DIY anamorphic lens

[hoxford]

I also wanted to share a thought I had on blackening the inside of the oil prism.

The concern is that turpentine will attack any kind of paint used. I was thinking of mixing lampblack (the pigment used to make dark paint) in with the epoxy, then spreading the epoxy over the surface to blacken. If the turpentine attacks the epoxy we're screwed anyway. The other trick would be to roughen the surface of the epoxy to make it more light absorbing.

I haven't tried this yet. That'll be phase two.

[rwhitley]

Arne,

Thanks for your project so far. Printed out your original post from AVS before it got yanked and built my first prototype on July 1st weekend. Amazed at the results.

Now I am working towards #2. I found assembling all of the pieces of the prism pretty hard and a little tedious, figured there must be an easier way. I found a 4" PVC fence post material at Home Depot and had them cut it in a 24 degree wedge and then just glued my acrylic face plates on both faces for my turpentine prism. I will take pictures and post them later. But this was way easier and I trust it not to leak much more. Found a place on the internet that sells even larger square plastic tubing and I am waiting for it to arrive for my water prism.

I am still using lexan for the sufaces until I am sure I have the design that I want. I found this place for non reflective glass www.framingsupply.com . 98% transmission almost no reflection and the pricing looks good. If my square tube idea works I should be able to order the glass faces precut.

I will try mineral oil for the next prototype and let everyone know what I find out (if no one else answers the question first).

Rick

Oh yeah and the if square tube thing works, I am sure it can be ordered in black.

[PigPen]

Tor,

I am having a bit of a focus problem with mine. When I look through it, it is crystal clear. I can arrange the prisms and get a little better focus, but not even close to razor sharp. Did you ever run into such problems and find the solution?

PP

[tahustvedt]

My flat prisms don't give any focus problems that I have noticed, but the corrective prism does give a slight focus change which cannot be corrected completely with the focus-lens of the projector. I thought maybe it was because I used two different materials for the surfaces so I have made a new prism now with lexan on both sides.

The square tubing is a good idea and should make construction much simpler.


Tor Arne

[tahustvedt]

I have moved the projector farther away from the screen and this enables me to reduce the zoom and fit the picture inside my previous smaller lenses. The prism with lexan on both sides didn't seem to induc any more focus-change. I guess it's just the correction that does it, then.

I haven't made any new lenses since my last post, I've been busy with other stuff. I did some thinking though. I think just bending one side (bottom, prism-peak side) of the surface is necessary to give a satisfactory correction. When the lens is angled to give uniform picture-geometry the barrel distortion is only visible at the sides and bottom of the picture. the top is straight. I don't know why, but I guess it's because the top edge is just projected almost straight out of the projector and not at such a dramatic angle like the other edges. Of course, this is when the projector is ceiling-mounted. Table-mounting means it goes the other way round.

If you look at posts made by owner of Panamorph-lenses on AVSforum they say that they have accepted that the lens compresses the bottom of the picture more than the top but I think they're just angling it improperly. They're probably angling it so that the barrel-distortion is equal around all the edges.

I will see what kind of square tubing we have at work that I can use for the new waterprism.

I'm not using the newest lens design now, I'm using the previous one that wasn't painted because the mounting came out better on that one, and now that the projector is not as zoomed out it's big enough too.


BTW.
If you're using flat prisms and don't get perfectly even focus top to bottom it's because of the lens'shift that the lenses give. It's just one of those things we'll have to accept I guess. At least for now. Angling the projector back up will fix the focus but the picture will be distorted.


Tor Arne

[chainsaw]

Hi Guys,

I only found this forum today, I was really the DIY lens project when it got going on AVS and was upset when it was removed. Glad to see the posts have continued.

I have finally got 2 weeks holidays and hope to get a chance at making one of these lenses. Just a couple fo things,

How do I go about determining how big to make the prisms. Do I use the measurements on the german website as a guide for my first prototype ?

I gather the glass is used for the oil prism, and the lexan used for the water prism ?

Tor, I noticed in your pictures one of your prisms is all glass on all sides and on other pictures you have a metal frame on some of your prisms?

Sorry if these questions sound stupid. There is so much scattered info, I am just trying to find a starting point.

FWIW, my projector is a VT540.

[tahustvedt]

No problem.

I make the turpentine-prisms all glass and paint the outside surfaces black after assembly and filling. They are glued together with two-component epoxy-glue. No leaks yet.

I make the waterprisms using aluminium frames to which I glue the two glass-surfaces or lexan surface. I have used epoxy-glue for most of my waterprisms too but most of them have sprung leaks and the prism I made with silicone sealant hasn't leaked so I'm switching to that now. The german website describe the same problem/solution.

I didn't use the dimensions from the german website, only the angles, instead I tried to make the prisms as small as possible. To find out how big the prisms need to be you can hold a piece of paper in front of the projector-lens and see how large an area the projection makes. The surfaces of my waterprism, which is the largest prism, are 100x110mm on the model I'm using now. You may want to make it a little larger than that to be sure the picture can actually fit inside the lens.

I only use lexan for the surface that I need to bend. I did make a prism with lexan on both sides but it turned out to be very flexible and the flat side of the prism didn't turn out completely flat. I recommend you either use glass on both sides or, if you're making a corrective prism, glass on one side and lexan on the other. The corrective prism isn't exactly perfect yet and it's very difficult to get right though. The last one I made turned out distorted.


Tor Arne

[rwhitley]

Chris,

If you are joining the rest of us, how about testing mineral oil instead of turpentive to see if it works?

Rick

[chainsaw]

Tor,

thanks for that. It is starting to become clearer now. Just a couple more things.

You mention that the water prism is the larger of the prisms, how do you determine the ratio of how big it should be compared to the oil prism ? If i hold the paper up in front of my projector, i will base that size on the water prism, is it possible to make the oil prism the same size ?

when you mention you paint the outside surfaces of the oil prism black, do you mean the whole prism ?

Thanks again.

[tahustvedt]

I only paint the underside and left/right sides. The optical surfaces can't be painted or the paint would block the light.

The ratio of how big it is doesn't seem to matter. You can make them as big or as small as you like, but to bring the lens as close as possible to the projector, I made the turpentineprism small. The smaller the turpentineprism is, the shorter the bottom surface will be, and the closer the waterprism will be to the projector.

As rwhitley say, you could try mineral oil instead of the turpentine. I won't guarantee that it works as well as the turpentile as I haven't tested it myself.

I'm not sure if the mineral oil will work with the angles we are using, the light may be refracted sifferently in the mineral oil. I dunno!


Tor Arne