Projection glass Optiwhite vs Edmund optics? - AVS Forum
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post #1 of 34 Old 10-15-2012, 10:42 AM - Thread Starter
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Hello!
Gonna order some glass for hushbox. Is there any disadvatage choosing Optiwhite glass http://www.pilkington.com/north-america/usa/english/products/bp/bybenefit/specialapplications/optiwhite/default.htm instead of edmund optics glass http://www.edmundoptics.com/optics/windows-diffusers/visible-windows/anti-reflection-ar-coated-high-efficiency-windows/1919 ?
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post #2 of 34 Old 10-15-2012, 11:20 AM
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I definitely wouldn't use the Optiwhite stuff. It has 5 to 8% lower light transmittance and you're paying a lot of money for the light coming out of that projector.

I don't know what the price difference is, but it can't be that substantial as the Edmunds stuff isn't expensive.

* Disclaimer: I'm not a glass expert, but just comparing those numbers makes it seem like an easy one.

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post #3 of 34 Old 10-15-2012, 11:27 AM - Thread Starter
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Originally Posted by AirBenji View Post

I definitely wouldn't use the Optiwhite stuff. It has 5 to 8% lower light transmittance and you're paying a lot of money for the light coming out of that projector.
I don't know what the price difference is, but it can't be that substantial as the Edmunds stuff isn't expensive.
* Disclaimer: I'm not a glass expert, but just comparing those numbers makes it seem like an easy one.
Cool. I was thinking 8mm glass. What do I buy then? Can only find the 3 mm glass?
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post #4 of 34 Old 10-15-2012, 11:37 AM
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Again, I'm by no means an expert, but I'd assume that 3mm is what you want. Good luck!

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post #5 of 34 Old 10-15-2012, 11:43 AM - Thread Starter
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Quote:
Originally Posted by AirBenji View Post

Again, I'm by no means an expert, but I'd assume that 3mm is what you want. Good luck!
I think Optiwhite has 99% light Ra value. Check this out http://www.pilkington.com/resources/glasshandbook2010english.pdf page 196

Can anyone confirm this please?
Greatly appreciated
/maxxy
edit: 3mm is too thin I think, as window will be near highest fan outtake, so glass definately needs to block the sound quite well there. Don't believe less than 6mm would be good.. Atleast what I believe, no expert, this is my first build and it took me 10 days to build this box.
edit2: just looked at the chart again. Maybe the Ra value is not precentage =) No idea..
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post #6 of 34 Old 10-15-2012, 01:03 PM
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In the chart you referenced above, I believe "LT" stands for Light Transmittance. The value is 91%, as confirmed in the Optiwhite brochure. The Edmunds glass allows 96-99% transmittance.

Your call on the glass thickness as I haven't personally used it, but 1) unless you're using a leaf blower as a projector fan, I think you'll be fine with 3mm, and 2) I doubt that an extra 3mm of glass is going to make much difference in sound attenuation. Maybe try two layers of glass with GG in between? Wait a minute........

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post #7 of 34 Old 10-15-2012, 03:12 PM - Thread Starter
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Quote:
Originally Posted by AirBenji View Post

In the chart you referenced above, I believe "LT" stands for Light Transmittance. The value is 91%, as confirmed in the Optiwhite brochure. The Edmunds glass allows 96-99% transmittance.
Your call on the glass thickness as I haven't personally used it, but 1) unless you're using a leaf blower as a projector fan, I think you'll be fine with 3mm, and 2) I doubt that an extra 3mm of glass is going to make much difference in sound attenuation. Maybe try two layers of glass with GG in between? Wait a minute........
hahah
Alright. Actually tried less than 2mm glass from poster glass and it blocked sound ok, so 3 mm just might do the trick after all.

Thanks Benji, I'll order the edmund glass.
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post #8 of 34 Old 10-15-2012, 09:57 PM
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I've just picked up some glass for my hushbox from a local picture frame maker. He just gave me a 3mm thick square piece 14cmx14cm that he had as an off cut. It's interesting you mentioned the LT value, as I was wondering if there is a way to test what I have. Guess I should just place it infront of the lens while it's on and see if I can tell any difference.

So what size did you get?


