Your sides are cut off....THAT's CHEATING! There is space on the left beside the pictures, see my posts...
But you don't seem to have the ghosting...RATS!
Give me hope I can fix mine(but your sides ARE chopped off)
Bud
But you don't seem to have the ghosting...RATS!
Give me hope I can fix mine(but your sides ARE chopped off)
Bud
For those that are getting ghosting, have you blacked out the ends of the prisms? I quickly looked through my prisms, and the only strange reflection I see internally is from the ends of the prisms. If blackened, hopefully, any light hitting that surface would be absorbed and not reflected. I know Mark is doing this, is everyone else?
I am but I went from black electrical tape to black construction paper...maybe i'll go back to the tape & see what happens. Here's a question to all...are you housings tapered or straight, meaning narrower at the pj end like the prismasonic or just a rectangular box?
Bud
Bud
Here is a thought in terms of the ends of the prisms that are possibly reflecting. Instead of just blackening the ends of the prisms, you could sand them down so they no longer represent a smooth reflective surface, and then of course blacken them out with paint, and then put something black beside them. Of course, then you would see if the actual faces you are projecting through are causing problems. Can't sand those down and paint em' ... lol 😎
Bud Bray said:
RATS? Here are some rats...
I can only work with what I have from the projector. This unit does have at least 5% overscan which I identified with the overscan pattern on JPK DVE...
Steve Scherrer said:
And I am just using black gaff tape right now. When you look into the end, it appears white (the sticky side of the tape), but it stops that light passing out the ends and refracting, so is a very quick, easy and cheap method of light control...
Bud Bray said:
Square foot print actually 🙂 with a large section cut away from one corner...
morkys said:
I did this with the water prisms - used fine wet and dry to dull the ends, but the ends still needed covering...
Mark
You both are blacking out the tops and bottoms of the prism as well, I hope? As well as the broad and thin end? Just doing a bit of sanity checking...
Sure are...
I am using 2 pairs of lenses so that may be my trouble(that and CARS credits REALLY emphasises the ghosting).
Keep experimenting. I'd rather have the ghosting on credits than major CA issues with 2 prisms only.
Bud
I am using 2 pairs of lenses so that may be my trouble(that and CARS credits REALLY emphasises the ghosting).
Keep experimenting. I'd rather have the ghosting on credits than major CA issues with 2 prisms only.
Bud
Also, as already experienced by others, I may just have a wonky lens combo going on...I'll try swapping some around again & see what happens. The picture I have is PHENOMINAL, so i REALLY don't want to rock the boat too much.
Also, just painted the inside of ANOTHER housing so have that as another test. ONE DAY I may even actually sit and WATCH A MOVIE! Could happen!
Bud
Also, just painted the inside of ANOTHER housing so have that as another test. ONE DAY I may even actually sit and WATCH A MOVIE! Could happen!
Bud
Lindahl said:
Well the case lid and base do that...
Bud Bray said:
I tried 4 of the CA series prisms I have (you guys have J series) and I could not get a very good stretched image without lots of reflections, so I simply went back to a 2 prisms lens. There is an even larger CA model out (8.5 x 7.5) and maybe two of those for the front optic and two of the current 7.5 x 5.5 prisms for the rear...
Bud Bray said:
I still haven't painted the inside black yet. I also made a slight change to the shape (in plan) compared to what is shown on the BLOG. The prisms angles are the same, but the case's front angle is slightly less than the previous 45degrees. There is a photo in the BLOG of this case, but unless you know, you might not pick the difference.
Basically instead of 80mm in from the front and the side, it is 60mm in on the front and 120mm in on the side. What I have found is that by havig a slightly longer side panel than the previous design, that I am not getting the side reflection as bad, even though the side is extended by just 40mm, it sppears to be making a difference...
Been to busy watching fims to pull the lens apart for painting 🙂
Mark
I suspect the 4-prism lenses are the culprit of the reflections, as they are pretty easy to make disappear on a 2-lens system. The chromatic aberration doesn't bother me all that much, so I don't think I need to go to a 4 prism set to begin with. But I also think that there are probably ways to minimize the reflections--rough up the edges, paint them black, etc.
Man, I have been away from this project for way too long. Time to get back into it.
Man, I have been away from this project for way too long. Time to get back into it.
