DIY anamorphic lens

[skippy31]

Just to let people know, I built the two glass plate prism with glycerin design that slize proposed and did some initial tests over the weekend.

Seems to work OK, although I did notice some softening of the picture and a slight barrel distortion. I'll run some more tests in the comming days.

I have a BENQ6100 mounted right on axis with with screen due to my room limitations and using the prisms was able to reduce the keystone correction somewhat.

So far so good.

Best Regards,

Skippy31

[skippy31]

Just an update on my lense. Was able to eliminate most of the distortion that I mentioned by adjusting the lense in respect to the projector. There is still a very slight softening of the picture but most of that was corrected when I gave the prisms a final cleaning. Overall very happy with this project.

Best Regards,

Skippy31

[Space Ninja]

hey skippy what do you mean buy "adjusting the lenses in respect to the projector" did you slightly adjust the angles or separate the prisms or something? I also have a benq 6100 and have built my anamorphic lens. It works great but I also have a slight softening of the image and barrel distortion. I can live with it though but just interested in what you did to help alleviate the problems.

To every one else my biggest problem is I have a bad glare problem. If I look at white text on a black background I see a dim copy of the text in the background. I am looking at getting some Denglas, TruVue UltraClear, or the Sandel CrystalView glass. All three have an optical coating like camera lenses that help get rid of the glare. Supposedly people do not even notice that the picture has glass on it with these glass types. I have not got prices but I think it will be cheaper than museum glass. I also bought some of that Vision Clear anti-glare spray for tvs that is supposed to get rid of glare. I am going to try it out and let every one here know if it is any good. I am worried that it will blur the image like the normal acid etched anti reflective glass but I will find out and let every one know. I am very pumped about this thread because I almost bought the retail anamorphic powerbuy lens but now am very glad that I did not because with just a few dollars and time I have gotten very promising results. (sorry if Denglas, TruVue UltraClear, Sandel CrystalView, or Vision Clear have been discussed before but did not see any threads about them so I thought I would share.)

[skippy31]

Hey Ninja,

I found that most of my geometric distortion was caused by adjustments of the lense with respect to the projector. As in twisting the lense left to right. Perhaps barrel distortion was not 100% the right term, but between adjusting keystone on the projector and twisting the lense with respect to the projector I was able to restore the image to be properly rectangular.

The prism angles (with respect to each other) of course determine exactly what aspect ratio you end up with in the end.

Softening well that's another issue....

BTW I'm not having too many issues with reflections, but my projector is mounted behind my wall and any reflections end up on the furnace room ceiling...

Best Regards,

Skippy31

[JudeBarnes]

Has the ideas of using a mirror(s) been proven ineffective to compress or expand an image? I don't see why you'd need two mirrors, seems like you can invert the picture using HTPC software, point the projector the opposite direction and using a single, curved mirror surface in front of it, to push the compressed image back at the screen.

As I understand it, someone said that certain areas of the image would be distorted?

[Alcheringa]

A single mirror doesn't work, except with a pinhole lens i.e. one that only fucuses one ray of light on each point of the screen. Unfortunately, a pinhole lens would make for a very dark projected picture. In the area of illumination of the screen, a projection lens is the opposite of a pinhole lens. It needs to be big to let enough light through to the screen.

In a normal direct projection setup, every point on the screen receives a ray of light from every point on the surface of the projection lens in order to make the picture bright. Focusing the lens ensures this happens.

With a curved mirror interposed between the projection lens and the screen, rays of light from the surface of the lens hit the mirror (on their way to the screen) at different points of its curve. Hence they will be deflected at different angles and, instead of all converging on the desired single point on the far screen, will arrive at a cluster of different points and the image will be blurred.

A curved screen would fix (or at least ameliorate) the problem but would add a whole new level of complication to the anamorphic mechanism.

Throwing the projection lens out of focus to try and "bias" the image before reflecting it off the curved mirror would not work, even in theory, because you're trying to make a flat-field image "fit" a curved mirror and after that a flat screen. The only way of "biasing" the projector image is with an anamorphic lens, which brings us back to the problem we started with.

Catch-22.

[JudeBarnes]

I used to own a 1980-ish front projection television that came out of some bar somewhere, it actually shot the light towards the audience, but a hinged, fold-out cover (which housed the RGB guns) had a mirror on the back side would reflect the light back up at the screen. The screen was CURVED. (Curved in at the corners). This mirror was completely flat but somehow the angle of the mirror must also cause for a need for the curved corners. (perhaps to correct for keystone or other effects of reflecting at that angle?)

[Space Ninja]

Well I finished my second set of anamorphic lenses and I am pretty happy. I ended up getting some truevue ar glass. I was able to get enough truvue glass to make two sets of anamorphic lens for cheaper than it would have cost to make one set of museum glass prisms. It was very hard to find any special glass in my city I actually had to take a two hour tip to get this glass. The only problem it has a slight greenish tint to it but it does not really affect image quality. The good news it did remove my ghosting problem that I had with normal glass. The only problems I have now is I have barrel distortion but for some reason only at the top of the image the bottom seems to be fine. Very strange, has any one else noticed this? And, I also have some chromatic abrasion problems. I am using the distilled water mineral oil combination, would it help to use the distilled water turpentine oil combination? It is not very bad but I do notice it some times especially white on black screens.

I also tried out that Vision Clear anti-glare spray and it worked just like I thought it would. It leaves a slight matt finish to the glass and just makes the image blurry when you project with it. I was able to get a similar effect with a very fine mist of hair spray on the glass. I think the hair spray actually worked better because it was clearer than the vision clear stuff. Either way the vision clear or the hair spray is not good for projection.

I guess I am going to make another set to try to fix the barrel problem and if any one can let me know if turpentine works better than mineral oil I might try that also. Also does any know since my barrel distortion is only at the top if I should just bend the top and not the bottom?

[screw WAF]

Originally posted by Marco T
Anyone try using a dual cylindrical plano convex-plano concave design?

I ordered cylindrical lenses here

http://www.einsteins-emporium.com/sc...tics/sl230.htm

and also some rectangular acrylic prisms from the same company.

Now i wonder if I will be able to fit the light beam from the PJ (Optoma H30) into the 2inch by 2 inch surface. Time will tell.

Hopefully these have a nice surface finish...

If not, my cousin can use them as optics teaching tools.

Marco

Just wondering if this worked out.

Has anyone else used cylindrical lenses successfully?

[JudeBarnes]

Rather than building a very LARGE lense to try and accomplish 2.35 compression on a 4:3 projector... is it possible to build two small ones to compress 1.85 down to 2.35?

What happens to the image if you pass it through 4 total water/oil prisms?