Hiya,
I have been working on the best method for creating my ground glass ready for my spinning glass adapter.

I have tried 1000 grit Aluminium Oxide, but the results have the same problem I had with my optosigma glass, it does not diffuse the light enough, hold the glass up to your eye and you can see through it. Maybe it needs grinding for longer.

I have also been working with acid etching cream. This results in perfect diffusion, but i little too much light loss. But i used a tip i found on this board about applying vaseline to the ground/etched side of the glass and wiping it off again to improve light transmittance. This really works!!! It both brightens up the image and gives it more contrast, without effecting the diffussion.

I have uploaded a test video showing the light loss from my glass. Its just a static microscope slide so you can see the grain of the etching, but this is intended for a spinning glass adapter. Anyhow, download please and comment on its light loss if you would:

http://homepage.ntlworld.com/wayne.kinney/GG.mov

Thanks,
Wayne

Why are you trying to judge your ground glass in a static test when you won't be using it that way? A Mini35 looks like hell when the glass isn't moving.

Have you considered sourcing it from the place Nick Bartleet used?

Bill,
Because the test is to judge the amount of light im loosing from the glass, this will be the same weather the glass is in motion or not. As you can see from the video, the left side of the image is only very slightly darker to the right, the ground glass is loosing very little light, thats what im trying to show.

You can see dust and grain, but this will disappear when the glass is spinning.

Thanks,
Wayne.

1) whether

2) I get it now! Nice work, keep it up. I agree, it's very bright.

Bill,
1)Thanks for my spelling correction;)

2)Thanks, yeah im pretty pleased with the glass. Now to make the spinning glass mechanism:D

Thanks,
Wayne.

Wayne,

Looks great, I love the side by side. It has a nice soft film-look to it, if you can get it spinning or oscillating, that would be great!

Mandy,
Thanks. Im going to spinning it using the method here:
http://www.dvinfo.net/conf/showthread.php?t=49111&page=4

view my last post:D

Thanks,
Wayne

LOL, only kidding about the spelling! :)

I'm lost :) What is receiving the projected image on the right? Or is that aerial as in air? And if it's air, then the left image doesn't seem to be diffusing much. Or is diffusion measured when the camera is focused on close-proximity? I'm on my 20-something-attempt on a wax diffuser, still dealing with dust, stratification, wax type, etc. so maybe I've just got wax on the brain . . . but I've been trying to get the wax to be diffused no matter what the focus setting is. I'm still a newbie at this, but very interested. Thanks for any clarification.
BTW, in the close-up focus portion, I measured a difference of 17% between identical highlights (the book pages at the bottom of the picture). If this works, with only 1/3 stop in lost light, you'll be doing real well!

G

Glen, post your wax trouble on the microcrystalline wax thread, I'll be happy to help.

I'm lost :) What is receiving the projected image on the right? Or is that aerial as in air?

Yes the right is just the aerial image coming straight from the SLR lens, the left is through the ground glass.

And if it's air, then the left image doesn't seem to be diffusing much.

What do you mean not diffusing enough? the left image goes out of focus when i move the lens.

but I've been trying to get the wax to be diffused no matter what the focus setting is.

Not sure if i understand you here. could you explain?

Thanks,
Wayne.

I'm sorry, but I get it now. That is amazing. Do you have an incidence meter? If you do, could you put a short tube over the dome, point it at the opposite-from-the-sun side of the sky and take a reading with it bare and with the ground glass over it? I'm guessing the readings are going to be very close. I can't wait to see what it looks like when you get it moving.
Sorry about my confusion, but I at least learned something ;)

G

Thanks for yor support glen.

I dont have an incidence meter im afriad, so no numerical readings just visual proof as in the video. I guess I could read my camcorders auto exposure reading with and without the glass, pointing at the same shot, but I think it will be the same reading.

Im ordering all my tools and bits next week to make the spinning glass mechanism.

Wish me luck!

Wayne.

Yeah, the camcorder isn't going to be detailed enough -- I was just curious. I think you've really got something here. I'm a little nervous about the spinning glass thing -- for you, that is :) And as to getting the glass cut exactly down the line -- I have reservations about anything mounted to rubber being accurate enough. I have a glass cutter mounted by a metal arm to a stage, and it deviates just by the wobble of the diamond disk. You only get to make one scratch per attempt. Maybe you've already got experience with this -- in which case you can just filter me out of these threads LOL!
But if not, you may want to consider mounting the glass to the motor via a coupler so you can adjust the center of mass after the glass has been cut. This way, you don't have to be perfect in order to move forward with the experiment.
Just trying to help,

