distance from the lens to centre of the GG is smaller than lens to corners. (Light's sq. law fall off with distance applies) Although almost undetectable for film (as in still or MP), the CCD's limited contrast ratio makes it obvious in this situation. Solution: a medium to disperse the light towards corners and "even out" the big brightness diff : a focusing screen. (If anything else was better, Nikon, Canon etc would have used it for many years by now, I think).
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Old May 11th, 2005, 02:58 PM   #6
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I tried many ways of etching acryl or plexy glass without good results. That's because the structure of the plastic becomes visible I think.
Etching quality glass would be something I'd be very interested in.
When you are talking about the GG of a ready-to-be-trashed camera, don't forget that many camera's have a focus circle in the middle.
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Old May 11th, 2005, 03:13 PM   #7
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Looks like "hobby" is what you are after... Take a color reversal film (medium format or SLR) and photograph an even lit surface. Do not focus on the surface! (all you want is an even medium of fine resolution, right?). Lowest ASA (or DIN) and skip bleach. That will leave all the silver in the emulsion. Fix and dry. Smoothest grain, smoothest diffuser. Have fun.
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Old May 11th, 2005, 04:25 PM   #8
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Dan, I read something like what you describe with the reversal film somewhere on the board. Sounds good, but static grain, right? That's what you mean with hobby? Hobby grain sounds like fun. I'd need to vibrate it for good results though, because I'll put my two camera's on it again for a 720i resolution.
But isn't this a technique that can be refined to high quality results?


..One question, why color reversal? Why not just B/W reversal?
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Old May 11th, 2005, 05:59 PM   #9
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Oscar,
I walk my talk. Had I believed in static solutions, I would have done something in that respect, right? Well,.. I do not, and please, no offence to other "religions".
Film has grain. Right? If we were to blow up an 18/24mm FILM FRAME to a theatre size screen, you would see the grain in its whole splendor. The reason we do not see the individual grains (while watching a movie) is because they never show twice in the same spot (go-damn-it) there are too many to count ;-)< and the persistence of vision fills in the gap!
Although some of the finest diffusers I have tested (POC) would allow one to "get away with" (to a certain extent), the SOFT areas will show it.(I have some night pics on my site to support the argument).
long story short: static is hobby (IMO) sorry again, no hard feelings for other believers. If and when anyone will get a good image on a 50" monitor from a static "GG" (while panning the camera) please let me know (seriously! and no pun intended)

Why color reversal? Just a guts feeling.... ;-)< but don't take my word. Try them both.

Last edited by Dan Diaconu; May 11th, 2005 at 06:44 PM.
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Old May 11th, 2005, 06:11 PM   #10
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Dan, I trust your opinion on this, so I think I need to put my mind on vibrating or oscillating.
Anyway, I'll try this anyway to get a new GG for my MF Rolleicord. The original one is messed up and I can't take a decent picture with it.
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Old May 11th, 2005, 06:46 PM   #11
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Do your "homework" on WHAT YOU HAVE!!!!!!!!!!!!!!!!!!!!!!
When you are READY and THERE ;-) get the real stuff (you will know what to do with it!) but only THEN!
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