I would guess that the reflections you worry about are internally generated from the end plane of the prism. These will always exist, no matter how much black paint you use on the ends. However, if you can get the ends sand blasted, this reflection will become non specular, and should have a much less visible effect.
Hello Pink Mouse, have not seen you in this thread since back in the early days 🙂
According to the recent post by MikeP and his "laser" test, it appears that the issue is not internal, but rather from the faces themselves as they are glass after all which is by deault reflective. We are feeling that an optic coating may be the way to address this issue - just finding the right one at the right price...
I understand where your coming from too. So far as the paint or tape we put on the ends goes, it simply stops the light exiting the prisms at that point, but it does not stop light reflecting back from that surface as it is pollished and is shiny. Sand blasting might rough that surface helping to prevent the reflections we have...
Mark
According to the recent post by MikeP and his "laser" test, it appears that the issue is not internal, but rather from the faces themselves as they are glass after all which is by deault reflective. We are feeling that an optic coating may be the way to address this issue - just finding the right one at the right price...
I understand where your coming from too. So far as the paint or tape we put on the ends goes, it simply stops the light exiting the prisms at that point, but it does not stop light reflecting back from that surface as it is pollished and is shiny. Sand blasting might rough that surface helping to prevent the reflections we have...
Mark
I've been lurking! 🙂
When I said internal, I meant the inside surface of the end, rather than in the body of the glass itself. You have to remember that optically, the glass does nothing, what matters is the boundary conditions where the light has to transition from one material to another. Optical coatings help this by controlling the wavelength of light that is transmitted or reflected, look at a thin film of oil on water to see this.
When I said internal, I meant the inside surface of the end, rather than in the body of the glass itself. You have to remember that optically, the glass does nothing, what matters is the boundary conditions where the light has to transition from one material to another. Optical coatings help this by controlling the wavelength of light that is transmitted or reflected, look at a thin film of oil on water to see this.
So are you actually referring to the surface/air interface? If we rough that up, do you think it will help?
Mark
Mark
Yup. Sandblasting would be best to get a really rough surface with maximum diffusion, but also a coarse diamond sharpening stone should cut the glass enough to get an idea if it works or not
Hmm, I have a diamond stone too, so I might try that on one of my "bad" prisms.
But based upon playing around with the laser pointer, I don't think this particular reflection is coming from the inside surface of the ends. In fact, according to the laser test, the 2-prism lens shouldn't have this reflection at all, so I'm not sure where it's coming from. Tonight I'm going to test and see if it's coming from the screen reflecting back onto the prisms (I have a white screen).
I forgot to mention one other test I did last night with the grid test pattern. I tested the infamous "hypotenuse in or out" issue. In Mark's lens, the larger hypotenuse faces the lens so provide the largest surface area. In other lenses, the hypotenuse faces inward.
I tested both cases and did not see any CA differences with the grid test. In a way, this makes sense...the position of the 90-deg angle doesn't have any effect on the angle of the two prism surfaces. If you think about the path that the light is taking when it hits the prisms, you'll see that it doesn't matter which side faces the projector.
Tonight I'm going to test to see if the reflections change depending upon where the hypotenuse is placed. If the reflections are coming from the inner surface of the small end of the prism, then this could potentially change the angle of this reflection.
But based upon playing around with the laser pointer, I don't think this particular reflection is coming from the inside surface of the ends. In fact, according to the laser test, the 2-prism lens shouldn't have this reflection at all, so I'm not sure where it's coming from. Tonight I'm going to test and see if it's coming from the screen reflecting back onto the prisms (I have a white screen).
I forgot to mention one other test I did last night with the grid test pattern. I tested the infamous "hypotenuse in or out" issue. In Mark's lens, the larger hypotenuse faces the lens so provide the largest surface area. In other lenses, the hypotenuse faces inward.
I tested both cases and did not see any CA differences with the grid test. In a way, this makes sense...the position of the 90-deg angle doesn't have any effect on the angle of the two prism surfaces. If you think about the path that the light is taking when it hits the prisms, you'll see that it doesn't matter which side faces the projector.
Tonight I'm going to test to see if the reflections change depending upon where the hypotenuse is placed. If the reflections are coming from the inner surface of the small end of the prism, then this could potentially change the angle of this reflection.
I still say that it because by the fact that glass is reflective. Stand in front of any glass door or large window and you can see your self like a big mirror as well see through the glass. I believe out prisms are behaving in much the same way...
If we were to treat the glass and stop the reflections, that we would also stop this "lens flare"...
