Optosigma 1500 GG, Problem Solved

[Donnie Wagner]

I, like many others, have the optosima 1500 gg and had trouble with it because of too much transmittance. If you hold the gg up to a light, you can actually see the light through the gg (this problem has been discussed in some of the wax threads). I tried making a wax screen with little luck. So I continued to use my optosigma 1500. There was a tiny defect in my gg, so I ordered a new one. And in my tinkering I tried sandwiching the two together, with the gg surfaces facing each other. It worked!

Positive: No more aerial image, much better diffusion, and no more grain than a single optosigma gg.

Negative: Slightly more light loss than single gg

overall it's much better, I am happy now.

Give it a try!

[Wayne Kinney]

So im not the only one that see this in the Optosigma GG, I thought i was going mad. Thanks for pointing that out, Donnie.

Wayne.

[Madhav Yerella]

Hi Donnie,
It's a great find, considering that almost everyone using this GG had problems with either barrel distortion or overdiffusion of out of focus areas. I want to give it a try after I get some inputs from you

1) So are you using 2 numbers of part 099-0160 from this link
http://www.optosigma.com/miva/mercha...+%26+Apertures

2)And then gluing these 2 together with diffusion side facing each other?

3)Which camcorder and SLR lens are you using?

4)Is there a necessity of a condensor/diopter/magnifier in addition to the sandwitched GGs

5)By the way, do you know how your setup compares with Nikon D focus screen as a GG.

[Donnie Wagner]

Originally Posted by Madhav Yerella

"overdiffusion of out of focus areas"

Never heard of this problem, only underdiffusion beause of excess transmittance.

"1) So are you using 2 numbers of part 099-0160 from this link
http://www.optosigma.com/miva/mercha...+%26+Apertures"

YES

"2)And then gluing these 2 together with diffusion side facing each other?"

NO!!! They are just held together by retaining rings in a thorlabs 2" lens tube

"3)Which camcorder and SLR lens are you using?"

VX2000, super takumar 50mm f1.4, super takumar 35mm f2

"4)Is there a necessity of a condensor/diopter/magnifier in addition to the sandwitched GGs"

From what I've found, yes. I have a achromatic between my camcorder and the focusing screen(s). You can buy similar achromats for cheap at surplus shed

"5)By the way, do you know how your setup compares with Nikon D focus screen as a GG.

"

About the same, I have used a D screen

[Andy Gordon]

I've been down precisely the same path, I thought I'd solved all the problems with the Optosigma then noticed the diffusion from the aerial image. I tried two face to face and I think there's possibly more grain, need to test it some more but it seems like a good idea. With the Optosigma you need condensers, with a Takamur 1.4 lens I think the best solution is two 100mm FL condensers back to back between GG and cam (GS400), I've got 2x 120mm FL but still getting a little vignette on 36x24 image.

My results with Optosigma are much better than what I got with the Nikon D. I found the Nikon D much worse for vignette with the Takamur lens compared to Optosigma + 2x 120FL, and it still has exactly the same diffusion problem, and I think the grain was worse to boot.

I haven't been able to make a wax glass without horrendous grain, currently I'm putting together an oscillating version with a wax glass to see how that compares. Getting the glass to oscillate precisely in the XY plane with zero Z movement is the problem, but the unit I'm working on is the same size as the static adapter 56mm outside diameter, with a miniature disc vibrating motor.

Once I started editing footage from the Optosigma and adjusting colour curves, the grain and vignette I thought were gone became more apparent.

[Donnie Wagner]

[QUOTE=Andy Gordon]I've been down precisely the same path, I thought I'd solved all the problems with the Optosigma then noticed the diffusion from the aerial image. I tried two face to face and I think there's possibly more grain, need to test it some more but it seems like a good idea. With the Optosigma you need condensers, with a Takamur 1.4 lens I think the best solution is two 100mm FL condensers back to back between GG and cam (GS400), I've got 2x 120mm FL but still getting a little vignette on 36x24 image.
QUOTE]

Andy,
IF you've found that two condesors back-to-back works well, you should really beusing a single DCX lens instead of two PCX lenses. You'd eliminate the glass-to-air and air-to-glass transmittions which causes light loss and internal reflections. Also, try putting one PCX (aboout 150-250mm FL) against the back of your ground glass sandwich (||. And then put your DCX lens of about 250mm FL behind that to emuate the Movie Tube patent. It's worked really well for me. Also, from what I've found, the farther the GG is from the cameras lens, the less vingetting. When I started my whole setup fit in the Thorlabs 2" lens tube. Now it's nearly twice that long and I'm getting much better results. You'll need a strong achromat to help your camera, as you move the GG farther away. I got a 93 FL achromat for $30 from surplus shed. works great for me

Achromat- 250mm DCX- 150mm PCX- GG-GG-

The last three are all held together with two retaining rings...
The spacing kind looks like this

Camera- (|| () (||| 35mm lens

(|| Achromat
() DCX
(||| PCX + GG+GG

Hope that makes some sense

[Andy Gordon]

I was experimenting with the two condensers )( vs () and the the DCX (cemented doublet from Optosigma) was more expensive which is why I went for two, so yes the DCX would be better, it sounds like you've sussed it. I'll try the 250mm DCX from surplus shed ($1.50!!!) in combination with a 120mm PCX and see how it works. I moved the cam back to reduce the vignette, the tube is 100mm long total. With the GS400 I didn't need an achromat, it has no problem focussing.

Do you have any colour separation with your arrangement? I would guess not with such long focal lengths.

Cheers
Andy

[Donnie Wagner]

Umm, I would hesitate to put any lens in my system that costs $1.50. garbage in, garbage out.

[Andy Gordon]

Agreed but that was the only DCX I could find with 250mm FL, where did you get yours?

[Donnie Wagner]

Edmunds Optics, or Thorlabs

[Donnie Wagner]

sorry, Edmund Optics

[Rich Hibner]

are the optima's frosted side facing each other or away when you sandwich them?

[Wayne Kinney]

The frosted (ground) sides should be facing eachother touching. You want only 1 image plane, 2 will give a blurred result.