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Old January 21st, 2006, 07:24 PM   #61
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Yeah, I thought the bohek was the proper way to explain, but maybe not. It is like the background is not gaussian blurry, but rather sharp blurry and somewhat unnatural looking (this is with the spinning CD plastic bag). I guess Iwill have to do some screen grabs tomorrow to show you. It is really evident with outdoor shots. Also it is a shame because the indoor shots, even in low light, are amazingly bright!
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Old January 23rd, 2006, 06:55 AM   #63
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I have a possible explanation for the strange blur:

Ages ago I used a digital slr without a focussing screen (don't remember the name, though, some Pentax I think). You were kind of still able to see the correct field of view (right past some mirrors through the lens), but it was virtually impossible to get the focus right.

So based on this, here is my guess: The "bagscreen" is too translucent.
You get the sharp image (straight through the lens) mixed with the projection on the bag. So what you see is the shallow DOF image mixed with a long DOF image straight through the lens (but not diffused by the screen). Hence you get a blurred background with the unsharp objects having a somewhat sharp "core". This does also explain why the images are so unbelievably bright.

At the risk of sounding stupid, you could try to use two layers of the material. I would try myself, but I don't have such a setup yet.
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Old January 23rd, 2006, 07:48 AM   #64
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This is exactly what I've been dealing with my low diffusion GGs: http://www.dvinfo.net/conf/showthrea...t=58018&page=4
There are clips on that page demonstrating my adapter with a low and high diffusion GG. Normally this wouldn't be a big issue for film, as once the shutter is tripped, there is no place for the light rays to go past the film or CCD. With these adapters, there is almost an opportunity, if you want to look at it this way, to play with the image a bit as the camera is behind the normally impenetrable film/CCD plane.

The problem with thin films is that other than doubling or tripling the membrane, you can't tune the diffusion level. With a spinning GG, I'm finding you need a fairly coarse finish to achieve the look of a finite image plane....far coarser than this plastic material. I've now spent about $200 trying to get the "perfect" mix of adequate diffusion, and grain-free image on my little 85mm discs. What you see in the clips on page 4 are the extremes...too fine, and too coarse (at least at 1/250s shutter).
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Old January 23rd, 2006, 10:19 AM   #65
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Quote:
Originally Posted by Thomas Richter
I have a possible explanation for the strange blur:

Ages ago I used a digital slr without a focussing screen (don't remember the name, though, some Pentax I think). You were kind of still able to see the correct field of view (right past some mirrors through the lens), but it was virtually impossible to get the focus right.

So based on this, here is my guess: The "bagscreen" is too translucent.
You get the sharp image (straight through the lens) mixed with the projection on the bag. So what you see is the shallow DOF image mixed with a long DOF image straight through the lens (but not diffused by the screen). Hence you get a blurred background with the unsharp objects having a somewhat sharp "core".
Thomas, actually this is not the case. If you look at my diffusion tests earlier on this thread (where I first talk about the screen on my device) you will see that the diffusion is absolute, meaning that you cannot see anything past the screen after you have separated it from the image more than 1 cm. There is no "ghosting" or blending of images. This is why I took care to explain the difference between good diffusion materials and just translucent ones. I think the whole explanation (with tests) is on page 1 of this thread.

Dennis, this is a different issue than what you are having. As I just described.

Yesterday I found something that may explain the bad "Bokeh". Some of these thin-film material's diffusion is not invariant to rotation. This means that they spread light more in one direction than in another, this is very obvious when testing against a light source. The good news is that I found some materials that have rotational invariance, so in theory they should produce nice bokeh. I will test this later today.
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Old January 23rd, 2006, 10:52 AM   #66
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I'm not sure they're different issues Alain...but I'm no physicist either. My fine diffusion disc is absolutely opaque to an object a very short distance from it. In the light diffusion disc, I'm not seeing ghosting or blending...just a look that is not typical. I'll admit I'm no expert...so I'm happy to stand corrected if need be.
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Old January 23rd, 2006, 11:14 AM   #67
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Quote:
Originally Posted by Dennis Wood
I'm not sure they're different issues Alain...but I'm no physicist either. My fine diffusion disc is absolutely opaque to an object a very short distance from it. In the light diffusion disc, I'm not seeing ghosting or blending...just a look that is not typical. I'll admit I'm no expert...so I'm happy to stand corrected if need be.
Dennis, ok. I thought you were referring about a problem with ghosting, which definitely doesn't seem to be ocurring on this screen. But I will double check just to make sure. If it is happening I'll let you and Thomas know right away.
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Old January 23rd, 2006, 11:51 AM   #68
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Here are some new tests with a screen with less rotational variance:

