GG Reflection Issue at DVinfo.net

Dmitriy Uchakin · January 3rd, 2006, 02:52 PM

I was wondering if anybody had experience/problems with smooth side of the GG facing the optical path and the light loss that might occur from the reflection of light coming from the SLR. Diagram:

| - glass(smooth)
: - ground surface

SLR------|:------CAMERA

Would this arrangment be any different to that one:

SLR------:|------CAMERA

One the other hand, any UV filter that you put on your camera would theoretically loose light due to some of it being reflected from the smooth surface of the glass. Maybe its so negligible that we dont notice? Any thoughts, corrections?

Wayne Kinney · January 3rd, 2006, 03:03 PM

I can tell you that the SG35 has the ground side of the disk facing the camcorder.

Ben Winter · January 3rd, 2006, 09:19 PM

I think mostly everyone here has always pointed the rough surface towards the SLR lens as a rule of thumb. It makes more logical sense anyway--the ground-up surface is what diffuses the image, shouldn't it be on the side of where the image is coming from?

Dmitriy Uchakin · January 3rd, 2006, 10:27 PM

Thank you guys for the comments. Looks from the replies that both of options work fine.

Bob Hart · January 3rd, 2006, 11:59 PM

I favoured groundglass towards the camcorder for two reasons :-

For quick relay set up using the camcorder autofocus it can only decide upon the groundglass face because it can't see though it to the smooth face which might have specks and scratches on it if it is plastic.

Smooth glass on the rear, might create a reflective halation effect back onto the groundglass if there are strong poinpoint highlights in the image.

I did not discover by testing so I don't know if there is a problem. They are just the reasons why I did not go that route.

Dmitriy Uchakin · January 4th, 2006, 06:15 PM

Thanks Bob. I like your argument about protecting the final projected image from the dust and scratches that might appear on the smooth surface of the GG. It seems like autofocus or not, if you put the rough surface facing the slr lense, the final image will have to pass through smooth surface of glass before being picked up by the camcorder. And since its hard to keep the smooth side of the GG dust/speck proof, your camera will pick up that stuff.

Ben Winter · January 4th, 2006, 06:28 PM

I don't see how the smooth side would somehow attract more dust/specks than a rough ground glass side. Besides, the ground glass is in (almost) perfect focus (thanks to the deep DOF we're trying to avoid in the first place) even if the camera is focused on the smooth side, meaning any dust/scratches that appeared on that side would show up anyway.

Bob Hart · January 5th, 2006, 12:47 AM

Plastic CD-Rs when spinning in air, can be a dust magnet, especially for PVC shavings. The glass ones are not much better. Rough or smooth, as you suggest is not a real issue.

With an early glass disk, I had finishing problems with the final polish and there were minute smooth pits in the shiny surface on the outer edge and in the top third of the image frame. It did not seem to make any difference as these were off the focal plane. My device is a spinning disk so dust is not a real issue. So my logic to some extent is shot in the foot anyway.

With the smooth side facing the lens mount during a lens change, any bits that fall in from the dandruff scalp may be more visible on that shiny side.

A clean construction method and environment helps but kitchen table, back verander, carport, garage, backshed, out on a table in the backyard constructions, are not going to be dust free environments.

Many of the true to the revolution AGUS builds are going to be just that, hence my reasoning.

January 3rd, 2006, 02:52 PM	#1
Dmitriy Uchakin Regular Crew Join Date: Dec 2005 Posts: 48	GG Reflection Issue I was wondering if anybody had experience/problems with smooth side of the GG facing the optical path and the light loss that might occur from the reflection of light coming from the SLR. Diagram: \| - glass(smooth) : - ground surface SLR------\|:------CAMERA Would this arrangment be any different to that one: SLR------:\|------CAMERA One the other hand, any UV filter that you put on your camera would theoretically loose light due to some of it being reflected from the smooth surface of the glass. Maybe its so negligible that we dont notice? Any thoughts, corrections?

January 3rd, 2006, 03:03 PM	#2
Wayne Kinney Major Player Join Date: Jun 2005 Location: Brighton, East Sussex, UK Posts: 938	I can tell you that the SG35 has the ground side of the disk facing the camcorder. __________________ Thanks, Wayne.

January 3rd, 2006, 09:19 PM	#3
Ben Winter Trustee Join Date: Jun 2005 Location: Hollywood, CA Posts: 1,675 Images: 1	I think mostly everyone here has always pointed the rough surface towards the SLR lens as a rule of thumb. It makes more logical sense anyway--the ground-up surface is what diffuses the image, shouldn't it be on the side of where the image is coming from? __________________ BenWinter.com

January 4th, 2006, 06:28 PM	#7
Ben Winter Trustee Join Date: Jun 2005 Location: Hollywood, CA Posts: 1,675 Images: 1	I don't see how the smooth side would somehow attract more dust/specks than a rough ground glass side. Besides, the ground glass is in (almost) perfect focus (thanks to the deep DOF we're trying to avoid in the first place) even if the camera is focused on the smooth side, meaning any dust/scratches that appeared on that side would show up anyway. __________________ BenWinter.com

January 3rd, 2006, 10:27 PM	#4
Dmitriy Uchakin Regular Crew Join Date: Dec 2005 Posts: 48	Thank you guys for the comments. Looks from the replies that both of options work fine.

January 3rd, 2006, 11:59 PM	#5
Bob Hart Inner Circle Join Date: Dec 2003 Location: PERTH. W.A. AUSTRALIA. Posts: 4,477	I favoured groundglass towards the camcorder for two reasons :- For quick relay set up using the camcorder autofocus it can only decide upon the groundglass face because it can't see though it to the smooth face which might have specks and scratches on it if it is plastic. Smooth glass on the rear, might create a reflective halation effect back onto the groundglass if there are strong poinpoint highlights in the image. I did not discover by testing so I don't know if there is a problem. They are just the reasons why I did not go that route.

January 4th, 2006, 06:15 PM	#6
Dmitriy Uchakin Regular Crew Join Date: Dec 2005 Posts: 48	Thanks Bob. I like your argument about protecting the final projected image from the dust and scratches that might appear on the smooth surface of the GG. It seems like autofocus or not, if you put the rough surface facing the slr lense, the final image will have to pass through smooth surface of glass before being picked up by the camcorder. And since its hard to keep the smooth side of the GG dust/speck proof, your camera will pick up that stuff.

January 5th, 2006, 12:47 AM	#8
Bob Hart Inner Circle Join Date: Dec 2003 Location: PERTH. W.A. AUSTRALIA. Posts: 4,477	Plastic CD-Rs when spinning in air, can be a dust magnet, especially for PVC shavings. The glass ones are not much better. Rough or smooth, as you suggest is not a real issue. With an early glass disk, I had finishing problems with the final polish and there were minute smooth pits in the shiny surface on the outer edge and in the top third of the image frame. It did not seem to make any difference as these were off the focal plane. My device is a spinning disk so dust is not a real issue. So my logic to some extent is shot in the foot anyway. With the smooth side facing the lens mount during a lens change, any bits that fall in from the dandruff scalp may be more visible on that shiny side. A clean construction method and environment helps but kitchen table, back verander, carport, garage, backshed, out on a table in the backyard constructions, are not going to be dust free environments. Many of the true to the revolution AGUS builds are going to be just that, hence my reasoning.