DIY anamorphic lens

[Bud Bray]

Man, you've got PATIENCE!

One quick question tho...what about just using the resin to FILL plexi or glass forms?
That way you don't need to worry about the surface texture, just removing the bubbles, which you've already solved. Sort of like the water filled you previously did. Just thought it might be an easier route to go before you start pulling your hair out, or go BROKE (let's hope not).

Just trying to help out any way I can.
Bud

[Mark Techer]

If at first you don't suceed, try, try again (just go broke in the process )

Hi Bud,

I idea with both Perspex and Glass was exactly that - fill them with resin to replace the liquid (water, glyersol, oil and what ever else had been used) with a solid.

As it turns out, this is not as simple as that for a couple of reasons -

1. Different resins behave differently - ie where the latest product pours virtually bubble free and has in most cases set that way.

2. Contraction rates and setting times vary with ambient air temp and the product itself.

The thickness of the prisms also play a part here as you have two very different temps from end to end, where the knife edge (apex) is much cooler than the opposite end (thick end), which gets very hot due to the amount of product, and that fact that it is an exothermic reaction, the heat can not escape.

Building a "hot box" will help level the playing field as it will keep the temp constant for the entire prism.

3. Adhesion to the inside surface will vary as well. I have not had very good results with Perspex of late. All of the latest batches of prisms have crazy cracks on their insides. It might be a reaction between the resin and the Perspex, or as has been suggested, caused by the resin "tearing itself away" as it contracts.

With the glass, the resin simply let go, and whilst it did shrink, the surfaces came out pretty clean. What might work, and is now what I want to try next is to pour the body first, then laminate the glass faces after the main body has set. There is no shrinkage in thin pours, and if the air can be pushed out, the resin "fills" any imperfections on the sufaces. This effect is similar to how water fills and hides scatches on the inside of a fish tank...

This seems to work with left over product that I keep adding to a previous messy job. I had a fualty batch of another product and it went off in the mixing pot before I could degas. What I ended up with is a pot of resin with a rough surface. I have since added small amounts to the rough area, and it seems to strick quite well, but best of all, levels the imperfections...

Mark

[fisher]

Hi Mark,

I have been interested in 2.35:1 projection since first reading the thread in the AVS forum and even more so since finding this thread a couple of weeks ago.

I am very impressed with your work over the past year - great perseverance!

I am experimenting with glass faced moulds and 'standard' casting resin (if it works, I will try to source some really clear casting resin like this http://www.smooth-on.com/PDF/Crystal Clear 200 Series - TB.pdf or possibly one of the optical resins that are as clear as, or clearer than, glass - like CR39).

So far I have made one prism. It has no bubbles and released nicely from the glass with no shrinkage. I am letting it harden for a few days before polishing.

My question to you is: Why do you want to make prisms with glass (or perspex) faces? Am I missing something or wouldn't it be better if they were just solid resin?

Greg

[Mark Techer]

Hi Fisher,

Good to see some one else having a go at this to

My question to you is: Why do you want to make prisms with glass (or perspex) faces? Am I missing something or wouldn't it be better if they were just solid resin?

Basically my thinking is of not having to pollish the faces. The most successful pour to date (whilst I used the wrong resin) came away cleanly from the 6mm glass that I used as a mold. The faces looked smooth, but I feel that they would still need some work to make them "optical" grade. Pollishing takes time and skill...

I have been interested in 2.35:1 projection since first reading the thread in the AVS forum and even more so since finding this thread a couple of weeks ago.

Are you making a HE or VC?

I am very impressed with your work over the past year - great perseverance!

Thank you. I was only discussing it today whilst re-setting my water prisms - WOW, it really has been a year...

I am experimenting with glass faced moulds and 'standard' casting resin (if it works, I will try to source some really clear casting resin like this http://www.smooth-on.com/PDF/Crystal Clear 200 Series - TB.pdf or possibly one of the optical resins that are as clear as, or clearer than, glass - like CR39).

