DIY anamorphic lens - Page 2

hoxford · 21st July 2002, 08:09 PM

I made my first attempt at working on the lens yesterday. It didn't go too well.

I had a very hard time getting clean, straight cuts in the glass. It didn't break well and when I did manage to get something of a straight snap, the edge would be very "wavy".

After finally getting a few pieces that were close to desirable I attempted to glue them up. That didn't go well at all. I just couldn't get it to come together in the right shape. I ended up with epoxy everywhere and a shape that would never work. The result went into the trash.

I know I am clumsy but this was just ridiculous.

I think I'll try something other than the all glass and epoxy method of construction. Since I don't have access to aluminum bending gear, I'm going to search for some kind of small 'L' bracket material to make a frame, then glue the glass into the frame.

tahustvedt · 21st July 2002, 08:44 PM

I made some formers from cardboard which I put between the surfaces of glass while glueing. I also use a lot of clear plastic tape and align the pieces flat on the table on the tape before I glue so that I can just swing the parts together using the tape as hinges.

It should be possible to make a wood frame for the prisms and painting it and then coat it with epoxy-glue thinned with red-spirit.

I started assembly on the failure-prism again today. I doscivered that the glue had released the aluminium frame where the frame wasn't painted, but where the edge of the frame was covered in paint the glue stuck wery well. So I painted the edges today and will glue it together tomorrow.

Tor Arne

acolby · 21st July 2002, 09:46 PM

Tor,

Great work so far!

I made a prototype completely out of lexan for the sides and surfaces of both prisms. This was about a week ago and no leaks yet. For someone who does not have acsess to metal and plate bending press i think the lexan is the way to go for the side pieces. However it does not work well for the light surfaces. Way to reflective. I am going to get some high quality non reflective glass for the finished version.

My observations so far:

My prototype works fairly well. I also have a short throw projector (panasonic 711xu) and the barrell distortion is significant. I haven't tried your outward curvature of one lens surface yet(not sure how to get the proper curvature drawn out and cut)
I also noticed different areas of the projected image were slightly out of focus. will have to see if this improves using better glass and tighter tolerances when mounting the two prisms.

Has anyone tried using mineral oil instead of turpentine?

Adam

hoxford · 21st July 2002, 10:58 PM

Quote:

Originally posted by tahustvedt

I was worried that the lexan wouldn't be able to withstand the turpentine as it is a strong solvent, but after bathing a piece of lexan in red spirit for ten hours I'm confident it will work (I didn't have any turpentine with me at work to test with).

Be careful with the lexan and turpentine. I was thinking of doing that too (oil prism of lexan) and just did a few searches on lexan/polycarbonate/turpentine with somewhat mixed results. One datasheet said that polycarbonate was resistant to turpentine. Several others listed turpentine as possibly destructive. I think I'll stick with glass.

PigPen · 22nd July 2002, 05:21 PM

Mineral oil is the key. It should not attack the lexan. I am using Edmond Scientific Glass which was quite expansive. It seems to have more reflection than I was expecting. I have the basic prisms bonded together and am now tweaking things in. Thanks to Tor for getting things going! Hopefully more AVS people will help contribute as well.

PP

tahustvedt · 22nd July 2002, 05:59 PM

I found a page stating that care should be taken with using turpentine with lexan. I guess soaking the lexan isn't a good idea, then.

When I ask about mineral oil at the pharmacy they have many different kind of oils available. Does anyone know what the appropriate oil is called?

I'm glueing the prism right now and will fill it later this evening. I will make a new prism soon with compensation in only one direction.

I will make some scetches describing why the compensation can give problems.

Tor Arne

tahustvedt · 22nd July 2002, 06:28 PM

I took some pictures of the prism while glueing. I forgot to take a picture of the top brace. Sorry!

Here the flat side has ben glued to the frame. The brace is next.

The brace has been glued to the frame and the correction-surface is setting.

The finished prism prior to filling and painting the outside of the frame. Notice the brace which shapes the peak-side of the corrective surface.

Tor Arne

PigPen · 22nd July 2002, 07:06 PM

Get a light mineral oil. Whatever you do DON'T MIX THEM! They separate. Don't even mix different brands, pick one and stick with the same.