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post #9 of 34 Old 10-16-2012, 03:55 AM - Thread Starter
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the smallest i could get without being too small, the 5x7 inch one.

bought a glass cutter today, hope I wont break the glass when I cut it smaller..! Atleast I think I will cut it, seems quite large. It will be about 4-5 inches from lens though so dunno.
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post #10 of 34 Old 10-16-2012, 04:10 AM
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There is no real advantage to cutting the glass pane smaller ... and that glass will break easily. Do not place the glass directly parallel to the light path....angle the glass. If 3mm doesn't provide enough sound isolation, use two panes, each set at different angles. (comments apply to the Edmunds glass only)

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post #11 of 34 Old 10-16-2012, 04:17 AM - Thread Starter
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Quote:
Originally Posted by Dennis Erskine View Post

There is no real advantage to cutting the glass pane smaller ... and that glass will break easily. Do not place the glass directly parallel to the light path....angle the glass. If 3mm doesn't provide enough sound isolation, use two panes, each set at different angles. (comments apply to the Edmunds glass only)
the reason for cutting smaller is not to make it better, but to make it fit the box better.. Might look wierd with that much glass in the front.
Yeah I've heard about the angle both for 1 piece, and different angles if 2 are used. Dunno which angle is best though for my setup. I'm casting down from tw9000 about 3.5 meters away, and at top edge of screen on 112"screen (using lens shift only).
Don't know if this will affect which angle is best for my 1 piece of glass.
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post #12 of 34 Old 10-16-2012, 12:36 PM
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Typically 7 degrees (min) off parallel to the lens.

What are you most concerned about ... how pretty your projector box is or how pretty your picture is? Just asking.

Before you go cutting the glass, make certain the opening in the projector cabinet doesn't cast a shadow on the screen or cut off some of your picture.

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post #13 of 34 Old 10-16-2012, 02:18 PM - Thread Starter
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Quote:
Originally Posted by Dennis Erskine View Post

Typically 7 degrees (min) off parallel to the lens.
What are you most concerned about ... how pretty your projector box is or how pretty your picture is? Just asking.
Before you go cutting the glass, make certain the opening in the projector cabinet doesn't cast a shadow on the screen or cut off some of your picture.
Both actually. The box will be a big part of livingroom so want it to be pretty. And ofcourse that picture is great aswell. Can't imagine the glass would get less good from cutting it?

What do you mean by cast a shadow on the edmund glass? You mean if the opening from box out to glass is too small so light will hit the edge of the hole of box and cast it on the glass or..?
Don't understand how to make sure no shadow is cast on the glass.
ps. like it is now it is too small on the sides, so the sides are a bit darker than middle of picture lol. But will make em wider once I finish the box.
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post #14 of 34 Old 10-17-2012, 04:02 AM
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I said "cast a shadow on the screen" ... not the glass.

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post #15 of 34 Old 10-17-2012, 06:46 AM - Thread Starter
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Quote:
Originally Posted by Dennis Erskine View Post

I said "cast a shadow on the screen" ... not the glass.
The window glass screen?
How to avoid
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post #16 of 34 Old 10-17-2012, 07:34 AM
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When using the 2 pane method for sound isolation.

1. Does the thickness matter?

2. What is the ideal spacing?

3. What is the ideal angle to offset the panes?


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post #17 of 34 Old 10-17-2012, 09:29 AM
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Dennis is telling you to make sure that the box does not cause any vignetting to the image that is displayed on your screen. To avoid this, the hole in which the projector's light beam is shining through must be large enough to not "clip" any portion of the light beam. In turn, this means the larger the piece of glass, the larger the hole, the less likely to experience vignetting.

-Sean
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post #18 of 34 Old 10-17-2012, 11:47 AM - Thread Starter
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Originally Posted by 230-SEAN View Post

Dennis is telling you to make sure that the box does not cause any vignetting to the image that is displayed on your screen. To avoid this, the hole in which the projector's light beam is shining through must be large enough to not "clip" any portion of the light beam. In turn, this means the larger the piece of glass, the larger the hole, the less likely to experience vignetting.
-Sean
Thanks Sean. Finally a good answer.