So far I have made one prism. It has no bubbles and released nicely from the glass with no shrinkage. I am letting it harden for a few days before polishing.

Now I have several questions for you...

I couldn't get your link to work - so is the resin you used epoxy or poly?

I want to hear about the molds. Glass at the front and back - what about the sides? Did you use a release agent, or did the resin you used simply not stick to the glass?

You said no shrinkage - did you mix the full amount of hardener?

Did you build a hot box?

How clear is the one prism you have made? Is it like water?

Are there any striations?

Did you find that the resin takes about 36 hours to fully harden?
I found that the acid from my finger prints can affect the surface if not fully set...

Looking forward to a reply soon...

Mark

[fisher]

Hi Mark,

Thanks for the reply, it helps with motivation to have the feedback (translation: gets me off my ****!)

For perspective, I am new to all of this. I haven't made moulds or cast anything before. I have read this thread and struggled through google translations of the project at http://www.homecinema-fr.com/forum/ (see skhattane post 448 this thread). I have also discussed what I wanted to do with the local resin supply companies and they gave me some advice.

My initial aim is to create a 4 prism set. This has two advantages of achromatising and easier-to-make thinner prisms. I will make 4 at 10deg with the 'standard' casting resin. If that is encouraging, I will think about better angles vs refractive index and clearer casting resins.


I'm planning on trialing with VC, but they should be big enough to have a play with HE (fortunately I have a projector with reasonable zoom).

I couldn't get your link to work - so is the resin you used epoxy or poly?

I can't get the link to display correctly (I think the spaces are confusing it). Put www. in front of:
smooth-on.com/PDF/Crystal Clear 200 Series - TB.pdf
However, this wasn't what I used. The product I used was a general purpose (poly I believe) casting resin.

I want to hear about the molds. Glass at the front and back - what about the sides? Did you use a release agent, or did the resin you used simply not stick to the glass?

The sides are made from perspex. I used a release agent called Frekote which is chemical (not PVA or wax based). I am going to try a cast without the release agent on the glass. It did come out smooth but left a film which I am having trouble polishing off (you can only see it if you look along the surface into a light source and probably won't affect the optical properties).

You said no shrinkage - did you mix the full amount of hardener?

I used less catalyst (0.7%) than the 'standard' 1%. The resin people suggested slowing down the cure time to reduce exothermic effects.

Did you build a hot box?

No. In fact the reverse. I kept the mould cold during the initial cure phase. This was done to slow the cure process. This wasn't hard - I poured at 6:00pm and left it in the garage. Night temp in Auckland is 6-8degC at the moment. I post cured it (in front of a heater at around 30degC for a few hours) after removing from the mould 2 days after the pour.

How clear is the one prism you have made? Is it like water?

It is pretty clear - looks like glass. The manufacturer can't give me a clarity (or refractive index) for it. However, I used this as it was easliy available and cheap to prove (hopefully) the concept. As above, if it works I will try to find some really clear product

As a sidebar, I'm not too worried about light loss. I have used a ND filter to reduce black level in my current setup. My projection priorities in order are contrast, black level, colour then resolution. However, what I don't know is if a less than clear prism will blur or distort the image somehow.

Are there any striations?

I can't see any optical distortion when looking through the prism (apart from the compression and colour fringing), i.e. no visible swirls or striation.

Did you find that the resin takes about 36 hours to fully harden?

I released from the mould after 2 days and it was sticky on the sides (I didn't touch the faces but assume they were the same).
It was fine straight after the post cure.

Greg

[Mark Techer]

Hello Greg,

Thanks for the reply, it helps with motivation to have the feedback (translation: gets me off my ****!)

Totally agreed. I wish I had joined this thread back in 2002 when it was really active...

My initial aim is to create a 4 prism set. This has two advantages of achromatising and easier-to-make thinner prisms. I will make 4 at 10deg with the 'standard' casting resin. If that is encouraging, I will think about better angles vs refractive index and clearer casting resins.