Learned this the hard way.

PP

tahustvedt · 22nd July 2002, 07:17 PM

I'll try to explain to you the main reason why I want to try correcting just the top and the bottom of the picture.

In the first picture you see the prism from the side. The red lines describe how the lexan would be bent if it was corrective. This compensates for the barrel-distortion but it can introduce another problem. Since we won't be able to position the projection beam accurately on the surface of the prism the beam might be closer to the top or bottom of the prism. This would actually change the peak angle of the prism, if the projection beam exits closer to the peak the prism angle will be smaller than it should be and vice versa. The blue and yellow lines shows how the angles closer to each edge are different from ideal (black edges).

Looking at the prism from the side.

In the second picture we see the prism from the top. Correcting just the top and bottom of the picture by curving the lexan according to the red lines in Figure 2 will not be a problem since the lens doesn't change the horisontal width of the picture. It will be easy to center the lens well enough to get an even focus.

Looking at the prism from the top.

If one wants to correct in both directions it would be best to correct in one direction for each surface, and not like I have done with my prisms up untill now. For example bending the front surface by the vertical axis and bending the aft surface by the horisontal axis. I have been correcting the same surface in both directions all the time.

I don't think the focus drift will be as bad when correcting in only one direction, which might be another benefit from going with this design.

Tor Arne

hoxford · 23rd July 2002, 06:56 PM

I'm still working to get a basic prototype built... no fancy curved, geometry correcting prisms for me yet.

I learned the value of oiling my glass cutting tool yesterday. That trick finally allowed me to make clean, straight cuts.

I also picked up some thin sheet metal and made 'end caps' for the oil prism. I measured out the 24 degree angle, added in a bit of room for a flap to bend down around the edges, and cut the metal out with snips. Then I bent the edge down with a vice and hammer to get a nice sharp 90 degree bend. What I ended up with are top and bottom wedge shaped 'cups' to glue the glass into. It made the assembly process much easier.

I'll work on the water prism today.

21st July 2002, 08:44 PM	#12
tahustvedt diyAudio Member Join Date: Jul 2002 Location: Norway	I made some formers from cardboard which I put between the surfaces of glass while glueing. I also use a lot of clear plastic tape and align the pieces flat on the table on the tape before I glue so that I can just swing the parts together using the tape as hinges. It should be possible to make a wood frame for the prisms and painting it and then coat it with epoxy-glue thinned with red-spirit. I started assembly on the failure-prism again today. I doscivered that the glue had released the aluminium frame where the frame wasn't painted, but where the edge of the frame was covered in paint the glue stuck wery well. So I painted the edges today and will glue it together tomorrow. Tor Arne __________________ Website: http://home.c2i.net/ahustvedt

22nd July 2002, 05:59 PM	#16
tahustvedt diyAudio Member Join Date: Jul 2002 Location: Norway	I found a page stating that care should be taken with using turpentine with lexan. I guess soaking the lexan isn't a good idea, then. When I ask about mineral oil at the pharmacy they have many different kind of oils available. Does anyone know what the appropriate oil is called? I'm glueing the prism right now and will fill it later this evening. I will make a new prism soon with compensation in only one direction. I will make some scetches describing why the compensation can give problems. Tor Arne __________________ Website: http://home.c2i.net/ahustvedt

22nd July 2002, 06:28 PM	#17
tahustvedt diyAudio Member Join Date: Jul 2002 Location: Norway	I took some pictures of the prism while glueing. I forgot to take a picture of the top brace. Sorry! Here the flat side has ben glued to the frame. The brace is next. The brace has been glued to the frame and the correction-surface is setting. The finished prism prior to filling and painting the outside of the frame. Notice the brace which shapes the peak-side of the corrective surface. Tor Arne __________________ Website: http://home.c2i.net/ahustvedt