Oh well, haven't switched housings yet. Like I said, it's only on black backgrounds with bright scenes...I can live with it.
Bud
Bud
Steve Scherrer said:
I would have to agree. If the 2 prism lens is aligned correctly, the amount of CA varies from very small to not noticeable...
Mark
My four medium-sized prisms (J24s) just arrived today! My projector (7205) arrives on Sunday. Then I get to start really playing with this stuff.
But I seem to be hearing two different ways to approach this. It sounds like I can make a single 2-prism lens, and that has CA but fewer reflections. Or I can make a dual 4-prism lens that reduces the CA, but has more reflection problems.
Can't we have it both ways?! I'll have my projector on the table top for a while and can easily play with the prisms. It sounds like most people have already got their's mounted and are less interested in messing with them now that they mostly work.
But I want more. I want to understand how this all works. I bought 4 prisms so I could make the dual-lens and get rid of any CA, so it just sounds like I need to find a way to identify and remove the reflections. It seems like removing the reflections with the 4-prism system is probably easier than trying to reduce the CA in the 2-prism lens.
I personally think that making the sides and top of the prism non-reflective is very important. Just looking into one of these prisms, you can see a lot of reflections caused by these surfaces. I don't think that just letting the top and bottom of the enclosure cover the top and bottom of the prism is good enough. I think the tops and bottoms of the prisms should probably be roughened just like the flat ends. I just have no idea how I'll "roughen" this crystal surface. But I'll play with various ideas and see what works.
I also think it might help to place a cutout at the front and back of the assembly that is fit to the actual needed rectangle of light. In other words, the square opening next to the projector lens will be just large enough for the beam of light from the projector. Then, an internal "baffle" between the two lens assemblies would be just large enough, and a final baffle on the output that is just big enough for the output beam. This would minimize any other light getting in, and might dampen some reflections.
But I'm really determined to try and figure this out. Maybe my enthusiasm will dampen after I've been messing with it for a couple of weeks, but I get to spend the entire Christmas break messing around in the theater with the new projector and these prisms and I'm really looking forward to it right now.
You can be sure that once I get going in a couple of weeks I'll be posting a lot and have some pictures. You guys have already done *so* much work on this, so I really want to donate some of my time to this also and try to make it even better.
Then I'll invite all of my HT geek friends over and get them hooked on CIH
But I seem to be hearing two different ways to approach this. It sounds like I can make a single 2-prism lens, and that has CA but fewer reflections. Or I can make a dual 4-prism lens that reduces the CA, but has more reflection problems.
Can't we have it both ways?! I'll have my projector on the table top for a while and can easily play with the prisms. It sounds like most people have already got their's mounted and are less interested in messing with them now that they mostly work.
But I want more. I want to understand how this all works. I bought 4 prisms so I could make the dual-lens and get rid of any CA, so it just sounds like I need to find a way to identify and remove the reflections. It seems like removing the reflections with the 4-prism system is probably easier than trying to reduce the CA in the 2-prism lens.
I personally think that making the sides and top of the prism non-reflective is very important. Just looking into one of these prisms, you can see a lot of reflections caused by these surfaces. I don't think that just letting the top and bottom of the enclosure cover the top and bottom of the prism is good enough. I think the tops and bottoms of the prisms should probably be roughened just like the flat ends. I just have no idea how I'll "roughen" this crystal surface. But I'll play with various ideas and see what works.
I also think it might help to place a cutout at the front and back of the assembly that is fit to the actual needed rectangle of light. In other words, the square opening next to the projector lens will be just large enough for the beam of light from the projector. Then, an internal "baffle" between the two lens assemblies would be just large enough, and a final baffle on the output that is just big enough for the output beam. This would minimize any other light getting in, and might dampen some reflections.
But I'm really determined to try and figure this out. Maybe my enthusiasm will dampen after I've been messing with it for a couple of weeks, but I get to spend the entire Christmas break messing around in the theater with the new projector and these prisms and I'm really looking forward to it right now.
You can be sure that once I get going in a couple of weeks I'll be posting a lot and have some pictures. You guys have already done *so* much work on this, so I really want to donate some of my time to this also and try to make it even better.
