Please comment on my GG's light loss
 

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/showthrea...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.

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

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

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