22nd July 2002, 07:17 PM	#19
tahustvedt diyAudio Member Join Date: Jul 2002 Location: Norway	I'll try to explain to you the main reason why I want to try correcting just the top and the bottom of the picture. In the first picture you see the prism from the side. The red lines describe how the lexan would be bent if it was corrective. This compensates for the barrel-distortion but it can introduce another problem. Since we won't be able to position the projection beam accurately on the surface of the prism the beam might be closer to the top or bottom of the prism. This would actually change the peak angle of the prism, if the projection beam exits closer to the peak the prism angle will be smaller than it should be and vice versa. The blue and yellow lines shows how the angles closer to each edge are different from ideal (black edges). Looking at the prism from the side. In the second picture we see the prism from the top. Correcting just the top and bottom of the picture by curving the lexan according to the red lines in Figure 2 will not be a problem since the lens doesn't change the horisontal width of the picture. It will be easy to center the lens well enough to get an even focus. Looking at the prism from the top. If one wants to correct in both directions it would be best to correct in one direction for each surface, and not like I have done with my prisms up untill now. For example bending the front surface by the vertical axis and bending the aft surface by the horisontal axis. I have been correcting the same surface in both directions all the time. I don't think the focus drift will be as bad when correcting in only one direction, which might be another benefit from going with this design. Tor Arne __________________ Website: http://home.c2i.net/ahustvedt

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21st July 2002, 08:09 PM	#11
hoxford diyAudio Member Join Date: Jul 2002 Location: San Diego, CA	I made my first attempt at working on the lens yesterday. It didn't go too well. I had a very hard time getting clean, straight cuts in the glass. It didn't break well and when I did manage to get something of a straight snap, the edge would be very "wavy". After finally getting a few pieces that were close to desirable I attempted to glue them up. That didn't go well at all. I just couldn't get it to come together in the right shape. I ended up with epoxy everywhere and a shape that would never work. The result went into the trash. I know I am clumsy but this was just ridiculous. I think I'll try something other than the all glass and epoxy method of construction. Since I don't have access to aluminum bending gear, I'm going to search for some kind of small 'L' bracket material to make a frame, then glue the glass into the frame.

21st July 2002, 09:46 PM	#13
acolby diyAudio Member Join Date: Jul 2002 Location: dallas, tx	Tor, Great work so far! I made a prototype completely out of lexan for the sides and surfaces of both prisms. This was about a week ago and no leaks yet. For someone who does not have acsess to metal and plate bending press i think the lexan is the way to go for the side pieces. However it does not work well for the light surfaces. Way to reflective. I am going to get some high quality non reflective glass for the finished version. My observations so far: My prototype works fairly well. I also have a short throw projector (panasonic 711xu) and the barrell distortion is significant. I haven't tried your outward curvature of one lens surface yet(not sure how to get the proper curvature drawn out and cut) I also noticed different areas of the projected image were slightly out of focus. will have to see if this improves using better glass and tighter tolerances when mounting the two prisms. Has anyone tried using mineral oil instead of turpentine? Adam

22nd July 2002, 05:21 PM	#15
PigPen diyAudio Member Join Date: Jul 2002 Location: USA	Mineral oil is the key. It should not attack the lexan. I am using Edmond Scientific Glass which was quite expansive. It seems to have more reflection than I was expecting. I have the basic prisms bonded together and am now tweaking things in. Thanks to Tor for getting things going! Hopefully more AVS people will help contribute as well. PP

22nd July 2002, 07:06 PM	#18
PigPen diyAudio Member Join Date: Jul 2002 Location: USA	Get a light mineral oil. Whatever you do DON'T MIX THEM! They separate. Don't even mix different brands, pick one and stick with the same. Learned this the hard way. PP

23rd July 2002, 06:56 PM	#20
hoxford diyAudio Member Join Date: Jul 2002 Location: San Diego, CA	I'm still working to get a basic prototype built... no fancy curved, geometry correcting prisms for me yet. I learned the value of oiling my glass cutting tool yesterday. That trick finally allowed me to make clean, straight cuts. I also picked up some thin sheet metal and made 'end caps' for the oil prism. I measured out the 24 degree angle, added in a bit of room for a flap to bend down around the edges, and cut the metal out with snips. Then I bent the edge down with a vice and hammer to get a nice sharp 90 degree bend. What I ended up with are top and bottom wedge shaped 'cups' to glue the glass into. It made the assembly process much easier. I'll work on the water prism today.

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