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Alternative Imaging Methods
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Old February 15th, 2006, 07:46 AM   #61
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I have now redone the test with your 180RGB (was using pure 225 before) and the test now reads 95.3% - 97% so this sounds more like it.

Question, are you able to convert the %age to F-Stops lost?
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Old February 15th, 2006, 08:46 AM   #62
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According to my testing on the camera, as it correlates to the transmission numbers so far, 95% would correspond to a relative light loss of 1 to 1.5 F/stops with a 50mm F/1.4 under controlled chart conditions. More in the field.

Francois tested one of my early "coarse" GGs at around 90% transmission which is closer to 1.5 to 2 f/stops loss under chart conditions.

I'd postulate 5% being pretty close to 1 f/stop. The beatie at 97% is an approximate relative .7 F/stops loss. So 92% should be around 1.7 stops loss....of course assuming "adequate diffusion" which I suspect hovers from 15 to 20 degrees.

How does this hold up with your on-cam tests?
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Old February 15th, 2006, 09:07 AM   #63
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Thanks Dennis,

I will have to carry out some real world tests, shots with and without the adapter with the camcorder at a fixed iris.
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Old February 15th, 2006, 11:54 AM   #64
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Wayne the reason for using a 180RGB image is to give the digital camera some latitude. If you use a pure white image and take a picture of that, you may get everything blown out to white.

Now, to get a more precise measurement, we have to minimize the illumination variations along the monitor. The first step is to turn off all lights in the room so that the only light captured by the camera comes from the monitor. Second, the screen material should be placed near the center of the monitor so that two very adjacent measurements can be taken either to the side of the material or immediately below. I have found that in my CRT monitor I have less lightitng variation vertically than horizontally, so now I am making my measurements with the test boxes one on top of the other, instead of sideways. That gives me more consistent results independent of placement.

Finally, if you take the picture too close to the monitor the pixles will show up or you may get moire patterns. This will affect the readings as well. Making the test area larger will not improve the reading since the larger it is, the more variation in lighting it will pick up from your monitor. If the variation is not symetric the reading will be innacurate.

I will investigate the light loss correlation with f-stops.
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Old February 15th, 2006, 11:54 AM   #65
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Hey Alain,

Also, the other day I was in the Floral Dept looking at roses. Look at the bags they use. One side is shiny and the other side frosted. Check it out. Also these tests, are they dynamic or static?

Rh
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Old February 15th, 2006, 12:21 PM   #66
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Quote:
Originally Posted by Rich Hibner
Hey Alain,

Also, the other day I was in the Floral Dept looking at roses. Look at the bags they use. One side is shiny and the other side frosted. Check it out. Also these tests, are they dynamic or static?

Rh
Rich, you may have just found a single sided diffusion material. Have you tried it?

The tests outlined here are independent of the adapter being dynamic or static.
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Old February 15th, 2006, 10:35 PM   #67
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Alain,

Is that good or bad, I have not tried it(adapter in progess) Would you like me to send you some of it. I have a ton of it.

Rich.
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Old March 11th, 2006, 12:46 PM   #68
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Rich, were you at a Floral store or in a floral dept of a K-mart or something? im getting a high resolution network camera shipped to me next week and i need to upgrade from my static adapter that i made with a 1000grit aluminum oxide.

Alain, is there no grit size we can use to simulate this diffusion and minimal light-loss effects of a beattie or the POC materiel? Like, perhaps a 600 or 400 grit on one side of a plastic cd? of course it needs to be a spinner. or is that POC film glued over the cd a better solution for light-loss and bokeh? thanks.

also, for a test, i laid strips of the frosty off-brand scotch tape parrllel on one side of a plastic cd. so each strip overlapped its partner only by a bit. I applied the tape under running water to rid of all bubbles. kinda like how you apply window tint to car windows. anyways, the lightloss wasnt horrible but i would say it wasnt any better than my 1000grit, but it matched it pretty well.
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Old March 13th, 2006, 08:50 PM   #69
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The boquet or roses were at grocery store. I went back to look for some more and they're out right now. I'll see if someone else carries it.
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Old March 13th, 2006, 08:55 PM   #70
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Leave it to us alternative imaging guys to buy things just for their packaging. Thumbs up :)
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