G

Another possibility to creating a perfectly balanced glass disk, is to spin it on the motor slow enough (100 rpm perhaps) that any vibration doesn't pose a danger, and use a fine sharpening stone with lots of oil. Mount the motor on something solid, and raise the stone to where it's just barely rubbing the glass. You may be able to grind it to a perfect circle that is perfectly centered on its mount. That would be better than going with a coupling approach.
You may have good luck, and get a perfect cut on a perfect center. I'm just trying to come up with solutions for the off-chance that you experience results more like mine tend to be :)

G

Glen,
Thanks very much for your input. Centring the glass is ofcourse the hardest challenge. Your second sujestion is not far off from my method. I have uploaded 10 diagrams detailing my method on my other thread:

http://www.dvinfo.net/conf/showthread.php?t=50507

But i think your sujestion can be added as a last step to my process. I was thinking of using sandpaper to do the same thing to finish up, but a fine sharpening stone with lots of oil would be much better.

If we can please continue the spinning mechanism discussion on the above thread.

Again, thanks for your input, very helpful.

Wayne.

Wayne, can you explain why this happens? I am wondering why the aerial image cannot function in place of the ground glass. If you were to place the 35mm lens, then an achromat, why couldn't a camcorder record the aerial image off of the achromat without losing the DOF properties of the 35mm lens? I am really curious about this so any help would be great. Also, in your example clip you had the camcorder recording the ground glass directly, right? No other elements were between the camcorder and the ground glass, right? Thanks for your help.

Wow, my old thread, hehehe.

I certainly dont have a degree in optics, but its all down to taget size (size of the senser). Without any GG, the image will be projected directly onto the cams small CCD (through its own lens first, ofcourse). Because of this, there will also be a 7.2x magnififation. Now, with the GG in place, the lens is projecting its image into a bigger target size (36x24mm) that the lens was designed for, and the DOF properties are retained. The camcorder then simply records this projection from the other side. Its just like the camcorder recording any other image, the DOF has already been rendered.

Its like taking a still image with your 35mm SLR cam, getting the picture back from the developers and then taking a picture of this with your camcorder, the DOF is already a part of the picture (or already part of the projection, in the case of the adapter).

Thanks for the reply Wayne. I thought this was going to end any possibility of grain and light loss, but the idea has been disproven. I'm glad I found your test video first though. Your explanation makes sense, but I sure wish it had worked.

mike, you can record the image straight from the slr lens with no gg. but like Wayne said, your still getting the same dof from your camcorder even without the slr lens. The only thing your doing is flipping your image. and without your gg. your acomplishing nothing. just a reversed image.

WAYNE!!!!, looking at your intitial test with the acid etch and the vaseline looks amazing. thats almost no light loss at all! can you tell me what type of acid cream you used and why did you have to rub vaseline over it. do you rub on the vaseleine after youve etched it, rub off the excess, and use stick it straight into the adapter without any type of seal? thanks. Im going to build a spinner and i was thinking about going for something like 220 grit ground glass. but your test shows practiliy the same amount of light with the aerial image off the slr. thats something i didnt think was possible without going for the expensive beatties. thanks in advance

Hi Forrest,

Yes this was some time ago. I used standard 'Armor Etch' cream to etch the glass. Once the cream is washed off with water, the vaseline is then rubbed on the etched side and then wiped off with a soft cloth. This gives a perminant 'wet look' and is the reason for the low light loss in that test.

Stay away from the acid etch, though, as its impossible to etch evenly and uniform. The vaseline worked the same with an aluminium oxide grind. When the SG35 was being shipped with a glass disk (most of the online footage) it was either a 320 or 180 grit grind, with the vaseline treatment. It really improves light transmittance without really compromising diffussion. The low grit size will ensure NO GHOSTING.

Awesome Wayne, i tried this on a ground plastic cd i made this morning, and it works great! Does it effect the diffusion of the glass, or is it just the same diffusion, but with better light transmission. Wayne, it seems you have made an extrodianry substitute to the beattie. And especially for spinning adapters because you can get rid of grain and dust. are there any con's to this type of setup, becuase i havent seen any yet. and if there isn't, are you selling your SG35's with this type of vaseline glass, bbecause you should be rich.

Forrest,
OK, i have sold units with this setup, and im glad you see the same results and enthusiam as i did when i found this out.

I have actually now found a material that has the same properties as the glass with vaseline applied, but its like this stock, so no vaseline, but with even better diffussion. This is whats now used on the SG35 and SGpro.

Does it effect the diffusion of the glass, or is it just the same diffusion, but with better light transmission

It does effect diffusion slightly, but its small, and the extra light transmittance and contrast is worth it!