Anybody w/static adapter have lots of grain? at DVinfo.net

Bill Porter · April 22nd, 2005, 07:20 PM

I built an adapter using Optosigma 1500-grit GG. I dialled in the focal length of my 35mm lens, to within a half a millimeter, using calipers and a professional photographer's eyeball and skill to confirm the infinity focus (we focused on a far-off pinprick of light, at night).

We opted not to use any macros as the ones I had, caused more flare. I simply use some spacers to put the GG at the minimum distance (~1.4") the camcorder is able to focus on. It's a little longer this way but eliminates the need for macros.

We dialled in the camcorder's focus in a controlled environment by making sure the 35mm lens was in focus, then and pointing the entire assembly at a wall with a test grid on it, and dialling in the camcorder using an LCD monitor. It is very well focused.

However I have a lot of grain, in my opinion. I will post some vids so you can see for yourself. I am wondering whether this is a byproduct of having everything so dead-nuts focused.

I could shorten the distance between the 35mm lens and the GG a half a millimeter or so, to cause the 35mm lens to project its image deeper into the GG (toward the smooth side), and/or I could pull the camcorder's focus back a bit.

Has anyone ever experienced this and has anyone ever reduced grain by changing focus on either group (35mm lens to GG, or GG to camcorder)?

Thanks!

Dan Diaconu · April 23rd, 2005, 12:13 AM

If you can see the grain, everything you did is right.
Moving the lens from focal plain will only shift distances.
If you re focus the camcorder, you will get rid of the sharp grain.... (somewhat).
That will work only as long as your iris is wide open. If you have to stop down, the grain will end up sharp again for it will be within the DOF of the camcorder’s lens.
What camera do you use anyway?

Bill Porter · April 30th, 2005, 08:33 PM

Good point about the camera's small aperture causing its DOF to deepen. I hadn't considered that.

I use a baby Panny, "just" a GS. What about you?

Also, I have a question for you about condensers. Have you tried condensers of various angles, and trying them at different distances from the GG? I see some people put them close but others like I believe it was the Daves, mounted them about 15mm away and found it gave a more balanced image.

I assume you want one with a wide angle of dispersion, and you want it far enough away that it spreads the hotspot across the entire lens. Therefore, the wider-angle the condenser, the closer you can put it to the GG.

Anyone?

Frank Ladner · May 4th, 2005, 10:09 AM

There was a trick mentioned before that you could do in After Effects (or most any NLE). Basically you'd capture the grain by itself and use that later to somewhat cancel out the grain in the video footage.

I started out back when Alain Dumais (sp?) mentioned the first static ground-glass adapter and have tried various grits. After months of playing around with this I got into microcrystalline wax, which in my opinion is the closest to grain-free that you can get with a static adapter. It has other advantages too, such as giving a more even (ie. less hotspot) image. It is pretty difficult to work with, though. (Check out some of the threads for more info. Also, some of my footage is here: http://209.214.235.122/mwtest)

I have come to the conclusion that the best solution is this:

- GLASS ground with a more coarse (500 micron) aluminum oxide
- ...Oscillating at fast speed

I say that because glass is best in terms of conserving light, and the bigger grit gives a more even and brigher image. If you use too small a grit, you'll have too much transparency and thus a bigger hotspot problem.

April 22nd, 2005, 07:20 PM	#1
Bill Porter Major Player Join Date: Mar 2005 Location: Ventura, California, USA Posts: 751	Anybody w/static adapter have lots of grain? I built an adapter using Optosigma 1500-grit GG. I dialled in the focal length of my 35mm lens, to within a half a millimeter, using calipers and a professional photographer's eyeball and skill to confirm the infinity focus (we focused on a far-off pinprick of light, at night). We opted not to use any macros as the ones I had, caused more flare. I simply use some spacers to put the GG at the minimum distance (~1.4") the camcorder is able to focus on. It's a little longer this way but eliminates the need for macros. We dialled in the camcorder's focus in a controlled environment by making sure the 35mm lens was in focus, then and pointing the entire assembly at a wall with a test grid on it, and dialling in the camcorder using an LCD monitor. It is very well focused. However I have a lot of grain, in my opinion. I will post some vids so you can see for yourself. I am wondering whether this is a byproduct of having everything so dead-nuts focused. I could shorten the distance between the 35mm lens and the GG a half a millimeter or so, to cause the 35mm lens to project its image deeper into the GG (toward the smooth side), and/or I could pull the camcorder's focus back a bit. Has anyone ever experienced this and has anyone ever reduced grain by changing focus on either group (35mm lens to GG, or GG to camcorder)? Thanks!

April 23rd, 2005, 12:13 AM	#2
Dan Diaconu Major Player Join Date: Dec 2004 Location: Vancouver, Canada Posts: 804	If you can see the grain, everything you did is right. Moving the lens from focal plain will only shift distances. If you re focus the camcorder, you will get rid of the sharp grain.... (somewhat). That will work only as long as your iris is wide open. If you have to stop down, the grain will end up sharp again for it will be within the DOF of the camcorder’s lens. What camera do you use anyway?

April 30th, 2005, 08:33 PM	#3
Bill Porter Major Player Join Date: Mar 2005 Location: Ventura, California, USA Posts: 751	Good point about the camera's small aperture causing its DOF to deepen. I hadn't considered that. I use a baby Panny, "just" a GS. What about you? Also, I have a question for you about condensers. Have you tried condensers of various angles, and trying them at different distances from the GG? I see some people put them close but others like I believe it was the Daves, mounted them about 15mm away and found it gave a more balanced image. I assume you want one with a wide angle of dispersion, and you want it far enough away that it spreads the hotspot across the entire lens. Therefore, the wider-angle the condenser, the closer you can put it to the GG. Anyone?

May 4th, 2005, 10:09 AM	#4
Frank Ladner Major Player Join Date: Aug 2003 Location: Poplarville, MS Posts: 453	There was a trick mentioned before that you could do in After Effects (or most any NLE). Basically you'd capture the grain by itself and use that later to somewhat cancel out the grain in the video footage. I started out back when Alain Dumais (sp?) mentioned the first static ground-glass adapter and have tried various grits. After months of playing around with this I got into microcrystalline wax, which in my opinion is the closest to grain-free that you can get with a static adapter. It has other advantages too, such as giving a more even (ie. less hotspot) image. It is pretty difficult to work with, though. (Check out some of the threads for more info. Also, some of my footage is here: http://209.214.235.122/mwtest) I have come to the conclusion that the best solution is this: - GLASS ground with a more coarse (500 micron) aluminum oxide - ...Oscillating at fast speed I say that because glass is best in terms of conserving light, and the bigger grit gives a more even and brigher image. If you use too small a grit, you'll have too much transparency and thus a bigger hotspot problem.