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Photo Forum / Film Photography / Darkroom / June 2006Looking for grainless plastic sheet
I'm looking for thin (ideally .010 or even thinner) plastic sheeting that's semi opaque/translucent - sort of like "milk jug" color, or maybe tending toward white - but with very little or ideally NO visible grain or striations, a completely even looking color/texture. As a comparison, very thin sheet mylar such as a graphics shop might use to print on is in the right neighborhood, but still has a small amount of grain. This is for rear projection of an image and I don't want any grain visible. Is there sucn a thing? I don't need a lot, probably a square yard, but realize I'll possibly have to buy more than I need due to the non-feasability of selling small quantities. Thanks for any info. > I'm looking for plastic sheeting for rear projection > ... Mylar such as a graphics shop might [quoted text clipped - 3 lines] > > Is there sucn a thing? No. Your best solution is to buy a foil made for rear projection. See B&H. This is an old problem, has been well analyzed and the products made for this purpose are the best you will do. Try DaLight, Elite, Draper etc. The matte surface of drafting Mylar is there so you can draw on it, it is not there for optical properties. A rear projection screen has a surface made for optical scattering, not graphite adhesion. Holographic rear projection screens have become a reality recently and you may want to explore this avenue. Last time I looked a small screen was ~$2,000. For conventional screens it is the grain that makes a rear-projection screen work. Each 'grainlet' works as a small prism and sends a little bit of the light in a skew direction. Enough grainlets and the light is evenly distributed. In general, the finer the grain the dimmer the image: each grainlet wastes a bit of the light and the finer the grain the greater the waste. A very fine screen has a very dim off-axis image. A grainless screen would be a sheet of clear glass: no off-axis image but a hell of a hot-spot. There are techniques using a combination of acid-etching and fine grinding that give a very fine grain yet high efficiency diffusing surface on glass. Regular ground glass is made with grinding or sandblasting and the resultant surface is not optimum for optical use. You can find what looks like a whitish grainless drafting Mylar but what you get is opalescent plastic with the same matte surface. This solution may give the appearance of no grain but the image will be diffused.  SignatureNicholas O. Lindan, Cleveland, Ohio Consulting Engineer: Electronics, Photonics, Informatics. Remove blanks to reply: n o lindan at ix . netcom . com f-Stop enlarging timers: http://www.nolindan.com/da/fstop/ > In general, the finer the grain the dimmer the image: each > grainlet wastes a bit of the light and the finer the grain the > greater the waste. A very fine screen has a very dim off-axis image. > > A grainless screen would be a sheet of clear glass: no off-axis > image but a hell of a hot-spot. I appreciate the info. I should probably clarify that what I want to use it for is projecting/capturing movie film. I've actually found a couple of materials that yield decent results but I can still detect a bit of grain in the resulting image, wondered if there's any way to get rid of it altogether. You mentioned grinding/etching glass, I had tried using 1500 grit wet/dry sandpaper on the mylar to see if I could cut down the grain, I don't feel it made a noticeable difference. > I appreciate the info. I should probably clarify that what I want to > use it for is projecting/capturing movie film. Then you don't need a screen at all -- project the film right on to the sensor chip or dup film. After all is said and done I think it would be cheaper to send the film to a transfer service than trying to cobble something together. > > I appreciate the info. I should probably clarify that what I want to > > use it for is projecting/capturing movie film. > > Then you don't need a screen at all -- project the film right > on to the sensor chip or dup film. How would this be accomplished? Wouldn't doing so mean I'd have to reverse the image with software? > After all is said and done I think it would be cheaper to send the > film to a transfer service than trying to cobble something together. Well, of course there's the issue of wanting to do it myself. Further, I only need a small amount of whatever material this would be. I already have a rig "cobbled together" and have gone to a fair amount of effort to do so, but I find the weak link in the chain is the projection surface. What I have now doesn't look unwatchable, but I feel it could be better, and given my disposition, I'm inclined to pursue that potential. >> > I appreciate the info. I should probably clarify that what I want to >> > use it for is projecting/capturing movie film. [quoted text clipped - 15 lines] > feel it could be better, and given my disposition, I'm inclined to > pursue that potential. The direct projection technique that the previous poster mentioned would likely require either special projection optics or imaging optics to prevent vignetting, so it probabaly would not be practical for you. Have you considered increasing the size of the projected image? This makes the grain smaller compared to the image. About 20 years ago, I saw a professional setup at a TV station used to broadcast movies. It had a projector and camera aimed at opposite sides of a transmitting screen. The image was about 4 or 5 ft across. Also, large F-numbers in the projection or collection optics will tend to emphasize the grain. If you think of each grain as a little prism, and if you have a very small aperture in both lenses, then there will only be one angle of the little prism that will direct light from the projector aperture to the imaging lens aperture. Prisms at other angles will appear dark. Larger apertures will allow for a larger range of angles. This is a simplification of what is really going on, but you get the general idea. SignatureAdam Norton Norton Engineered Optics Optical design and systems engineering for Silicon Valley