guys,
make sure you dont point the laser directly onto the camera lense. i heard the CCD goes for a toss if we do that, i dont know how far its true, but its better to be safe.

krishna

Thank you Krishna, I am not doing that. I am pointing the laser at a white paper and taking pictures of that.

I would not think of pointing a laser into my camcorder! :)

I am doing some more objective tests of the screen materials I have available.

Here I posted some software I developed for testing light loss on screens or lenses:

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

I found a bag material that has a transmission of around 96% which is fantastic (almost like regular glass), but has a rotationally variant diffusion, so two layers would be needed to create circular diffusion. This would bring the transmission down to 93%.

On the other hand a single layer of my thick pouch material offers circular diffusion with 95% transmission.

I still need to test the Office Depot tape which also offers circular diffusion... if we could only find it in wider format.

BTW, I would very much like to see anyone with a wax or a GG screen test it using my software test so we can compare results.

Alain,
I love the detailed work your doing in this area. Do your tests only apply to static glass solutions?

Thank you Wayne.

The tests methods I am developing apply to any system, both static or dynamic. Both types of systems use diffusion screens, so it is important that we can compare the different materials quantitatively. Only then can we objectively pick out the best.

The light loss computation is not perfect but will give us a good way to compare one screen to another. I will post the results of my tests of several materials, but I also want to encourage people with GG and wax screens to test them in the same way. That's why I am making the test software available to everyone.

Sounds good.

Im just wondering how changing more then 1 variable, say the device taking the image of the ground glass (scanner?) will effect the accuracy and consistency of the testing.

I am looking at that.

So far taking the image with a different camera and using different exposure settings doesn't affect the final transmission ratio.

But I will do a few more tests (scanner sounds good).

Well I tried the scanner and it doesn't work. The problem is that since the light has to come through the screen material, reflect on the background and come back, there is some reflection and that makes the screen area look brighter than the background alone.

Taping the screen materials to a computer monitor and taking a picture of that works best so far.

Ideally a transparency scanner would work best. But not many people have those. I will try with mine.

Yes true, light source needs to be behind the screen.

Here are some results from the Light Loss test:

http://mentemagica.com/35mmAdapter/S...%20bag%201.bmp
http://mentemagica.com/35mmAdapter/V...%20Bag%201.bmp
http://mentemagica.com/35mmAdapter/T...0Pouch%201.bmp
http://mentemagica.com/35mmAdapter/S...0layer%201.bmp
http://mentemagica.com/35mmAdapter/C...tector%201.bmp
http://mentemagica.com/35mmAdapter/O...e%20w-glue.bmp
http://mentemagica.com/35mmAdapter/O...0NO%20glue.bmp

The Veggies bag that I tested (your local veggie bag will differ) has the highest transmission of all materials. But, as I have noted, it does not give round diffusion. A double layered set with perpendicular layers would produce round diffusion but will drop the transmission to around 93% (0.966 x 0.966 = 0.933).

The thicker material is still the best with round diffusion and a high transmission of 95%. The Office Depot generic magic tape is next at 93.5%, but not wide enough to make a screen from it (much smaller grain than the thicker material).

For those who do not have a thicker material like the one I have, a double layer veggies bag aligned to give round diffussion is a good bet, with a 93% transmission (around the same as the Office Depot tape).

I am still looking for a bag with round diffusion and a transmission of 96% or more. If I find one I will try to get as much of that material as possible :)

PS. The images were generated with the updated version of the Light Loss Analysis software I posted earlier:
http://mentemagica.com/35mmAdapter/L...sAnalysis1.zip

Hey, I really have no idea what you are talking about in most of this stuff. But I did see that you haven't or anyone for that matter mention the material to laminate things. I have some of this and was going to try it on a "static gg" and haven't been able to yet, because I haven't got all the parts in. Seeing how you have this stuff down to a science you might want to look into it. If you can't find it in your country, I'd more than glad to ship some samples out to you.

Rh

But, you probably live in America, so yeah....

Thank you for your suggestion Richard. I will take a look. From what I remember this is a frosted type of material, so it really isn't the same type of polymer diffuser (or maybe it is) At any rate, I will test it.

I just did some tests to calculate the light loss of some of my lenses.

Canon coated wide andle lens (triplet): 97.5% transmission
Cheap plastic Fresnel lens: 97%
Sheet of common glass: 96%
Magnifier DCX: 95%
Slide viewer PCX: 92%

Ideally, we could possibly use a good lens system:

0.975 x 0.95 = 0.926 -> 92.6% transmission

(lens system X polymer screen= total transmission)

I assume that reducing the whole system to a single condenser (PCX or aspherical) would rate even better. Also note how a fresnel lens can be a good idea in terms of light loss (but getting a high resolution, distortion free Fresnel will be expensive).

So, in terms of light loss, the screen is not the only important factor.

(Note.- Intuitively I am guessing that rating a lens this way may not be correct since one would have to actually measure the whole amount of light that goes through the lens, but in my tests there wasn't much of a variation from testing a small sample area than measuring the whole lens area.)

I forgot to post the diffusion chart:

http://mentemagica.com/35mmAdapter/D...ngleChart1.pdf

Print the chart, fold it at the dotted line (90degrees) and place your screen material at the line. Shoot a laser pointer and see the diffused image on the chart. From it you can approximately gauge the diffusion angle of your screen.

Interestingly enough, more diffusion does not mean more light loss. One of my best screens (rated at 95% transmission) has the widest diffusion angle of all the materials I have tested.

Also I will soon post some promising tests using coated screens that have higher transmission.

Alain, did you receive and test your POC material?

I received three samples from them this week:

LSD5PC10
LSD20PC10
LSD30PC10

According to their documentation, this is 0.010" thick
polycarbonate with a 5°, 20° and 30° angle, respectively.

I also received my Beattie on Friday.

I’m not finished building my vibrating adapter, but at least I can compare the respective "brightness" of these screens with the setup I have, along with the Redrock M1 GG on my DIY spinning adapter.

I’ll be doing that in the next few days, before I install the Beattie more "permanently" in my vibrating adapter.

My test will be quite simple, and certainly not as scientific as the methods described here. I’ll put a chart on the wall and shoot the same frame in the same lighting conditions, from the same distance. I will let my GS400 set the aperture automatically for each screen, and then I will manually select aperture increments above and below what the GS400 has selected (for comparisons in my NLE afterwards).

Edit: I must add that my vibrating adapter does not have a condenser lens, so the POC would somewhat start with a disadvantage compared to the Beattie, which has a fresnel.

If anyone has suggestions or advice for this test, I’m all ears.