(excuse the bad framing, I forgot to check that on the monitor)

http://mentemagica.com/35mmAdapter/AdapterTest36.jpg
http://mentemagica.com/35mmAdapter/AdapterTest36a.jpg
http://mentemagica.com/35mmAdapter/AdapterTest36b.jpg
http://mentemagica.com/35mmAdapter/AdapterTest36c.jpg
http://mentemagica.com/35mmAdapter/AdapterTest36d.jpg

As you can see there is some change in the blooming, but also there is more grain (not an issue for a moving adapter). Also, light transmission is even better.

Oh, and btw, I started a new thread to focus only on the screen issues. There are some pictures there of the rotational variance of the two different materials:

http://www.dvinfo.net/conf/showthread.php?t=58929

Last edited by Alain Bellon; January 23rd, 2006 at 02:35 PM.
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Old January 23rd, 2006, 02:24 PM   #69
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I was just taking a guess, based on my experience. I'm no physicist either. And I think your interpretation of the results sound better and very well reasoned.

And the new test .jpgs support your argument very well (and look great).

What I am thinking right now? Yippie, the bag idea is not dead yet. This is great news for me so I can upgrade my letus some time in the future.

Thank you Alain, I am honestly very grateful for your work.
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Old January 23rd, 2006, 05:02 PM   #70
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Ok, hopefully I willpost some home depot bag shot tonight with the spinning CD. It might be better or worse, I can't tell right now.
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Old January 24th, 2006, 10:43 AM   #71
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I just added vibration to my setup, so here is the new screen with no grain! The screen is bright.

http://mentemagica.com/35mmAdapter/AdapterTest53.jpg
http://mentemagica.com/35mmAdapter/AdapterTest53a.jpg
http://mentemagica.com/35mmAdapter/AdapterTest53c.jpg
http://mentemagica.com/35mmAdapter/AdapterTest53d.jpg

The are a bit over exposed and yes I didn't check the framing again, hehe.
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Old January 24th, 2006, 11:26 AM   #72
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Stills look great!
Any chance of posting a photo of your whole rig?
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Old January 24th, 2006, 11:47 AM   #73
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guys,
check these out

http://www.poc.com/lsd/default.asp?p...&sub=lsdsheets
and
http://www.poc.com/lsd/default.asp?p...w&sub=lsdfilms

i guess dan has used them once and refered lightloss as the issue. Its a trade off between light and grain. if there is no visible grain and probably 1 or 2 stops light loss, then i would go for it. and then its a lot more cheaper than rotating/vibrationg adapters.

krishna
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Old January 24th, 2006, 12:01 PM   #74
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Quote:
Originally Posted by M. Krishna Babu
guys,
check these out

http://www.poc.com/lsd/default.asp?p...&sub=lsdsheets
and
http://www.poc.com/lsd/default.asp?p...w&sub=lsdfilms

i guess dan has used them once and refered lightloss as the issue. Its a trade off between light and grain. if there is no visible grain and probably 1 or 2 stops light loss, then i would go for it. and then its a lot more cheaper than rotating/vibrationg adapters.

krishna
Excellent information Krishna. If you look at the film table, you will see that the polyester film has rotational variance (different diffusion angles horizonally and vertically). In the films I have tested the light loss is very little. I will certainly try these.

Thanks!
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Old January 24th, 2006, 12:30 PM   #75
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IS that with the new pharmaceutical bag? Darn it, that looks good!
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