and beyond. http://home.ix.netcom.com/~anorton/ (Remove antispam feature before replying) > Nicholas O. Lindan wrote: > > Then you don't need a screen at all -- project the film right > > on to the sensor chip or dup film. > The direct projection technique that the previous poster mentioned would > likely require either special projection optics or imaging optics to > prevent vignetting, so it probabaly would not be practical for you. It requires a whole big machine, vignetting is the least of it. The technology for converting film movies to video is as old as the TV. Most TV stations should have some big old dusty relic in a back closet. News footage was shot in 16mm so it should take small film and they may have an adapter for 8mm in case Mr. Zapruder shows up again. Movies are at 16, 20, or 24 frames per second and video is at either 30 or 25, so the machine stuffs in extra frames. Single frame a tape or DVD and you will see sometimes the frame is duplicated. You get rolling bars if filming a TV set, I am not sure what happens when filming a movie, I imagine if the VCR shutter is slowed down enough it may all blur together acceptably [Do VCR's have shutters? See how much I know on the subject.] I should stop babbling: Richard Knoppow is the resident guru on this subject. >> How would this be accomplished? Wouldn't doing so mean I'd have to >> reverse the image with software? Nooo. You will have to reverse the image if you use back projection, though. Most use a front surface mirror. For 8mm you may be able to rip the mirror out of a junk SLR and use it, else it's $40 at Edmund's. But reversing in software shouldn't be hard, just slow. >> Well, of course there's the issue of wanting to do it myself. Further, >> I only need a small amount of whatever material this would be. I >> already have a rig "cobbled together" and have gone to a fair amount of >> effort to do so, but I find the weak link in the chain is the >> projection surface. You might try front projection. Use a smooth white surface like mat board or foam core. Good enough for billions of Chinese. Speaking of which, I STR Sony announcing a VCR [DVR?] that would sync to a movie image and do the frame stuffing [there is some special word for this]. With Sony owning Columbia and Columbia screaming bloody murder about people taping new releases in movie theaters and then pumping out DVDs it seems odd that Sony should make a machine for doing just that. Hey, ain't Google fun: http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=003WXX > Have you considered increasing the size of the projected image? This makes > the grain smaller compared to the image. It seems that focusing on a smaller image gives a sharper final result. For some reason, it doesn't seem to be the same as taking a larger image and squeezing it down. I don't think I'm just imagining this. I also notice that seqments that are dark - i.e. there wasn't really enough light for the footage when it was shot, comes out better with the compact image. > It seems that focusing on a smaller image gives a sharper final result. > For some reason, it doesn't seem to be the same as taking a larger > image and squeezing it down. I don't think I'm just imagining this. I think what you are seeing here is the effect of the screen graininess that you are trying to get rid of. Grain has nice sharp edges to it. When it is large enough to be visible, it tends to increase the perceived sharpness since the image now has all sorts of sharp edges in it. I think if you try to characterize the actual resolution with a line-space test pattern, you will find it has not improved in a smaller image. > I also notice that seqments that are dark - i.e. there wasn't really > enough light for the footage when it was shot, comes out better with > the compact image. Again, you may be seeing the effect of screen grain which can improve the apparent contrast in dark images. If a portion of an image has a uniform brightness, some grains in that portion will appear brighter than the average and some will be darker. If the average brightness is just on the limit of detectability, the brighter grains will highlight that area. Any adjacent area that is completely dark will remain completely dark whether there is grain or not. Therefore the contrast in the shadows does appear to be improved. SignatureAdam Norton Norton Engineered Optics Optical design and systems engineering for Silicon Valley and beyond. http://home.ix.netcom.com/~anorton/ (Remove antispam feature before replying) Just another realization to add to my previous post. The smaller image will be brighter, so you probably are using a higher f/# on the camera. If your camera lens was not very good, this would improve the resolution in addition to the depth of focus. With a really good lens, the small f/# should not noticeably degrade resolution. SignatureAdam Norton Norton Engineered Optics Optical design and systems engineering for Silicon Valley and beyond. http://home.ix.netcom.com/~anorton/ (Remove antispam feature before replying) > > I'm looking for plastic sheeting for rear projection > A very fine screen has a very dim off-axis image. P.S. and because of what I'm using it for, off-axis image isn't a consideration. Try these folks...ain't google grand! http://www.da-lite.com/products/index.php?cID=10 > I'm looking for thin (ideally .010 or even thinner) plastic sheeting > that's semi opaque/translucent - sort of like "milk jug" color, or [quoted text clipped - 11 lines] > > Thanks for any info. > Try these folks...ain't google grand! > > http://www.da-lite.com/products/index.php?cID=10 I'd seen this before posting, but not quite what I'm looking for. > I'm looking for thin (ideally .010 or even thinner) plastic sheeting > that's semi opaque/translucent - sort of like "milk jug" color, or [quoted text clipped - 11 lines] > > Thanks for any info. Can you find an old rear projection TV at the junk yard, E-bay or garage sale? just a thought... Gregg >> I'm looking for ... rear projection [screen] > Can you find an old rear projection TV at the junk yard, E-bay or garage > sale? Now _that's_ a good idea! |
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