Lens Masking - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 6 Old 09-12-2015, 01:28 PM - Thread Starter
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Lens Masking

No doubt this is a rookie question, but has anyone ever attempted to build a device that could easily be attached to the [a] pj lens to create blocking of the top/bottom bars when viewing a scope film on a 16:9 screen? Basically the device could be adjusted to create a black shadow top and bottom of the screen without obstructing the main viewable projected screen image.

I'm pretty handy with kydex and assuming complete dark masking can be achieved, I see no major obstacles in making such a device and it could probably be made for under $10. My main concern would be the heat emitting off the lens that might potentially/eventually warp the device.

Just a thought. .. Pros & Cons?

Full Disclosure: I currently don't own a pj, but it has been ordered. This will be my first attempt at building a dedicated HT.

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"Believe none of what you hear and half of what you see" –Tony Soprano

Last edited by los3088; 09-12-2015 at 01:35 PM.
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post #2 of 6 Old 09-12-2015, 04:13 PM - Thread Starter
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Here's a couple of renderings to help explain my concept..:







The lens masking system would consist of three main components, the main body and two bar strips. The main body would be secured to the projector via hook & loop strips. The top and bottom bar strips would attach to the main body via magnetic strips. Adjusting the top and bottom bar strips to obtain the perfect scope mask would be pretty fast and easy once the image is visible on the screen.

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Last edited by los3088; 09-12-2015 at 04:41 PM.
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post #3 of 6 Old 09-13-2015, 05:06 PM
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This won't produce a clean cut off on the image, and instead creates a gradient. See my attached photo. I held up a thick piece of paper right in front of the lens.
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post #4 of 6 Old 09-14-2015, 05:12 AM
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You are not in the focal plane at that point, the "light beams" are called ray pencils at that point. Think of it as every pixel is a big fat tube right there. Where that ray pencil converges to a point it is at the focus location. When you try to mask you are only covering up part of the ray pencil. Translates to each pixel that is being partially interrupted being dimmer on screen. You won't get the sharp line you are thinking you'll get.

Last edited by GetGray; 09-15-2015 at 04:46 AM. Reason: typo
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post #5 of 6 Old 05-21-2019, 01:32 PM
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I don’t know if this would be of interest to anyone here or not, but I found an inexpensive solution that so far I am pretty happy with.

I bought an Optoma UHD50 4K DLP projector in December. I am very pleased with its image. Because of its shorter throw I am getting an approximate 96” wide letterboxed image on my 1.78:1 screen. This is great for wide screen movies (bigger IS better) but using its 3:1 zoom lens I prefer to zoom down to its smallest image for 1.85:1 movies.

The next thing I tried was that using the projector’s modest vertical adjustment I found I could run the image up high enough to mask the top letter box bar. This worked great, but of course made for an even taller gray bar at the bottom of the image. So next I tried holding out a yardstick horizontally to see if I could get a clean enough masking of the bottom letter box bar. It worked.

So I got a slender piece of wood about four foot wide and suspended it horizontally from my ceiling with metal chains. Then I draped pieces of black cloth from the wood. This worked! But only because I have to sit off axis of the projector’s beam because of where the projector had to be placed so I wasn’t blocking its image. This seating arrangement also necessitated adjusting speaker levels in my receiver to balance the sound.

This setup admittedly looks peculiar, but doesn’t bother me because this is a one man movie theater in a small bedroom in our mobile home. My wife prefers watching tv and movies on our 65” tv in our living room. When NOT watching Wide screen film, I simply remove the barrier and go back to watching a smaller image.

If I get tired of this setup, I may try building a very light frame to mask the oversized bottom letter box bar on the bottom of the screen, and then staple black cloth to the front of it. This WOULD make it easier for me to seat myself for a movie!
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post #6 of 6 Old 05-21-2019, 03:43 PM
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Quote:
Originally Posted by William L Carman View Post
I don’t know if this would be of interest to anyone here or not, but I found an inexpensive solution that so far I am pretty happy with.

I bought an Optoma UHD50 4K DLP projector in December. I am very pleased with its image. Because of its shorter throw I am getting an approximate 96” wide letterboxed image on my 1.78:1 screen. This is great for wide screen movies (bigger IS better) but using its 3:1 zoom lens I prefer to zoom down to its smallest image for 1.85:1 movies.

The next thing I tried was that using the projector’s modest vertical adjustment I found I could run the image up high enough to mask the top letter box bar. This worked great, but of course made for an even taller gray bar at the bottom of the image. So next I tried holding out a yardstick horizontally to see if I could get a clean enough masking of the bottom letter box bar. It worked.

So I got a slender piece of wood about four foot wide and suspended it horizontally from my ceiling with metal chains. Then I draped pieces of black cloth from the wood. This worked! But only because I have to sit off axis of the projector’s beam because of where the projector had to be placed so I wasn’t blocking its image. This seating arrangement also necessitated adjusting speaker levels in my receiver to balance the sound.

This setup admittedly looks peculiar, but doesn’t bother me because this is a one man movie theater in a small bedroom in our mobile home. My wife prefers watching tv and movies on our 65” tv in our living room. When NOT watching Wide screen film, I simply remove the barrier and go back to watching a smaller image.

If I get tired of this setup, I may try building a very light frame to mask the oversized bottom letter box bar on the bottom of the screen, and then staple black cloth to the front of it. This WOULD make it easier for me to seat myself for a movie!
I think I would do it the other way around and shift the image down and then mask just the top with the black cloth.

I did something similar for 3 years only I reflected the light off a mirror in the back of the room with the projector pointing backwards. I had a steel frame around the mirror and black plastic masks (4 of them) that I had magnets glued to. This way I had nice 4way masking and nothing hanging down in the room other than the projector.

Bud
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