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Discussion Starter · #1 ·
I'd like to cover the hole in the front of my hushbox - where the projector lens shines through, with a piece of glass, in order to "hush" it even more. Quite a bit of noise is coming out of that hole. From research on this forum, it seems like most people are recommending the Edmunds scientific glass.


Unfortunately, they don't make a piece of glass that will fit the window. I need 6"x8", and they only offer 5"x7", and 8"x10" ( here's their site, for anyone interested).


So, I guess I could get the 8x10, and try to cut it myself. Does anyone know how difficult it would be to do that? Could I just take it to the hardware store and ask them to cut it? Or, do normal glass cutters not work with this kind of glass?


Also, how much does it really matter if I use this "special" glass anyway?


Thanks!


- Dave
 

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Dave,


I'm about 99% sure that cutting it with a normal glass cutter will work fine. I believe that there isn't anything particularly special about the glass itself; it's the coating that eliminates reflections. If you want to be 100% sure, just call Edmund - I'm sure they will be able to tell you. They might even do it for you. If you do it yourself or have someone do it for you, make sure that care is taken not to scratch the coating.


You definitely do not want to use normal glass for this purpose. It will reflect a lot of the light back toward the projector. This will cause less light to reach the screen, and will probably cause other problems. Back when the Edmund glass was "discovered" by this forum's members, there were people who were concerned that even it might not be good enough. There was even a discussion about whether the glass should be placed at an angle. I'm using it (without angling it), and it works great. You can hold it up in front of your face, and you don't see your reflection at all. You can tell that it does reflect a small amount of the light at the violet end of the spectrum if you stand with a sunny window behind you - you'll see a dim reflection of the window that looks quite purple.


- Chris
 

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I'm sorry, Chris, but I must differ.


I used a 4"x4" piece of 1/4 inch thick glass from Home Depot. See a picture at my website: www.woodht.homestead.com.


It's been about 9 months, now. I notice no distortion, no reflection, no scatter and especially no diminished light ouput. By the way, I did not mount it at an angle. I am very picky about the image quality. I use AVIA and VE. I am constantly adjusting, tweaking, etc.


One more thought: the glass I used cost about $1.20. It should be easy to go to Home Depot, get a piece and try it out. You can always change it later. You may find that the money for the Edmund glass can be better spent elswhere...



Just my $0.02.


Perry
 

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I agree with Edmund's optical glass. I tried using an aquarium for a hushbox projecting through its glass. Believe me when I say 20% of the image lighting is on the back wall and not on the screen. The screen image is noticeably less bright while through the aquarium ($10 10 gallon kind at Walmart). This was direct projection. I tried to adjust the angle but reflection and light diminishing was apparent. Reflection was so bad that my kids watch the show on the back wall and thought it was "neat". Contrast was down to as light reflected back into DMD panel. I would spend the extra dough and get optical glass. As a side point any one tried a camera filter for optical glass opening for your hushbox. LT150 lens is small enough that a larger filter should do fine and it'll be perfectly round and pretty. Just use a neutral filter and image should be unscathed. If you want you can try different filters to see if it helps or hurts image. Just a thought.
 

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Discussion Starter · #5 ·
Well, I'm inclined to agree with Perry, but I'm going to get the Edmunds glass anyway. I ordered the 8x10 - hopefully it won't be too hard to cut. It was "only" about $40, with shipping. For a piece of glass. Sheesh. I do suspect that I will notice no difference with this, compared to a normal piece of glass, but what the heck. I've already spent a bazillion dollars on everything else, might as well get the best glass, too.


I did try putting a piece of thin glass that I stole from a framed picture in front of the hushbox. The glass was a little dirty, but it was practically invisible. Even when I obscured only half of the projected image, you could barely tell which half had the glass in front of it. Maybe that picture glass was actually highly transmissive, but whatever it was, it seemed fine.


That said, I ordered the Edmunds anyway.


Thanks for all your comments!


- Dave
 

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Non-reflecting glass is used in some picture framing. You could get a piece cut to size at a picture framing shop.


I do not know the specs on Edmund glass. Optical glass is flat and will have no distortion. Optical does not necessarily mean coated, unless it specifies 'coated with anti-reflective material'.
 
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