Alternative Screens (thin-film, colloid, etc)

[Bob Hart]

I once contemplated finding the source for raw motor vehicle windscreen licence stickers, which seemed to work but were damaged when I tried to get the print off them. I found an AO5 dressed groundglass was better and did away with careful jointing of the gg material when sticking it onto the disk, so I didn't follow up on the stickers. The sticker material might be too coarse in texture.

[Alain Bellon]

Francois, actually the POC people didn't even reply to me at all.

If you don't want to perform a lightloss test using my software, I can do it for you. Hold the screen material against the computer monitor and take a picture with a digital camera as follows:

-Display a 180RGB gray image on your computer monitor.
-Hold or tape the screen material such that its lower right corner is at the center of the monitor.
-Place a digital camera on a tripod around 50-70 cm away from the monitor, disable the flash and turn off all lights (needs to be done at night).
-Take the picture.

From those images I can compare the brightness coming out unrestricted from the monitor with that coming through the screen material.

It should only take a few minutes, and if you send me the pictures I can analyse them and post the results back for everyone to compare.

I would really appreciate it :)

[Alain Bellon]

Originally Posted by Bob Hart

I once contemplated finding the source for raw motor vehicle windscreen licence stickers, which seemed to work but were damaged when I tried to get the print off them. I found an AO5 dressed groundglass was better and did away with careful jointing of the gg material when sticking it onto the disk, so I didn't follow up on the stickers. The sticker material might be too coarse in texture.

I will look into the material that you mention. So far I have found two types of plastic diffusers, one that looks like frosted plastic with a texture you can actually feel by touch, and the "holographic" type materials which diffuse based on a much smaller scale granularity and feel perfectly smooth.

The frosted type has been explored and has properties similar to that of ground glass. The smooth type is the one I am currently experimenting with.

[Francois Poitras]

Alain, OK I’ll try that tonight, and I downloaded your program, so I should be able to do the analysis myself.

[Alain Bellon]

Thank you Francois.

BTW, I just noticed that one of the links to my software got messed up by the "..." and I can't edit the post now. So here is the link again:

http://mentemagica.com/35mmAdapter/L...sAnalysis1.zip

and here is an image of a sample setup:

http://mentemagica.com/35mmAdapter/SampleSetup.jpg

[Dennis Wood]

Alain, just a note on the light loss experiments. I'm thinking that at 0 distance (against your LCD), light shining through the diffuser is mostly at 90 degrees to it on entry. I suspect that as you move the diffuser away, the difference between say a 5 degree diffusser and 30 degree diffuser would logically become greater in terms of transmission loss as incident angles increase. I wonder if the test would have more relevance if the flange to GG distance (average 44ish mm) was maintained.

Francois and I have pretty much done all the testing on the camera, same lighting, framing lens etc. but switching the diffuser material only...and then checking to see what the camera has chosen for exposure. To me this provides a better real world comparitive analysis. Just food for thought. I like your approach.

[Alain Bellon]

Originally Posted by Dennis Wood

Alain, just a note on the light loss experiments. I'm thinking that at 0 distance (against your LCD), light shining through the diffuser is mostly at 90 degrees to it on entry. I suspect that as you move the diffuser away, the difference between say a 5 degree diffusser and 30 degree diffuser would logically become greater in terms of transmission loss as incident angles increase. I wonder if the test would have more relevance if the flange to GG distance (average 44ish mm) was maintained.

Since the diffusion angle does not vary, the amount of light that goes through should be the same. I will try changing the distance from the monitor and see what that changes. At least if you test all your screens using the same procedure the test should be reliable.

Francois and I have pretty much done all the testing on the camera, same lighting, framing lens etc. but switching the diffuser material only...and then checking to see what the camera has chosen for exposure. To me this provides a better real world comparitive analysis. Just food for thought. I like your approach.

Your idea allows us to see the quality of the whole setup, not just the screen, so as an overall measure of the adapter it is a good one. We may systematize such test by doing a measurement by pixel brightness not just by eye. But we will need very controlled conditions (no sunlight, which varies within the minute, for example). The other thing is to use always the same exposure settings (as we have no way of knowing how the camera is choosing the exposure) and then compare the different brightness levels at different stops for plain camcorder and adapter shots.

