I will be interested to read whether or not you find any difference between the turp and mineral oil. I read they both have the same refractive index.
I am getting closer to starting one of these myself. Most of the rest of my theater is finally in good shape.
I notice that the commercial folks are releasing a new model that uses solid acrylic prisms.
Anyone ever consider trying to use flexible mylar mirrors like the original Cineramas?
Anyone ever tried to use a commercial lens made for 16mm? Lots of these for relatively cheap on ebay. These are all stretch, though. I wonder if you could turn them around?
Gerald
I am getting closer to starting one of these myself. Most of the rest of my theater is finally in good shape.
I notice that the commercial folks are releasing a new model that uses solid acrylic prisms.
Anyone ever consider trying to use flexible mylar mirrors like the original Cineramas?
Anyone ever tried to use a commercial lens made for 16mm? Lots of these for relatively cheap on ebay. These are all stretch, though. I wonder if you could turn them around?
Gerald
I did try a 32mm projector anamorphic lens, it did work, except it cut off the corners. If you purchase one, you have to make sure it has a certain width at the base to work properly. If you can find one, this is a good option, however, the time it takes to find one may be longer than youw ant to wait and the price it will cost you may be the same amount or more than what you spent on materials to build your own two-prism version.
That's really interesting that the commercial foks are making a solid acryllic version, how might that work I wonder!!!! Tor, anyone? I have access to a plastics shop down the street, the guy said he could make anything one wanted out of plastic, of course to make such a prism might be quite expensive.
The solid version is great because no leaks, however, I wonder if it has the same barrel distortion, etc as the original did?
That's really interesting that the commercial foks are making a solid acryllic version, how might that work I wonder!!!! Tor, anyone? I have access to a plastics shop down the street, the guy said he could make anything one wanted out of plastic, of course to make such a prism might be quite expensive.
The solid version is great because no leaks, however, I wonder if it has the same barrel distortion, etc as the original did?
The acrylic lens will have barrel distortion because the surfaces are flat. Prismasonic has been using acrylic prisms for a while, I believe the ISCO series is also acrylic.
It should work well, but I doubt it's possible to do DIY because the surfaces need to be flawless.
In cinemas they use horisontally expanding lenses and project the picture on a curved screen. The curved screen eliminated the barrel distortion because the left/right edges of the screen are closer to the projector than the middle. This is not practical with a vertical compression lens as the screen would have to curve the other way (edges away from the projector).
Tor Arne
It should work well, but I doubt it's possible to do DIY because the surfaces need to be flawless.
In cinemas they use horisontally expanding lenses and project the picture on a curved screen. The curved screen eliminated the barrel distortion because the left/right edges of the screen are closer to the projector than the middle. This is not practical with a vertical compression lens as the screen would have to curve the other way (edges away from the projector).
Tor Arne
Tor I have two pictures now of the labels on the mineral oil if you need them. I tried 5 times to post them in here and the system keeps complaining about my picture size. I've met their criteria yet it still won't allow me to post in here (?). Drop me an email if you need them: barnes_jude@yahoo.com
Also: please let us know the results of mineral oil vs. turpentine oil
Also: please let us know the results of mineral oil vs. turpentine oil
For those that are using all-plastic prisms (I know there aren't too many), have you tried plastic-welding epoxy?
It's a different composition than standard two-component epoxy.
Things I've noticed about it:
It SMELLS until it cures. Use it outside, while it's most likely not dangerous inside it WILL smell.
It is EXTREMELY strong. I've used standard epoxy to bond plastic parts and it would often fail quickly, especially when warm. On the other hand, everything I've glued with plastic-welder epoxy has failed before the epoxy did.
I don't know how water-resistant it is, but I'm thinking of making a "first try" at an anamorphic prism using only plastic parts for simplicity.
It's a different composition than standard two-component epoxy.
Things I've noticed about it:
It SMELLS until it cures. Use it outside, while it's most likely not dangerous inside it WILL smell.
It is EXTREMELY strong. I've used standard epoxy to bond plastic parts and it would often fail quickly, especially when warm. On the other hand, everything I've glued with plastic-welder epoxy has failed before the epoxy did.
I don't know how water-resistant it is, but I'm thinking of making a "first try" at an anamorphic prism using only plastic parts for simplicity.
