Not sure if this has been posted yet or not, but found an interesting article discussing anamorphic prisms... http://ej.iop.org/links/rSFnK9YpC/oA6MGC-R2xGNSkyMav5vpA/jdv23i7p768.pdf
Another great read on using 4 prisms.
http://www.opticsinfobase.org/Direc...id=28306&seq=0&CFID=37815313&CFTOKEN=22427922
http://www.opticsinfobase.org/Direc...id=28306&seq=0&CFID=37815313&CFTOKEN=22427922
Pagercam said:
I just received a couple of J24 and J26 prisms and measured them with micrometers. Their angles are very close, so close that I couldn't tell a difference just by looking at them, but after calculating the angles, they are slightly different.
The J24 has an angle of 8.0 degrees, and the J26 has an angle of 8.5 degrees. I don't have a J25 so I couldn't measure it, but it's probably very close to 8 degrees, too.
Sorry I didn't get around to measuring the angles--the holidays are a lot busier for me that I thought! I haven't touched my prisms in a while.
Anyway, my 5 deg. measurements were very crude, so it doesn't surprise me that the angles of the prisms are a little more than that.
Anyway--Don't know how much time I will get to devote to this in the next few days, so Happy Holidays to all! This forum has been really fun.
Anyway, my 5 deg. measurements were very crude, so it doesn't surprise me that the angles of the prisms are a little more than that.
Anyway--Don't know how much time I will get to devote to this in the next few days, so Happy Holidays to all! This forum has been really fun.
mmmkam said:
When I originally started reading this thread, I also had this kind of question. But after playing with the prisms, what I have learned is that each setup is slightly different. It depends upon the size of your screen, the projector throw distance, etc. There is no single "correct angle" answer that can be given.
The best advice is to just get your prisms and then set them up on a table (or tall ladder, depending upon your projector setup) and just play with them for a couple of hours. It's really very easy to set them up and then just adjust them to stretch your image however you want.
When I was ready to make my enclosure, I placed the prisms on a piece of paper. Then I adjusted the prisms while my projector was sitting on a table at the correct distance from the screen. Then I used a pencil to draw the outline of the prisms onto the paper. This gave me a guide when making the enclosure.
But when I built my enclosure, I made sure to allow the prism angles to be adjustable. Then when it was all mounted to the ceiling, I could tweak the prism angle so that it was just right.
Regarding the discussion of the angles of the different prism sizes: I highly recommend that newcomers just purchase two prisms of the same size. If you don't think the small prisms will work, then buy two of the medium size. While it is possible to mix a small prism with a medium prism, and difference in their internal prism angle will cause color artifacts. Remember that the first prism is splitting the light beam into a rainbox, and the second prism is taking this rainbow and reintegrating it into a single beam of light. If the prism angles aren't identical, then you will end up with a slight rainbow on your screen. It might be minor, but why mess with it? Your enclosure will still need to be larger to accomodate the largest prisms, so you might as well make both prisms the same size.
mmmkam said:
It may be a great read, but unfortunately for those of us without a subscription to the online journals, it looks like they want $22 to download this article.
Ed
MikeP said:
Yeah, I agree with this wholeheartedly. It seems to be much easier to set up by experimentation than by trying to theoretically calculate the angles you need.
By the way, I have some first impressions on using the glass prisms vs my original acrylic/water prisms. In a way I was a little bit disappointed because I was hoping that using glass would reduce the amount of pincushion I get, but this doesn't seem to be the case. In this respect, the glass prisms seem to perform very close to the water prisms. Building a curved screen is not an option, so I'm just going to have to mask off the edges.
Regarding astigmatism, I'm finding that the glass prisms definitely has less astigmatism of the water prisms, but doesn't eliminate it completely (at least not with my setup of a Panny 100ax with a throw ratio that is currently 1.8). A reduction in astigmatism essentially improves the image clarity, so the glass is a definite improvement.
Lastly, and I admit I have to do a lot more work to do, but I have to say I'm a little bit disappointed in how much CA there is with two glass prisms. I tried various configurations, 2 prisms, 3 prisms (don't laugh), 4 prisms, and even a combination of water and glass prisms. The best configuration I have found thus far for reducing the CA seems to be 4 prisms (2 J24s and 2 J26s), but I still have a lot of experimentation to do. Like I said, these are first impressions.
Unfortunately, I'm going to be out of town for about a week, but I'll continue tweaking them when I get back.
Ed
torsteinvh
I don't know if this will help, but I purchased some prisms in the U.K from:
http://www.freecad.uk.com/acatalog/Sapphire_Clear_Crystal_Wedge.html
They're pretty heavy, so the shipping to Norway might be just as expensive...