What you propose is a great idea if properly handled for the adapter shootout that was proposed.

[Dennis Wood]

My basic technique so far is this:

1. In a dark room, I light up an ISO 122333 chart.
2. The camera and adapter are set up to frame the chart.
3. I switch the camera to manual, then toggle throught shutter speed and aperture, noting what the camera has decided to use. Therefore the camera (and not my eye) decides on exposure level
4. I then swap discs, or in the case of POC, swap samples, leaving the camera on, and on the tripod. Light, framing, distance, position are left exactly the same.
5. With the new sample/disc in place I toggle through the manual settings again, and note the new aperture settings chosen by the camera.

This is the best "relative" test that I could devise. It only applies to one system, but it evens out all the other variables. I like your light transmission concept, but there are so many differences in cameras, CCDs, gamma curves, panels, ambient light etc. I'm not sure how valid different results will be.

Perhaps the better question is this. So far, do your transmission results (from your software) correlate to actual light loss observed with the films in the adapter? If you can demonstrate this, you have a convert.

[Francois Poitras]

Beattie Intenscreen
Lo: 153 Hi: 157,6 Tx: 97%

POC LSD5PC10 (5°)
Lo: 144,7 Hi: 152,9 Tx: 94,7%

POC LSD20PC10 (20°)
Lo: 138,9 Hi: 149,3 Tx: 93%

POC LSD30PC10 (30°)
Lo: 140,9 Hi: 154,8 Tx: 91%

Redrock M1 GG
Lo: 123,3 Hi: 151,6 Tx: 81,3%

[Ben Winter]

Impressive. Thanks Francois!

[Alain Bellon]

Fantastic information Francois. I thank you as well.

I will try to make now a comprehensive chart of the tested materials so far. The only important material I would like someone to test is a microwax diffuser. (other materials are welcome of course)

The Beattie seems to rank around the same as the veggies bag. And ground glass seems to be on the bottom.

Also interesting is that the POC materials get less transmissive as their diffusion angle increases.

Francois, would you be willing to make a rough diffusion angle estimate of the Beattie?

I have the diffusion chart on the PDF file earlier on this thread. This will be a much rougher measurement but should give a good ballpark figure. You may also try the POC materials just to check for consistency between their angle measurement and the one in my chart.

PS:

Ben, a 180RGB image is just a bitmap with plain gray where the R,G,B values are at 180 in a 0-255 scale. I included a suitable file with the Lightloss software.

[Dennis Wood]

Well, I'll answer my own question based on Francois' test results. As we've compared most of these based on readings from our GS400s (with different adapters), his test results are reflected in the relative light loss with these different diffuser materials. So Alain, I'd say your method is returning pretty valid results based on what I've observed.

And yes, these results are incomplete for the purposes of evaluating diffusers in the absence of the diffusion chart.

I will say that the POC 20 has the best diffusion I've seen with any material yet. Bokeh is as fuzzy as can be with this material.


Consider me converted :-)

[Keith Kline]

That's interesting results. Just out of curiosity what exactly is this POC stuff? I looked through the thread and didn't see anything about it. Seems interesting though.

[Francois Poitras]

Alain, unfortunately, I don’t have a laser pointer. However, what I did do is hold the Beattie and the POC 20° side by side, in front of the LED of my LCD monitor, both at the same distance. I did the same with the POC 5°. I would roughly estimate the diffusion angle of the Beattie at 10-15°.

Grain size is what differentiates the POC. The 20° has a great bokeh and the grain appears to be finer than the Beattie’s. The POC 5° has bigger grain and would be more difficult to "blend" by vibration or oscillation.

I think POC sell kits of test discs which are a bit thicker but that contain a 15° sample.

Keith, see post number 30 above. POC stands for Physical Optics Corporation, www.poc.com.

[Keith Kline]

Thanks for the info. I recall someone posting about that site awhile ago, but I didn't know that anyone contacted them and got some samples to test. I'm working on a spinner based loosly on the DIY redrock guide and am looking for a better solution for the GG. This stuff seems promising. Will they sell in small quantities? I wouldn't mind getting some to try with a spinner to see the results. Thanks for all the info.