Entropy-- this was my original plan, too. In fact, my first version was all acrylic. There was a focus problem immediately and I had to discard it.
I think one of the problem with using it is, it bends much easier than glass, so, when you're piecing all of the sides together, if you put any additional stress whatsoever on any of the sides/corners when trying to secure a seal, you can end up with a slightly bent/tilted/twisted side where your image is passing through your clear acrylic.
If you use the fence post idea as your foundation I think this will be easier to do, because all you have to do is just rest the pieces nicely onto the one surface. However, make sure there's no uneven pressure exerted when trying to make your seal.
I also got some of the liquid epoxy which "welds" the acrylic together, I ended up not using it because my sides were so uneven. I think this could be re-investigated if one used the fencepost model. Press forward and let us know how it works!!!
I think one of the problem with using it is, it bends much easier than glass, so, when you're piecing all of the sides together, if you put any additional stress whatsoever on any of the sides/corners when trying to secure a seal, you can end up with a slightly bent/tilted/twisted side where your image is passing through your clear acrylic.
If you use the fence post idea as your foundation I think this will be easier to do, because all you have to do is just rest the pieces nicely onto the one surface. However, make sure there's no uneven pressure exerted when trying to make your seal.
I also got some of the liquid epoxy which "welds" the acrylic together, I ended up not using it because my sides were so uneven. I think this could be re-investigated if one used the fencepost model. Press forward and let us know how it works!!!
Others should chime in but I don't think the distance is critical in any way. In most cases you'll just want to hug them up to one another as closely as you can, if for the only reason but to save space. Mine to this day are STILL seperate, I set them up in about 15 seconds before each movie, I just put the projector in about the same spot each time, and, lean the smaller prism against the front of the PJ, the bigger one I prop into place by visually lining up the projected image into my 16:9 secreen dimensions.
Problems with my prototype
Ok, I built a prototype lens and was able to use it for a while, until today. While adjusting it, I dropped and broke the water prism. So, I figured I'd post some thoughts and questions, and then go back and start gluing another one together.
I haven't been able to make a prism that doesn't leak yet. I've tried to make 2 oil lenses and 4 water lenses so far and all of them have had at least a slow leak. Some of them had a not so slow leak. So any gluing techniques that you have to offer are very much apprecieated.
I was able to get a set of prisms with very slow leaks, so I built a shelf in front of my projector, and started aligning prisms. I first tried to expand the image horizontally. The barrel distortion was so bad, it made it almost unwatchable. But I was able to mask the top and sides enough so that there was only a very slight bow on the bottom. It was ok, but the image lost a lot of sharpness. It looked out of focus and the colors seemed much dimmer. Could this be because of the cheap picture frame glass?
Next, I tried the compression way. It worked much better than expanding, but there was pretty bad keystoning. The bottom of the image was narrower than the top. I didn't measure how much narrower, but it was definately enough to bug me. However, I haven't measured the angles of the prisms relative to each other yet, I've just been placing them in front of the projector and moving them around to see what looks the best. Has anyone else had this problem?
I'd post some pictures, but like I said, I broke the water lens so I've got to make another one. I'll put it together and take some pictures in a few days to show what I'm talking about.
Though I haven't given up yet, I've got to say I'm a bit dissapointed.
Ok, I built a prototype lens and was able to use it for a while, until today. While adjusting it, I dropped and broke the water prism. So, I figured I'd post some thoughts and questions, and then go back and start gluing another one together.
I haven't been able to make a prism that doesn't leak yet. I've tried to make 2 oil lenses and 4 water lenses so far and all of them have had at least a slow leak. Some of them had a not so slow leak. So any gluing techniques that you have to offer are very much apprecieated.
I was able to get a set of prisms with very slow leaks, so I built a shelf in front of my projector, and started aligning prisms. I first tried to expand the image horizontally. The barrel distortion was so bad, it made it almost unwatchable. But I was able to mask the top and sides enough so that there was only a very slight bow on the bottom. It was ok, but the image lost a lot of sharpness. It looked out of focus and the colors seemed much dimmer. Could this be because of the cheap picture frame glass?
Next, I tried the compression way. It worked much better than expanding, but there was pretty bad keystoning. The bottom of the image was narrower than the top. I didn't measure how much narrower, but it was definately enough to bug me. However, I haven't measured the angles of the prisms relative to each other yet, I've just been placing them in front of the projector and moving them around to see what looks the best. Has anyone else had this problem?