Mark
If we were to treat the glass and stop the reflections, that we would also stop this "lens flare"...
Mark
I agree Mark. It also makes me wonder about all of the projector brightness that we are losing to these reflections.
You've probably seen this too...the light inside on the walls of the enclosure is pretty bright. When I see this it worries me since that's light that isn't on the screen.
Of course, the screen *seems* plenty bright, so it's more of a theoretical issue than a practical one. I'm just a perfectionist and want the picture to be the best possible (well, ok, I'm a "cheap perfectionist" because I want it perfect, but I'm not willing to spend a million bucks on it 😉
You've probably seen this too...the light inside on the walls of the enclosure is pretty bright. When I see this it worries me since that's light that isn't on the screen.
Of course, the screen *seems* plenty bright, so it's more of a theoretical issue than a practical one. I'm just a perfectionist and want the picture to be the best possible (well, ok, I'm a "cheap perfectionist" because I want it perfect, but I'm not willing to spend a million bucks on it 😉
If the results are an improvement, you might want to think about doing the top and bottom of the prisms as well...😉
MikeP said:
Unlikely, I would have thought. Think how much the light has been attenuated from it's journey from the lens, (admittedly dispersion controlled), bouncing back of the screen, (diffuse, therefore square/cube law applies) then back off the relatively tiny prism surface, (again, non directional). That's got to be a pretty tiny amount.
pinkmouse said:
I have the tops & Bottoms covered with black tape...it holds the two together. So all is covered except the 2 faces. Some day soon(when I have time) i'm going to do a mask for the faces to just allow the PJ beam thru. See if it makes a difference.
Bud
Bud,
I think it will. Take a look at Prismasonic's prisms holders - small rubber attachments that go right around the prisms.
And ISCO III has a plate at the back (psrt of the mounting system) that restricts the width of the rear optic...
Mark
I think it will. Take a look at Prismasonic's prisms holders - small rubber attachments that go right around the prisms.
And ISCO III has a plate at the back (psrt of the mounting system) that restricts the width of the rear optic...
Mark
Hi, I am new to this topic and spent all last night reading from page 1!
What I was wondering is, if any of you have come across anywhere to get these glass wedges in the uk, or if any of the companies previously used will ship internationally as im having difficulty locating these here!
Thanks.
What I was wondering is, if any of you have come across anywhere to get these glass wedges in the uk, or if any of the companies previously used will ship internationally as im having difficulty locating these here!
Thanks.
You could email mfg directly and see if they ship to any distributors in the UK. That is what I did to get them here in Canada without having to pay duty or shipping charges from the states.
slothuk said:
I wish Tor Arne would come back. I often go over his posts from the beginning as he was very knowedgeable about this. In fact the idea of solid prisms are discussed there as well, just no one did anything about them...
It would be really cool to see his knowledge applied to SOLID CYRSTAL PRISMS where liquid leaking is not as issue...
Mark
Ok, here are my screen shots. I finally took down my 16:9 screen and put up a big sheet of blackout material to start working on a prism lens. My first lens is a two prism lens. The shots show bad angle from me lying on the futon and there is camera shake. Still, here they are:
C3P0 and R2
R2
Rebel B4 Darth Enters
C3 P0 on Tatooine
Leia
..and there you go. Again, another group of screen shots from the beginning of an adventure. Not mucn masking in this ghetto setup except for a board on top and a sheet of my left over velvet-ish masking material. I wanted to try it without much fuss so I simply put a board under-neath my projector:
...and put the prisms out in front. I may put the projector and lens on the same surface, but not before leveling everything. I measured the 16:9 projected image alone and then calculated 33% stretch divided by 1/2 and setup points on the left and right and stretched until I fit the new 2.37:1 shape.
I noticed that there was a huge amount of reflections to the side and the back and on the screen. I noticed that I didn't care much about the curved edges of the screen. I noticed that I didn't like that it looked as though the stretch may not not be uniform, and rotating pans showed varying degree of stretch. I noticed that although there may have been Chromatic Aberations and or poor focus to the sides, I didn't see that much.
The geometry is poor with the sides because the whole contraption is angled down (notice that the sides are wider at the bottom).
I have much work to do, but at least it is a start. I will try to build a box of sort, and/or start sanding and blacking out all the sides of the lens that are not used (top, bottom and sides). I guess I can try a 4 prism setup eventually.
I will take more photo's from a tripod as I progress. Thanx to all here who have helped. This is an interesting ride 🙂
C3P0 and R2
An externally hosted image should be here but it was not working when we last tested it.