Then I'll invite all of my HT geek friends over and get them hooked on CIH
I've been playing with a lens masking as well(black construction paper). Haven't gotten too far so far, busy with other things. Currently I have the housing painted black, the prism ends & top & bottom sealed with black electrical tape and black construction paper along the insides to deflect any reflections...but CARS still shows ghosts on the credits. I'm also wondering about the picture settings...I have the contrast cranked way high & the brightness kinda down...i'll try playing with those settings & see what happens. BTW, aren't the J24's the SMALLER prisms?
Bud
Bud
You could maybe try taking the prisms to a glass etching place and have the edges made opaque to a depth of 1mm. .. and then paint matte black or whatever over them??
OK, I should have waited until I experimented a bit before I spoke 😉
I now understand what kind of reflections you are talking about. Coating the top and bottom isn't going to make any difference. That won't stop the *internal* reflections, and I can see that the main ones you want to get rid of are stopped simply by blocking the flat ends of the prism and having a decent case around the whole thing.
But here's what I did tonight. I didn't want to unmount my old projector from the ceiling yet (I'll do that when the new projector comes, but my wife will still want to watch movies in the meantime).
So, what I did instead was to use a laser pointer in the dark to try and get an understanding of the various reflections and see how different changes in the lens angles would effect it.
Using the laser pointer was *very* informative! For one thing, I definitely confirmed the previous statements that having the right-angles of the prism on the *outside* is better than having them on the inside. In other words, the 90-degree angle of the first prism is closest to the projector, and the 90-degree angle of the second prism is closest to the screen. This has a definite reduction of the number of reflections on the visible screen area. The total reflections are the same, but they get scattered to different angles and away from the main screen area.
Another interesting change was to move the entire lens assembly from side to side...keeping the same angle with the incoming beam, but just moving the lens left and right. As you get too far left or too far right, you can pick up a strong secondary reflection of the laser right at the screen.
Now, I need to think of how a single-beam laser will translate to a wide beam from the projector. But I think what this means is that if your prisms are too small and the left or right edges of the projector beam are hitting outside the "sweet spot" that it might cause some extra reflections to occur in some situations. I can see where it might matter exactly where the bright spots of the picture are (like the credits in cars, which tend to be along one side of the screen).
When the laser remains in the middle portion of the lens, then I still see a much much dimmer reflection on the screen that I haven't determined the source of yet. My guess is that this is one of those internal reflections that might be hard to get rid of.
Now that I understand that the outside coating of the prism isn't going to have any effect on the inner reflective surfaces, I'm not as confident as I was before about getting rid of them.
Note that these laser experiments were only done with a 2-prism lens. I haven't tried 4 yet. My guess is that the "sweet spot" area in the middle of the lens might decrease with the additional prisms. But I'll need to set things up a bit more accurately for more serious tests.
Has anyone else ever tried a laser? It's been a long time since I did any optics (although I *do* have a PhD in Physics...but it's been decades since I used any of it 🙂 But I'll continue playing with this and let you know what else I learn.
Hopefully this isn't all just old boring news 🙂
I now understand what kind of reflections you are talking about. Coating the top and bottom isn't going to make any difference. That won't stop the *internal* reflections, and I can see that the main ones you want to get rid of are stopped simply by blocking the flat ends of the prism and having a decent case around the whole thing.
But here's what I did tonight. I didn't want to unmount my old projector from the ceiling yet (I'll do that when the new projector comes, but my wife will still want to watch movies in the meantime).
So, what I did instead was to use a laser pointer in the dark to try and get an understanding of the various reflections and see how different changes in the lens angles would effect it.
Using the laser pointer was *very* informative! For one thing, I definitely confirmed the previous statements that having the right-angles of the prism on the *outside* is better than having them on the inside. In other words, the 90-degree angle of the first prism is closest to the projector, and the 90-degree angle of the second prism is closest to the screen. This has a definite reduction of the number of reflections on the visible screen area. The total reflections are the same, but they get scattered to different angles and away from the main screen area.
Another interesting change was to move the entire lens assembly from side to side...keeping the same angle with the incoming beam, but just moving the lens left and right. As you get too far left or too far right, you can pick up a strong secondary reflection of the laser right at the screen.
Now, I need to think of how a single-beam laser will translate to a wide beam from the projector. But I think what this means is that if your prisms are too small and the left or right edges of the projector beam are hitting outside the "sweet spot" that it might cause some extra reflections to occur in some situations. I can see where it might matter exactly where the bright spots of the picture are (like the credits in cars, which tend to be along one side of the screen).