I'd post some pictures, but like I said, I broke the water lens so I've got to make another one. I'll put it together and take some pictures in a few days to show what I'm talking about.
Though I haven't given up yet, I've got to say I'm a bit dissapointed.
On leaks: I used this silicone-based bonding adhesive in a tube I purchased from a plastic shop, I've had great luck with it, no leaks.
The first model I built I used regular hot gun glue, just to see how it might work, and I already had the gun & glue from other projects. It had leaks everywhere but I eventually contained them.
Anyways, the adhesive I used last time (R5000 I think it's called?), just apply a nice bead down the length of your sides, and lightly set the glass in place, by doing so it seems to seal up any small areas that you might have missed. Go to your local plastic/acryllic shop and ask them what they would use to bond plastic and make it water tight. I bet you they'll hand you a tube of the same stuff I ended up with.
On dimming/etc. There IS definitely light loss, even if you use black sides to your prisms, there's all sorts of reflection and so forth going on in there, so the picture should be a little dimmer, but not that much. If you use more expensive (museum/anti-AV) glass it can diminish this somewhat, but IMO the loss in brightness doesn't equal the amount of money it costs to purchase the glass.
On colors being off: I haven't noticed this with mine, but I suppose it's probably due to the glass you're using. I suspect there's a big difference even between different types of cheap glass. I don't have any experience EXPANDING the image so maybe this is something that the prisms can't do well without other side effects.
On keystoning: I have a slight keystone on my picture more often than not. Remember that I set up my twop prisms ad hoc every single movie we watch. When it does occur it doesn't bother me enough to play with the prisms angles. I suspect that very slight adjustments left or right on the axis for either of the prisms negates or creates the keystone. If you play with the prisms long enough I think you can resolve the keystoning.
On barrell distortion: When I first setup my prisms I noticed barrel distortion along the top. The last 10-20 movies I've watched I haven't really noticed it. (??) Either my black masking at the top eats it up, or, the way I setup the prisms now doesn't create the barrell.
I think Tor and others posted in recent months that depending on the throw (ability of PJ to produce certain size image from a certain distance) of your projector, it can create more or less of this barrell distortion, this makes sense because you are asking the prism to compress a larger or smaller image to begin with depending on the throw of the projector.
The first model I built I used regular hot gun glue, just to see how it might work, and I already had the gun & glue from other projects. It had leaks everywhere but I eventually contained them.
Anyways, the adhesive I used last time (R5000 I think it's called?), just apply a nice bead down the length of your sides, and lightly set the glass in place, by doing so it seems to seal up any small areas that you might have missed. Go to your local plastic/acryllic shop and ask them what they would use to bond plastic and make it water tight. I bet you they'll hand you a tube of the same stuff I ended up with.
On dimming/etc. There IS definitely light loss, even if you use black sides to your prisms, there's all sorts of reflection and so forth going on in there, so the picture should be a little dimmer, but not that much. If you use more expensive (museum/anti-AV) glass it can diminish this somewhat, but IMO the loss in brightness doesn't equal the amount of money it costs to purchase the glass.
On colors being off: I haven't noticed this with mine, but I suppose it's probably due to the glass you're using. I suspect there's a big difference even between different types of cheap glass. I don't have any experience EXPANDING the image so maybe this is something that the prisms can't do well without other side effects.
On keystoning: I have a slight keystone on my picture more often than not. Remember that I set up my twop prisms ad hoc every single movie we watch. When it does occur it doesn't bother me enough to play with the prisms angles. I suspect that very slight adjustments left or right on the axis for either of the prisms negates or creates the keystone. If you play with the prisms long enough I think you can resolve the keystoning.
On barrell distortion: When I first setup my prisms I noticed barrel distortion along the top. The last 10-20 movies I've watched I haven't really noticed it. (??) Either my black masking at the top eats it up, or, the way I setup the prisms now doesn't create the barrell.
I think Tor and others posted in recent months that depending on the throw (ability of PJ to produce certain size image from a certain distance) of your projector, it can create more or less of this barrell distortion, this makes sense because you are asking the prism to compress a larger or smaller image to begin with depending on the throw of the projector.
I have heard of one incident where the turpantine had a slight yellow hue to it and colored the picture.
