Backlight the ground glass?

yzmotoxer807

yzmotoxer807

Well-known member
Just a thought: Since there always seems to be a problem with 35mm adapters losing a fair amount of light, would it be possible to somehow "backlight" the ground glass with white LEDs or something? Maybe shine them in at the edges of the ground glass?

Am I totally off base here? Has this been attempted?
 
Hi,

This would simply wash out the image, a little like taking an image in photoshop, and raising the black level.
 
Okay...I see. You know the other thing I just thought of was that it would probably make light streaks because of the convex lens on the one side of the ground glass (I am using a Canon Ee-A)
 
I've never used a 35mm adapter before, but I know that when I sneak my still camera into the movie theater to take pictures of the screen, I always bring plenty of batteries for my Canon Speedlite Flash.
 
What you re describing is like when you use a varicon or the panaflasher (or whatever it's called) to flash film as you shoot. When shooting color neg, these attachments raise the base fog density and basically light up the shadows. I'm not sure the results in a 35mm adapter would be great, but you don't know until you try :)
 
Well, You're not completely crazy! Cause I often wondered the same thing and I'm not crazy? Every time I would test one of my adapters without the body assembled, I would get a strange, brighter quality to it. It may be helpful to minimize grain in the black area. Like how the new cameras double and tripple sample the image then ratio it out for the highlight and shadow areas to get 1 multi sampled image with much more bit depth. Let's try it. I did a quick flashlight to the edge but this was so un scientific and bacame a sudden nuisance to what I was really trying to do . I remember back in the day about oh 20 years ago I worked in a photo studio and we would shoot copy work. Like old photos and things. To minimize the contrast we would shoot the image slightly underexposed and then double expose the image with a 50% grey card at 2 to 3 stops under exposure to minimize the blacks. I think you are not so off base with this and you've re-sparked my interest. I will test it properly and let you know my findings. Then Dennis can get a patent on it.

The whole brighter light thing, all has to do with photons and although you can't really excite a photon beyond it's current mass and charge, you can make them more dense by using a larger objective lens. This gives your lens a lower F# like F1.4 as oposed to F1.8
And then of course the most important rule of all, the inverse square law whereas... Well here's a link to something I wrote to help explain light gathering within an adapter a while back.

Post #42 here. http://www.dvxuser.com/V6/showthread.php?t=110922&page=5 starting about halfway down the post at 'Visible Light'

I think this may be not so crazy after all and may have slight benefits concerning black and dark areas. Or it may just wash out the image like Wayne said. Hummmmm
 
Years ago as a D.P. I was shooting a set made up with a lot of mirrrors and glass. It was a massive street scene set that was a TVC for a Glass manufacuring company . A big musical number that was all about the reflections.

I had a lighting gaffer try to tell me that we needed to throw light at the mirrors/glass so we could "see" the dancers and the singers. (ie .expose)

He took some convincing that the laws of light and physics do not work that way but eventually did it my way.

Hope I do not have to explain that again to anyone.
 
think about it how theatre and video projectors look with room lights on or off. essentially, adapters are mini rear projection screens.
 
Shibuya Oboya said:
think about it how theatre and video projectors look with room lights on or off. essentially, adapters are mini rear projection screens.
Click to expand...

That is a very good explanation of what will happen, imagine watching a video projector in the day time with the curtains open.
 
All you guys seem to think that he meant pointing a light at the ground glass from the camera side. Of course that would just reflect the light back at the camera which would suck. Just like watching a film being projected with the lights turned on.

But that was not my interpretation of what he was suggesting. He seems to be talking about having the ground glass internally lit by putting lights at the edges which would be completely different from what you all are describing as front lit projector screens. This would be more like the Arriflex VariCon I mentioned.
 
I don't see how that's substantially different. In both cases you are adding extra, unfocused light to the resulting image, light that has nothing to do with the scene you were trying to get a picture of. It will in fact lower the contrast in both cases. (It may be easier to control this phenomenon with the edge lighting you describe, but both are going to be equally ineffective at accomplishing what the original poster was thinking it would accomplish, i.e. "adding more light to the scene.")

Duncan
 
Yes you could obtain an effect similar to the Varicon (contrast control) but of course thats not required in the digital capture world where that is easily done with the setup. (Knee, Shoulder/ Ped etc...)

frobozz is correct. You can not "add" light to the scene / subject by this technique.
 
frobozz said:
I don't see how that's substantially different. In both cases you are adding extra, unfocused light to the resulting image, light that has nothing to do with the scene you were trying to get a picture of. It will in fact lower the contrast in both cases.
Click to expand...

The Varicon DOES lower the contrast. Shining a light at the front of the screen or glass or a mirror has the result of reflecting the light back at you. This is totally different than lighting up through a sheet of glass.

Here is a link to a page from the book "Cinematography" which describes how the varicon works. Link

It's basically a 6" x 6" glass filter that "glows" internally when a light strip along the top edge is turned on.
Click to expand...

Shooter said:
You can not "add" light to the scene / subject by this technique.
Click to expand...

I would say that bringing up/revealing shadow detail which is otherwise non-existant in your image is "adding" light to the scene.
 
It does not technically add light to the scene . It is "pre flashing" the areas of black by overlaying a "light haze" over the filter. The sensor or the film registers the "haze" only against the dark areas of the scene and it falls off towards the light areas.


None of this resolves the OPs quest for less light loss in the Adapter.
 
Shooter said:
It does not technically add light to the scene . It is "pre flashing" the areas of black by overlaying a "light haze" over the filter.
Click to expand...

I understand exactly what it's doing. My continued replies are simply because people are claiming that this is the same as turning on the lights in a theater or pointing lights at mirrors, which it is not.

Shooter said:
None of this resolves the OPs quest for less light loss in the Adapter.
Click to expand...

No argument there.
 
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