R2
An externally hosted image should be here but it was not working when we last tested it.
Rebel B4 Darth Enters
An externally hosted image should be here but it was not working when we last tested it.
C3 P0 on Tatooine
An externally hosted image should be here but it was not working when we last tested it.
Leia
An externally hosted image should be here but it was not working when we last tested it.
..and there you go. Again, another group of screen shots from the beginning of an adventure. Not mucn masking in this ghetto setup except for a board on top and a sheet of my left over velvet-ish masking material. I wanted to try it without much fuss so I simply put a board under-neath my projector:
An externally hosted image should be here but it was not working when we last tested it.
...and put the prisms out in front. I may put the projector and lens on the same surface, but not before leveling everything. I measured the 16:9 projected image alone and then calculated 33% stretch divided by 1/2 and setup points on the left and right and stretched until I fit the new 2.37:1 shape.
I noticed that there was a huge amount of reflections to the side and the back and on the screen. I noticed that I didn't care much about the curved edges of the screen. I noticed that I didn't like that it looked as though the stretch may not not be uniform, and rotating pans showed varying degree of stretch. I noticed that although there may have been Chromatic Aberations and or poor focus to the sides, I didn't see that much.
The geometry is poor with the sides because the whole contraption is angled down (notice that the sides are wider at the bottom).
I have much work to do, but at least it is a start. I will try to build a box of sort, and/or start sanding and blacking out all the sides of the lens that are not used (top, bottom and sides). I guess I can try a 4 prism setup eventually.
I will take more photo's from a tripod as I progress. Thanx to all here who have helped. This is an interesting ride 🙂
Nice geometry 🙂
That R2 shot looks great, as does C3PO's round tummy thing. Good to see that your CA is small and limited to the sides. That Rebel solder looks very good...
So is that just from 2 J series prisms?
Well done Morkeys 🙂
Mark
That R2 shot looks great, as does C3PO's round tummy thing. Good to see that your CA is small and limited to the sides. That Rebel solder looks very good...
So is that just from 2 J series prisms?
Well done Morkeys 🙂
Mark
Yep. I used two medium prisms. I can no longer edit the post so the grammer mistakes will have to stay I guess...
In terms of my overall impression of the test, I was most disappointed with the reflections, lack of lumens and poor contrast in dark scenes. Since the low lumens and poor contrast are mostly due to the light lost to reflections, I am disappointed that the lens reflect so much. Whatever we do, this is light that will be lost from the projector, even once I block it from hitting the walls and screen.
Reflections were so bad that dark contrasty scenes were terrible with flares and reflections everywhere. Of course, with no masking anywhere, that is how it goes. I think the one big drawback of these prisms is not the focus and geometry, but that even with masking, we are probably loosing lots of light due to reflections. It would be nice to have a surface that doesn't reflect or absorb too much light, and passes as much of the light through as possible.
I was most impressed with the overall focus across the screen. The scene where Jason looks at all his fake identity passports and credit cards etc in Bourne Identity, the text looked quite sharp to the sides. It looked fairly good. Bright scenes really look good.
If anybody finds an anti-reflective coating solution, let us know 🙂
In terms of my overall impression of the test, I was most disappointed with the reflections, lack of lumens and poor contrast in dark scenes. Since the low lumens and poor contrast are mostly due to the light lost to reflections, I am disappointed that the lens reflect so much. Whatever we do, this is light that will be lost from the projector, even once I block it from hitting the walls and screen.
Reflections were so bad that dark contrasty scenes were terrible with flares and reflections everywhere. Of course, with no masking anywhere, that is how it goes. I think the one big drawback of these prisms is not the focus and geometry, but that even with masking, we are probably loosing lots of light due to reflections. It would be nice to have a surface that doesn't reflect or absorb too much light, and passes as much of the light through as possible.
I was most impressed with the overall focus across the screen. The scene where Jason looks at all his fake identity passports and credit cards etc in Bourne Identity, the text looked quite sharp to the sides. It looked fairly good. Bright scenes really look good.
If anybody finds an anti-reflective coating solution, let us know 🙂
Hey, looks pretty good so far. It's a constant tweaking experience...enjoy the ride! You probably have to angle them downwards more than you have to square up the sides better(watch they don't fall, i've broken 4 so far), Use duct tape to hold them down till you get a housing built(once you have the angles where you want them, also good to mask end reflections)
Looks good so far!
Bud
Looks good so far!
Bud