DIY anamorphic lens

[audiobot]

Mark,

I think I agree that accuracy is more easily obtained with discrete parts than with bending. I must admit that I still don't quite understand your drawing. My visualization skills seem to have deteriorated.

Anyway, I am attaching a very crude illustration of the way I think the prisms should be constructed. The two angles, labeled A1 and A2, at the apexes (apices?) of the triangles are those that must be decided in conjunction with the refraction indexes to cancel CA. As I hope can be seen each prism element overall appears as a truncated triangular prism and each individual element is a triangular prism. The deviation of the pair is less than it would be for a single element prism, but the dispersion (CA) is hopefully zero at one wavelength at least. This is of course all theoretical at this point in time. I still don't quite have a handle on exactly what deviation I need to calculate for. This is complicated by the fact that you are looking at and referencing an HE setup and I am trying to think in terms of a VC system.

We'll see,

Michael

[Mark Techer]

Hi Michael,

That drawing looks good and would make a great pass through mode. Remember you also need to alter the angles of the two prisms to bend the light.

The reason I am making it a tube (square profile) is most of my light reflection troubles have come from the ends of the prisms. So by making the ends of the prism to be the end case, means I hopefully have eliminated this. This is one reason why there are 2 different size prisms, I guess...

I have added some detail to the drawing to make it a little easier to understand. Again I am building a 4 prism lens (each prism is given a P and a number) as I feel that it works better (exhibits less CA) than a standard 2 prism lens. Rather than make the prisms adjustable, I have decide that I will simply remove the lens for pass through mode including true 16:9 and 4 x 3...
In my previous posts, I have stated that I prefer the image throught the lens. Therefore I am also considering making a passthrough mode lens to be mounted to the side of the anamorphic lens. That way I switch from strtetch lens to pass through lens, but the image on screen does not change quality...

With the light tests I ran this morning, the square end is going to have to be 150mm (6" - the same size as the ISCO III).

Mark

[audiobot]

Hi Mark,

Yeah, my drawing is pretty poor. I couldn't get the lens to rotate to indicate a more realistic placement. I do see what your pic is now. What are you going to use for the endpieces? Aren't you worried that Murphy will sneak back with the fixed configuration?

I found you can get black acrylic for a few dollars more than clear and I am thinking of using that for the end, top and bottom pieces. What do you think? I thought maybe it could be roughed up a little with sandpaper if it was too gloss.

Michael

[Mark Techer]

Hi Michael,

Well murphy is always a worry, but I have two projectors and two sets of prisms, and experimenting with both have come to the same angles for 33% light stretch. There should be about 2 degrees on the entry side as well, but I figure the whole lens can be turned a little if need be. My main concern is light reflections from in side the box, so I will most take the shine off the Perspex for these parts.

In the end, I don't envision the parts costing more than $20, so if it works, great, and if not, its not a huge loss. Thats part of the fun of DIY.

Black should be OK, but I think you would want to run some fine wet and dry over it first to take off the shine...

I also want to leave the paper on the very ends right till the end, so that ends of the lens are scratch free. The last set of prisms (the 4 prism lens) has some nasty scatches, but when filled, do not show on screen, but it would be better if there were no scratches from the start...

Mark

[audiobot]

Mark,

Any progress on the new build?

I picked up my car yesterday and due to the rather ridiculous size of the bill my toy money is expended for the next month. I did dig around and find a nice piece of 3/4" thick plexi in the apt. I think I will try cutting a couple of pairs of experimental end pieces out of it. I seem to have found a price for anti-reflective coated glass, but have not yet found a local dealer. I was quoted about $65 sq. ft.

The hunt goes on.

Michael

[Mark Techer]

Update.

Yes I should be able to do this fairly in-expensively by supplying the cutting list and then doing the work myself. I just need to finish that plan first...

Mark

[Mark Techer]

I made a jig today out of 16mm MDF. I cut four 15 degree wedges and one 40 degree (I hope that is right) wedge using a drop saw and then placed the pieces on another piece of board to form the jig. I got some 6mm Persex off-cuts from the plastic guy on Friday, so was able to get the spacing between the wedges right.

I'll let the glue dry tonight and see how it goes tomorrow...

Mark

[Bud Bray]

Hi Mark, new member Bud here. Reading with GREAT interest your progress on a 4 prisim lens. Trying to follow but confused on a few points...
Here goes...You're gluing the Persex to MDF? You are using tap water as a medium, do you boil it first to kill the critters lurking. I was wondering how long the lens would stay clear before the water started turning. Or do you just change the water regularly?
Although i haven't begun, I was wondering, do you need anti-reflective glass or will standard do? Or acrylic?
Sorry if these wrer answered before...i read the pages...47.
You've really got me into a new project...I was dreading spending $700US then trying to justify it to "the boss". You've given me hope.
Bud

[Mark Techer]

Hi Bud,

No glueing Perspex to perspex, the MDF is my jig to hold the pieces at the right angles...

Water is a cost effect medium, you could boil it first, but alge only grow when there is light and air. The light from the projector is not enough and the units are sealed so hopefully won't go green. Anyway if they do, it is not hard to change the water...

My prisms are standard Perspex and there is o special anti reflection coating that I am aware of with these. The photos I have attached are real...

It is good that new people are still joining this (now 3+year) thread and glad to help answer any questions you might have.

I am trying to get to the plastics shop this week for the parts I need as I am keen to get this new project underway...

Mark

[Bud Bray]

Did a GOOGLE search for PERSPEX in Canada and I got PLEXI-GLAS at Home Depot. Is this an acceptable substitute or is it not clear enough? Also, is it possible to PM you?
Bud