When the laser remains in the middle portion of the lens, then I still see a much much dimmer reflection on the screen that I haven't determined the source of yet. My guess is that this is one of those internal reflections that might be hard to get rid of.
Now that I understand that the outside coating of the prism isn't going to have any effect on the inner reflective surfaces, I'm not as confident as I was before about getting rid of them.
Note that these laser experiments were only done with a 2-prism lens. I haven't tried 4 yet. My guess is that the "sweet spot" area in the middle of the lens might decrease with the additional prisms. But I'll need to set things up a bit more accurately for more serious tests.
Has anyone else ever tried a laser? It's been a long time since I did any optics (although I *do* have a PhD in Physics...but it's been decades since I used any of it 🙂 But I'll continue playing with this and let you know what else I learn.
Hopefully this isn't all just old boring news 🙂
Man, this is addictive 😎
Yes, you are right, the J24s are the "small". I thought I had ordered mediums, but after trying to remember I think I ordered small in hopes that I could squeeze it in.
I decided I couldn't do much without a real picture to ensure that I had the prisms set up correctly. So I went ahead and unmounted my old Sanyo PLV-60. After all, it was only going to be up there for another few days anyway.
But I was surprised how large the picture gets how fast! Good thing my new projector has a smaller lens. I'm not sure these "small" prisms (I'd hate to see how big the large ones are) would work for the PLV-60.
Anyway, it turns out that I didn't have the lens aligned quite right. So the last laser test isn't really valid. Once I got them set up correctly to stretch the screen by the proper amount, then I put the laser back and that side-to-side reflection problem is gone.
All I'm left with is the dim reflection that I can't get rid of. And this is still with a 2 prism lens.
I guess I also misinterpreted how the 4 lens system would work. I had originally assumed that you just made two 2-prism lenses and then put them in series. But now I can see that this is wrong because the picture grows in size too fast for this to work. I finally found the Bud's drawing on page 105 that I had somehow missed before. And now I see he is just doubling up each prism. I'll play with that a bit later and see what I get with the laser.
But right now I'm seeing a small secondary reflection on the screen just with the regular 2-lens system, so I'll start working with that.
This lens size *barely* fits the PLV-60. If I nudge one lens left or right just a bit, then it cuts off the image. Also, I'm doing this from a table-top, so the projector is shooting "up" to the screen. This required me to elevate the 2nd prism (closest to the screen) quite a bit to get the image to hit the prism in the middle. Just putting the two prisms on a flat surface in front of the projector wasn't good enough.
I know this is all pretty newbie stuff that everyone has probably already dealt with, but maybe it will help some other newbie get started with this.
I can certainly attest to the fact that playing with these prisms is really fun and it's amazing what kind of image you can get pretty quickly. Yes, I'm getting bowing at the top, but I know that can be fixed by the proper tilt angle. Right now my mission is to track down that reflection that I can clearly see with the laser.
Yes, you are right, the J24s are the "small". I thought I had ordered mediums, but after trying to remember I think I ordered small in hopes that I could squeeze it in.
I decided I couldn't do much without a real picture to ensure that I had the prisms set up correctly. So I went ahead and unmounted my old Sanyo PLV-60. After all, it was only going to be up there for another few days anyway.
But I was surprised how large the picture gets how fast! Good thing my new projector has a smaller lens. I'm not sure these "small" prisms (I'd hate to see how big the large ones are) would work for the PLV-60.
Anyway, it turns out that I didn't have the lens aligned quite right. So the last laser test isn't really valid. Once I got them set up correctly to stretch the screen by the proper amount, then I put the laser back and that side-to-side reflection problem is gone.
All I'm left with is the dim reflection that I can't get rid of. And this is still with a 2 prism lens.
I guess I also misinterpreted how the 4 lens system would work. I had originally assumed that you just made two 2-prism lenses and then put them in series. But now I can see that this is wrong because the picture grows in size too fast for this to work. I finally found the Bud's drawing on page 105 that I had somehow missed before. And now I see he is just doubling up each prism. I'll play with that a bit later and see what I get with the laser.
But right now I'm seeing a small secondary reflection on the screen just with the regular 2-lens system, so I'll start working with that.