I too am working with 10 degrees. I honestly don't think that any specific angle must be followed. My water prisms are two 30 degree prisms, but having seen actual Prismasonic product, I choose to make my resin casts 10degrees which turn out to be much thinner.

Out of all that one I have made so far, I have a few that work, but most are not clear enough to use for front projection due to either striations (worked out that slow curing times reduced this), bubbles (mixing and pouring technique affect this and I even bought a vacuum chamber), or crazycrack (why I have turned to glass for molds)...

The sides are made from perspex. I used a release agent called Frekote which is chemical (not PVA or wax based). I am going to try a cast without the release agent on the glass. It did come out smooth but left a film which I am having trouble polishing off (you can only see it if you look along the surface into a light source and probably won't affect the optical properties).

Well that is interesting becuase the surfboard finish resin I used lats time also (contains wax) left the same result you describe...

No. In fact the reverse. I kept the mould cold during the initial cure phase. This was done to slow the cure process. This wasn't hard - I poured at 6:00pm and left it in the garage. Night temp in Auckland is 6-8degC at the moment. I post cured it (in front of a heater at around 30degC for a few hours) after removing from the mould 2 days after the pour.

The night temps here are 10 to 12 now, so might give this another go...

It is pretty clear - looks like glass. The manufacturer can't give me a clarity (or refractive index) for it. However, I used this as it was easliy available and cheap to prove (hopefully) the concept. As above, if it works I will try to find some really clear product

I'll be interested to hear the results. The local suppliers here seem to only have one "clear casting and embedding" resin, which I have already trialed and think works well...

I can't see any optical distortion when looking through the prism (apart from the compression and colour fringing), i.e. no visible swirls or striation.

That is really good news. Sound like you have had success with this project...

I released from the mould after 2 days and it was sticky on the sides (I didn't touch the faces but assume they were the same).

I like the idea of the "post cure" and will try that next time. Can you post a photo? How long before you can cast your next prism?

You have just given me a boost of confidence, so I'm off to make another mold

Mark

[fisher]

Hi Mark,

I prepped the mould last night and will pour in the weekend (could be sooner but that is the next time slot )

The mould is made from 5mm and 10mm perspex (or acrylic?). just some strips I had available. I made a pair of triangles from the 5mm and CA (superglue) it to another 5mm rectangular piece. These were then CA'd to the 10mm base. I took some care with positioning the triangles and ensuring everything else was square. Set squares were used for assembly to minimise building in a warp.



I then place double sided foam tape on the base to seat the glass, install the glass sides, tape the top to hold in place and silicon around the edges.



This is the first prism.



And a closeup



and a view along a face into the light (a 500W builders worklight)



Cheers,
Greg

[Mark Techer]

WOW! That prism looks very good. I can see what your saying about the wax coating on the surface, but that could be simply product related because the prism looks great.

I have made my new mold, and hopefully will buy the resin today and pour either today or tomorrow.

Good work

Mark

[Mark Techer]

Here is some shots of the last resin cast. Note - This is why surfboard resin is no good for this project...



The smaller prism. The corners cracked off due to thermal differences (I guess), and the glass on one side cracked, but not as bad as this...


The glass was OK but the resin cracked on the larger prism. I'm not sure a hot box will prevent this from happening, but I have made another mold (horizontal this time)...



The sides are glass, the base and back are perspex. I have used the hot glue gun to hold the parts in place (using a set square to check the vertical sides) and then used the modeling clay to form a seal...

I will use the "clear casting and embedding resin" and see how it turns out...

Mark

[fisher]

I see what you mean about the surfboard resin! Good luck with the casting resin.

In your post 515 you discuss an optics specialist (from OPSM) who makes prisms out of CR39. Did you, or are you able to, get CR39 from him?

water prisms are two 30 degree prisms, but having seen actual Prismasonic product, I choose to make my resin casts 10degrees which turn out to be much thinner.

What are the prism angles that Prismasonic use and what are they made of?

Greg