Some cheap glass is reflection-treated in a way that makes it unusable for projection. If you look through this type of glass it blurs anything that is at a distance from the glass, but anything close to the glass is sharp.
It is very important that you degrease the surfaces before you apply the glue/silicone. After degreasing you must also avoid touching the areas with your fingers as it will leave grease from your fingers on the glass.
If you tilt the lens you will notice the keystone changing, and also the geometric uniformity. The amount of compression at the bottom vs. the top of the picture varies with the angle of the complete lens assembly relative to the projector lens. Just try for yourself and note how it changes when you tilt it. Also try mounting it the other way around (upside-down). It works better one way than the other in my experience.
Horisontal expansion lenses are geometrically superior to vertical compression lenses because the angle of the light-beam hits the lens in the expansion-direction by equal amounts on both sides. But on a vertical compression lens the top of the light beam hits the lens at a much shallower angle than the bottom of the light beam. I'm not talking about the barrel distortion, but geometric uniformity (compression uniformity). This is something you will learn to understand while you experiment and make notes of the lens.
A vertical compression lens will give barrel distortion, while a horisontal expansion lens will give pincushion distortion (the corners stretch outwards).
Tor Arne
Some cheap glass is reflection-treated in a way that makes it unusable for projection. If you look through this type of glass it blurs anything that is at a distance from the glass, but anything close to the glass is sharp.
It is very important that you degrease the surfaces before you apply the glue/silicone. After degreasing you must also avoid touching the areas with your fingers as it will leave grease from your fingers on the glass.
If you tilt the lens you will notice the keystone changing, and also the geometric uniformity. The amount of compression at the bottom vs. the top of the picture varies with the angle of the complete lens assembly relative to the projector lens. Just try for yourself and note how it changes when you tilt it. Also try mounting it the other way around (upside-down). It works better one way than the other in my experience.
Horisontal expansion lenses are geometrically superior to vertical compression lenses because the angle of the light-beam hits the lens in the expansion-direction by equal amounts on both sides. But on a vertical compression lens the top of the light beam hits the lens at a much shallower angle than the bottom of the light beam. I'm not talking about the barrel distortion, but geometric uniformity (compression uniformity). This is something you will learn to understand while you experiment and make notes of the lens.
A vertical compression lens will give barrel distortion, while a horisontal expansion lens will give pincushion distortion (the corners stretch outwards).
Tor Arne
I think the most desirable would be all acryllic, because it's easier to work with and bond, and drill holes in, etc. But that's only if you can do it without blurring your image.
Tor's most recent models have been all acryllic, if I remember correctly. And as far as I know he still has not gotten that model to be completely 'in focus' on the corners.
Otherwise, I think glass on the front and back is probably the most probable to produce the least ill-effected, clean, image. The sides don't need to be glass or acryllic necessarily, but they should probably the least reflective material/color you can find.
In my opinion, the "best" model to date is acryllic sides (fencepost idea), and the glass front and backs just put in place. Ideally, this glass should be "museum" or other similar non-reflective glass. At the very least, the glass should be the type that when you look through it, your vision is not noticibly distorted in any way.
Tor's most recent models have been all acryllic, if I remember correctly. And as far as I know he still has not gotten that model to be completely 'in focus' on the corners.
Otherwise, I think glass on the front and back is probably the most probable to produce the least ill-effected, clean, image. The sides don't need to be glass or acryllic necessarily, but they should probably the least reflective material/color you can find.
In my opinion, the "best" model to date is acryllic sides (fencepost idea), and the glass front and backs just put in place. Ideally, this glass should be "museum" or other similar non-reflective glass. At the very least, the glass should be the type that when you look through it, your vision is not noticibly distorted in any way.
Acrylics are so difficult to work with. It's so difficult to achieve flat surfaces on the prisms with acrylic. And the slightest little over or underpressure inside will bend it. The only use for acrylic glass is if you're going to bend the surface to correct the barrel distortion or pincushion dirstortion. That makes the acrylic glass more rigid because it's bent. Acrylic glass is a very good light transmitter, better then the cheap glass.
BTW. If you make a horisontally expanding lens you can also make a curved screen which will give perfect geometry.
Tor Arne
BTW. If you make a horisontally expanding lens you can also make a curved screen which will give perfect geometry.
Tor Arne
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