This lens size *barely* fits the PLV-60. If I nudge one lens left or right just a bit, then it cuts off the image. Also, I'm doing this from a table-top, so the projector is shooting "up" to the screen. This required me to elevate the 2nd prism (closest to the screen) quite a bit to get the image to hit the prism in the middle. Just putting the two prisms on a flat surface in front of the projector wasn't good enough.
I know this is all pretty newbie stuff that everyone has probably already dealt with, but maybe it will help some other newbie get started with this.
I can certainly attest to the fact that playing with these prisms is really fun and it's amazing what kind of image you can get pretty quickly. Yes, I'm getting bowing at the top, but I know that can be fixed by the proper tilt angle. Right now my mission is to track down that reflection that I can clearly see with the laser.
OK, I made some nifty graphics. Hopefully I can figure out how to get a URL link to work.
I have laser-tested both the 2-prism and 4-prism arrangements. To summarize: in the 2-prism arrangement, I can get two secondary reflections...one from the side of each prism. So simply masking the small sides of each prism will eliminate these.
With the 4-prism arrangment, I get several more reflections. Most can be eliminated by masking the small sides. However, one set of reflections does not go away when the sides are masked. They do not appear to be coming from any of the sides, tops, or bottoms. They are coming from the surface where each prism touches each other I think.
Pictures are worth a thousand words, so here is the link to the page on my web site where I try to explain this: Mike's Anamorphic Experiments
The above link also has diagrams of both prism arrangements.
Based upon these results, I'm starting to think that the reflection in the 4-prism case might not be removeable. When I used a piece of paper to trace the source of this reflection, it was coming out of the main face of the lens, just like the main projector beam. So no amount of masking will remove this.
By the way, to reproduce these tests, just get a laser pointer and shine it into the prisms from the same angle and location as the projector beam. Then, move the laser back and forth across the surface, and rotate it to simulate the various light-paths from the projector. Some light paths have no reflections. Other light paths have more reflections. The diagrams that I put on the web site are the worst-case reflections that I could get to appear on the front screen. So you have to play with the laser a bit to get these to appear.
I have laser-tested both the 2-prism and 4-prism arrangements. To summarize: in the 2-prism arrangement, I can get two secondary reflections...one from the side of each prism. So simply masking the small sides of each prism will eliminate these.
With the 4-prism arrangment, I get several more reflections. Most can be eliminated by masking the small sides. However, one set of reflections does not go away when the sides are masked. They do not appear to be coming from any of the sides, tops, or bottoms. They are coming from the surface where each prism touches each other I think.
Pictures are worth a thousand words, so here is the link to the page on my web site where I try to explain this: Mike's Anamorphic Experiments
The above link also has diagrams of both prism arrangements.
Based upon these results, I'm starting to think that the reflection in the 4-prism case might not be removeable. When I used a piece of paper to trace the source of this reflection, it was coming out of the main face of the lens, just like the main projector beam. So no amount of masking will remove this.
By the way, to reproduce these tests, just get a laser pointer and shine it into the prisms from the same angle and location as the projector beam. Then, move the laser back and forth across the surface, and rotate it to simulate the various light-paths from the projector. Some light paths have no reflections. Other light paths have more reflections. The diagrams that I put on the web site are the worst-case reflections that I could get to appear on the front screen. So you have to play with the laser a bit to get these to appear.
MikeP said:
Very good posts MikeP, but your graphic shows the right angles inside, not outside 😉
I did this simply becuase the HYP of each prisms is the largest surface. My projector is extremely short throw, so I needed to maximise the surface area to ensure that the light beam is not clipped. It does work the other way as well, but I found that the best results came from having both right angles in.
The idea of reducing the input apperature is a good one, as even ISCO III does this.
The biggest problem for us is that the prisms are not multi-coated, so light reflections are going to be something we need to except.
The idea of blocking the small end of the prisms is also a good one, as it too will cause some light reflections through the diffraction properties of the prisms. Once all four suraces are blocked, the internal reflections are coming from just two sides - the prisms faces and happen because of the lack of multi-coating.
Your laser tests are cool, but I'm afraid that you've found other problems that even at the worst case, the likes of Bud, Steve, Paul and myself had previously not seen. The reflections I am getting are only visible of on the left hand side from about 1/3rd in to the edge and they are pale green streaks from the bright sopt. They are not visible on the rightl as your laser tests revealed...
Mark