I don't know if this will help, but I purchased some prisms in the U.K from:
http://www.freecad.uk.com/acatalog/Sapphire_Clear_Crystal_Wedge.html
They're pretty heavy, so the shipping to Norway might be just as expensive...
pecksniff
Was wondering how well those wedge's work as ive been looking for somewhere to get them in the uk?
Was wondering how well those wedge's work as ive been looking for somewhere to get them in the uk?
slothux
The wedges from Brunel Engraving seem to be manufactured in the far east, and as far as I can tell are almost identical to those mentioned in these threads. They are 6"x4" with a base of 1.25" angled approx. 8 degrees. They also come in a very snazzy little box!
At the moment I have only "fiddled" with them, and they certainly work,
but until I've tried them full-scale I can't comment on things like bowing and reflection.
The wedges from Brunel Engraving seem to be manufactured in the far east, and as far as I can tell are almost identical to those mentioned in these threads. They are 6"x4" with a base of 1.25" angled approx. 8 degrees. They also come in a very snazzy little box!
At the moment I have only "fiddled" with them, and they certainly work,
but until I've tried them full-scale I can't comment on things like bowing and reflection.
pecksniff
thanks for the info, I look forward to seeing the results when you get them setup properly.
thanks for the info, I look forward to seeing the results when you get them setup properly.
Need more work to find pre-anti-reflection coated lens or a place that will coat our lens. I have defected for now and bought a used Prismasonic H600M. I need something I can use immediately without reflections. It is good for now. I am able to fully setup my screen and projector in the room and align everything. It's ok but until I fully do my configuration properly, I won't know the best I can do. I like the total lack of reflections, but I am keen to get to work on my own 4 prism DIY unit but I must have no reflections so either I get these prisms coated or get pre-coated prisms.
Has anybody gone further with the route of anti-refecltion coating of our prisms or has anybody found prisms that are already anti-reflection coated?
Has anybody gone further with the route of anti-refecltion coating of our prisms or has anybody found prisms that are already anti-reflection coated?
OK, I got my wedge lenses the other day, and tested them out.
They seemed to work fine, only issues I have are:
1: color split on rhs
2: slight curve in image horizontaly ( expected & will be rectified with a curve screen)
3: using a 2.35:1 test image, I think it's going to be impossible to have all squares 'square'. looks like you have to make some leeway with having the center squares slightly squished horizontaly and the outside squares slightly elongated, and about 1/3 and 2/3rd position horizontal the squares are square... if you know what I mean.
anyway just threw them in front of projector with both 90deg corners facing the projector seemed to work best for me, first lense about 15deg the second lense about 35deg off parrallel to projector lense.
any one get similar results with angles?
btw the maximum I can go horizontaly is 2850 leaving 200mm either side to walls, so based on that maxiumum for 2.35:1 is 1220, so I will need a 3060x1220 sheet and chop the end off. ( yet to get ).
They seemed to work fine, only issues I have are:
1: color split on rhs
2: slight curve in image horizontaly ( expected & will be rectified with a curve screen)
3: using a 2.35:1 test image, I think it's going to be impossible to have all squares 'square'. looks like you have to make some leeway with having the center squares slightly squished horizontaly and the outside squares slightly elongated, and about 1/3 and 2/3rd position horizontal the squares are square... if you know what I mean.
anyway just threw them in front of projector with both 90deg corners facing the projector seemed to work best for me, first lense about 15deg the second lense about 35deg off parrallel to projector lense.
any one get similar results with angles?
btw the maximum I can go horizontaly is 2850 leaving 200mm either side to walls, so based on that maxiumum for 2.35:1 is 1220, so I will need a 3060x1220 sheet and chop the end off. ( yet to get ).
As a comparison, I am able to get what looks like a more square projection with the H600M. I already want a 4 prism setup. The 2 prisms is good, but the sharpness is not quite up to par. It's like a projector with poor convergence near the sides. Not horrible, just not as sharp as I would like to have in the end. I guess I have some time off so I will research the coating of these DIY lens.
Steve Scherrer said:
Morkys: From my post no. 1327. I havent done it yet, but perhaps you could be the first?
Steve Scherrer said:
Right. I just wonder about these prisms themselves. Are they good enough? Is their geometry good enough? I think it would be wise to research more coating options before diving in. May be a reasonable way to go considering the cost looks not too bad. 4 Prisms may add up though...but it may be worth it.
morkys said:
I am a little confused, and perhaps my original post wasn't clear. But they will take the prisms you supply and provide the antireflective coating on them.
Agreed on trying to find other options, but I don't think you will find much cheaper. I have quotes back from 3, and this one was, by far, the cheapest.