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.

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 :-)

Poc?
 

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.

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.

Thanks
 

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.

Wow, I have POC 30 and the grain is huge when compared with my GG (???)

Keith,

You may want to try checking sandwich bag materials (or veggies or some such). They offer more light transmission than the POC materials. Just check their diffusion because if the diffusion is not circular your bokeh will not be as pretty.

The most beautiful bokeh I have got is from a double layer Tx96.6% veggie bag (perpendicular so diffusion is circular). But transmission drops to 93% due to the double layer. (which isn't actually too bad)

Dennis, I am glad you are converted. Resistance is futile.

Jim, I'm pretty sure the 30 has too much diffusion/light loss. The 20 has very good diffusion (better than anything I've made), but I think 15 (which I don't have yet) is the likely ideal.

Comparing the many GG's that I've made, the finer ones simply did not diffuse enough....some liked the look, but many pointed out wierd bokeh. The grain of my latest favourite GG matches the LSD 20 pretty closely, but there's no question that the 20 has more controlled diffusion...and at least .7 f/stops better light gain.

Forget static with these....the grain is way too big. It must be moved...and quickly. I am testing some spinnners with AR coatings and 1 micron surface relief. Should be interesting to see how they compare with the POC samples.

Hmm... I've been thinking 60 or greater POC parts would be better suited for the GG as their grain is less visible, but of course the uphill battle with them is severe light loss. To a point, I'm not that hung up on what the bokeh looks like, quite frankly, nearly so much as I am getting grain as supressed as possible while losing as little light as possible.

I've got an 80 degree POC diffusing film sample. Way too much light loss, forget it.

You're right Jim, it's somewhat subjective. I can get zero grain with 1 f/stop light loss, super sharp etc. with my less diffuse GGs. Problem is when I post something with that GG, I get the "looks like a promist filter" comments. You won't see it in darker footage as much as light stuff, particularly specular highlights.

I'm convinced so far that the 20 degree POC LSD (and more likely the 15) has got the "right" amount of diffusion. Better than anything I've seen yet. It also corresponds both in terms of static grain and diffusion levels to my GG that has produced the greatest positive feedback. The upside is the the POC does it with .7 F/stops relatively less light loss.

Jim, if you don't care for bokeh, use a sandwich/veggies/home depot bag. It will give you small grain and the best light loss. Much better than the POC materials. You may even get lucky and find one with circular diffusion and then your bokeh will look great as well.

Here is a compiled table of all materials tested so far:

Beattie Intenscreen
Diffusion angle:~15° Transmission: 97%

Veggies Bag
Diffusion angle:~5x20° Transmission: 96.6%

Thick pouch + Coating on one side
Diffusion angle:~5-7° Transmission: 96.2%

Sandwich bag 2
Diffusion angle:~5x25° Transmission: 95.3%

Thick pouch
Diffusion angle:~15° Transmission: 95.1%

POC LSD5PC10
Diffusion angle:5° Transmission: 94.7%

Sandwich bag 1
Diffusion angle:~5x25° Transmission: 93.5%

Office Depot Magic Tape
Diffusion angle:~15° Transmission: 93.5%

POC LSD20PC10
Diffusion angle: 20° Transmission: 93%

POC LSD30PC10
Difussion angle: 30° Transmission: 91%

Redrock M1 GG
Diffusion angle: ? Transmission: 81.3%

"Sandwich bag"
 

Alain, could post some pictures of the wonderful sandwich, veggies etc bags...I'm looking for one here in Norway....but can't spot any of these...Thanks.

I also wonder which kind of GG the Letus35 Flip uses....

My guess would be hand ground or pre-ground, 1500 grit glass.

I beleive it to be 600 grit, which is an excellent choice for a vibrating adapter.

Letus 35 improvement
 

So replacing the GG grit by a Beattie Intenscreen should per def bring huge improvements to the picture. Right ?

http://www.dvinfo.net/conf/showthread.php?t=58599

Ben's thread on same subject.

Changing the GG to one of these holographic diffusers (POC, Beattie, Bag) will reduce the lightloss, but it may not make your picture better.

For example, here are some quick images of the bokeh produced by a couple materials. They are taken with a 50mm lens with the focus ring pulled all the way towards the near end (excuse the dirt, but was a really quick test swaping the screens):

Thick material (~7°, 95.1%):

http://mentemagica.com/35mmAdapter/B...-Thick1-sm.jpg

Thick material coated (~15°, 96.2%):

http://mentemagica.com/35mmAdapter/B...Coated1-sm.jpg

Sandwich double layer perpendicular (~15°, 91%)

http://mentemagica.com/35mmAdapter/B...chPerp1-sm.jpg

Andy Gordon posted an image from the Beattie bokeh (~15°, 97%):

http://imagedump.filefactory.com/full.php?id=2514

As you can see, light transmission is not the only factor here. The Beattie looks very similar to my thick coated material: Bright hotspot right at the light point and then a fuzzy haze.

But the sandwich bag double layer (unfortunately the lowest transmission of the 3), gives the "nice" circular disks some of use like to see.

At this point I really do not know if there is a way around this. Any thoughts?

Alain,
Tried your software light transmission test on the SG35's GG material, and it reports 97 - 99% depending on where i place the boxes. Im not sure if this is correct or im doing something wrong with the software.

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?

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?

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.

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.

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.

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.

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.

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.

Leave it to us alternative imaging guys to buy things just for their packaging. Thumbs up :)