Cheap coating opportunity for USA prisms - Page 3

True, but his prisms are just 70mm high. Mine are 140mm high. Both are BK7 with an optic coating...


With the pro lenses, your paying for a much finer finish. Whilst the trophies look smooth to the eye, under magnification they are not that smooth. True optic polishing takes time and costs money - time is money...



Hope it works out for you...

Mark

Cool! I know what next weekend's project will be...

Thanks again for doing this!

Just a quick update: My new prisms have arrived and I am very impressed...

Take a look HERE...

Mark

Hi Richard,

Do you have a report yet on how the new coated prisms worked with your projector?

Randy

Just wanted to say I received my prisms today. I did a quick and dirty setup and all I can say is WOW! I'm watching Star Wars Episode 4 in HD right now. The detail is amazing.

These 5x7 coated prisms are much better than my 4x6 prisms I had back in December (I broke them). I have pretty good focus across the screen and minimal CA (my projector is 18' from the screen). Geometry is pretty good as well. You can really only see the 'defects' when viewing test patterns.

When I first arranged my prisms I had reflections all over the place. I did some rearranging and I now have very minimal reflections. The credits from the movie CARS is just about perfect. Here is a quick sketch of how my quick setup looks...



Thanks Richard for getting this together for us!

Klemsaba,

Have you built a case yet?

Do you have block out on the ends of the prisms?

Adding these things will only make it even better viewing experience...

And a quick update HERE with BD and my lens at 720P...

Mark

I haven't built a case or blocked off the ends yet. I pulled my projector down from the ceiling and placed everything on a table so I could 'play' with the prisms. I did put the prism cases along the sides to help block any stray light shining on the walls.

One strange observation is my prism orientation seems backwards to what I see other people doing.



Building a case is next weekend's project.

If your drawing is the same as what you have done with your prisms, then you are correct for HE...

Mark

The idea is to minimize reflections. I took black paint (use the black you buy in bottles at your local hobby store instead of the black you can buy at home depot. The black at the hobby store is much more black than home depot), add a bunch of powdered corn starch to it and paint a few coats on the edge of the prisms. You have to be careful, because once it dries, it will scratch easily off, but this provides a very black, inky non-reflective coating to the ends of the prisms.

Thank you Richard I received my prism today all the way up here in Canada. Great packing job, crystals look perfect.

Now my home theatre setup consists of:

1) DIY Prisms
2) uh... better get cracking

I bought the Massillon Plaque 5''x7'' uncoated prisms. They have almost
like a mirror finish and give reflections all over the place and also on the
image. The image quality wasnt bad. I am not sure how the reflections
can be prevented by changing the orientation.

Anyway...I just returned it.

I would like to know if the Crystal Factory prisms are not from the same
manufacturer. Is CF a glass manufacturer or just a distributor.

why would the coated prisms also give out reflections?

isnt the primary purpose of the coating to avoid the reflections?

Just curious.

Mupi,

You've stated uncoated prisms, but did you block off the ends of the prisms as well?

That will greatly reduce stray light, but the coating just make it that much better...

Mark

You want as perfect a surface as possible to get a better image on the screen. The better the prism surface, the more reflections you probably are going to experience, but that is where the the ar coating comes in. I kind of laughed when I read your post, because to eliminate the reflections from the surface, without coating, you have to introduce some kind of abrasion or something to the surface which will seriously influence the quality of the image.

fact is, these prisms (and any prism used in this context) are going to cause reflections. There are three ways to minimize them:
1. Prism orientation. The reflections comes from the way the beams bounce off the surfaces of the prisms. You can reduce the reflections on the screen by getting the right orientation.
2. Black out the edges (see above). Some of the more serious reflections come from light bouncing off the edges, and since this is the only part of the prism you can safely black out, it is recommended to do so.
3. Coat the prisms with antireflective coating. I'm still waiting to hear side-by-side comparisons of the prisms with and without coating.

I would imagine crystal factory prisms are going to give the exact same reflections as the Masillon plaques.

Hi Mark,

What is the best orientation for the prisms if you are making a VC lens?

Randy

I guess the reflections were coming off the main surfaces. So I
just returned them. of course I lost the S&H.

I will wait for the pro lenses to become affordable :-)

Whilst this works, I don't really promote this use, but because I use the same size prisms for both front and rear element with my lens, I can simply turn it around (now becomes a HC) and then lay it on its side (now becomes VC - but have to remove the stand). I have not had any reason to change the angles from their position as a HE lens, as the image looked geometry correct in VC mode.

Some tilt may be needed though...

Mark

I can not speak for you guys, but I can confidently state that the coating makes a difference in that it does further control stray light reflections (but may not totally eliminate them) and IMHO, helps as the blacks look deeper...

Mark

I have spent some more time with the prisms. Mission Impossible 3 was on Sunday in scope! I haven't seen the HD-DVD version, but the movie looked great on Showtime. I was amazed at the image... usually HD movie channels are a macro-blocking mess or are crop happy.

I didn't notice any reflections except during one scene in the movie, but I can't be sure if it was from the prisms or if that was part of the movie. I didn't think about checking without the prisms in place because I was having too much fun watching the movie!

I can say these new prisms have a better uniform focus than my old Mallison 4x6 prisms. I always had a focus issue on one side of the screen (before I broke them). The new prisms are pretty uniform. As expected, there is a slight defocus between prism/no prism setup, but it is very negligible.

Maybe it is just psychological, but I feel like I have a new projector... and I have 1800+ hours on my lamp! Perhaps the simple fact that I'm no longer zooming my image up 33% to fill the screen is why everything seems clearer.

There is a slight color shift though when using the prisms. Perhaps that is from the AR coating? They are not clear with the AR coating. I haven't done any post prism calibrations or checks.

I'm impressed. I just hope I can build a suitable case to hold the prisms.

Too true there. Nothing like full panel rez all the time...


Off axis, mine look slightly tinted...

Mark

Received my prisms, everything looked great, except for the CF boxes, which looked like they ripped apart easily during shipping. Will be a while before I get them set up. Thanks Richard!

Received my prisms also. Thanks again Richard.

Is anyone able to post pictures yet?

Mark

Since these prisms have the coatings on them what is the best way to clean them? I would hate to rub off the coatings.

Optic glass cleaner and cloth is said to be the best and most cost effective way...

Mark

Here are a few shots.

I have a bow across the top (it doesn't seem as extreme as the photo shows) and the left side isn't vertical. I also don't have even stretch across the screen. Focus is pretty uniform across the screen. I just have the prisms sitting on a table with my projector. I'm sure once I build my case and hang it from the ceiling I can correct some of these issues.



Now for some fun shots where you don't notice any of the problems...

....resized straight from the camera


....resized straight from the camera


....resized straight from the camera


....resized and adjusted levels...

WOW very good

Mark