I won't place the glass directly in the hole of box though, but thinking of making the whole large enough like you say and then putting the glass into an external frame which i glue onto the box around the box hole.

This should work right
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post #19 of 34 Old 10-17-2012, 12:35 PM
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In either case, whether the glass is in the box or outside the box in it's own frame, You don't want anything obstructing the light coming from the projector. As you get further from the projector lens, the wider the beam of light will be, and subsequently the larger the piece of glass will need to be. I'm not sure if a few inches in either direction will make a difference or not in your case, but it's something to consider. You just have to make sure that the box opening and/or the glass frame is large enough.

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post #20 of 34 Old 10-17-2012, 12:42 PM - Thread Starter
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Originally Posted by J_P_A View Post

In either case, whether the glass is in the box or outside the box in it's own frame, You don't want anything obstructing the light coming from the projector. As you get further from the projector lens, the wider the beam of light will be, and subsequently the larger the piece of glass will need to be. I'm not sure if a few inches in either direction will make a difference or not in your case, but it's something to consider. You just have to make sure that the box opening and/or the glass frame is large enough.
Yeah hokay. Pretty straighyforward then, was gonna do this anyhow. Only thing I'm still not sure of is exact angle of glass. I've stated my setup distances etc, but guess I'll have to experiment then.
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post #21 of 34 Old 10-17-2012, 12:45 PM
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Quote:
Originally Posted by Dennis Erskine View Post

Typically 7 degrees (min) off parallel to the lens............

Quoted from above for a single pane.

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post #22 of 34 Old 10-18-2012, 03:38 AM
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Quote:
I won't place the glass directly in the hole of box though, but thinking of making the whole large enough like you say and then putting the glass into an external frame which i glue onto the box around the box hole.

External frame for the glass .... good idea. Gluing the external frame--bad idea.
You want to be able to remove the frame and glass easily so you can:

1. Clean the glass front and back (finger prints/dust)
2. Easily replace the glass after you break it.
3. Easily get to the front of the anamorphic lens, the slide, and the projector lens for maintenance, adjustment, focus, cleaning, etc.

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post #23 of 34 Old 10-18-2012, 05:49 PM - Thread Starter
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Quote:
Originally Posted by Dennis Erskine View Post

External frame for the glass .... good idea. Gluing the external frame--bad idea.
You want to be able to remove the frame and glass easily so you can:
1. Clean the glass front and back (finger prints/dust)
2. Easily replace the glass after you break it.
3. Easily get to the front of the anamorphic lens, the slide, and the projector lens for maintenance, adjustment, focus, cleaning, etc.
I've sawed my hushbox into 2 pieces using hinges and locks to fasten it. So I just have to open it to get access to both projector and glass frame.
But I understand what you mean so good point for others who read this.

@JPA: I'm talking about optimal angle for my setup. I don't think 7 degrees is best for every setup, but it might do in my case, no idea.
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post #24 of 34 Old 10-18-2012, 10:41 PM
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Quote:
Originally Posted by Dennis Erskine View Post

Typically 7 degrees (min) off parallel to the lens.

Won't the angle be mainly determined by the distance the glass is to the lens?

Only ask as my glass will be fairly closs to the lens, which could possibly reflect back to the lens. Is there an optimal distance to the glass for that 7degrees?


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post #25 of 34 Old 10-19-2012, 12:11 PM - Thread Starter
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Won't the angle be mainly determined by the distance the glass is to the lens?
Only ask as my glass will be fairly closs to the lens, which could possibly reflect back to the lens. Is there an optimal distance to the glass for that 7degrees?
What I'm wondering too. Got the glass today, will make the frame tomorrow for the glass.
My glass will be about 3-4 inches from lens I believe.
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post #26 of 34 Old 10-19-2012, 12:15 PM
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Seems like the angle of incidence for each ray of light would be the same regardless of the distance from the lens (i.e. the light doesn't bend). Only the illuminated area changes?

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post #27 of 34 Old 10-19-2012, 12:50 PM
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Use yur tiggernomertry boys.

 

Assume ray geometry and just make sure the reflected light doesn't reflect back into the lens/projector. 

 

You can calculate the reflected angle from the angle your glass is set and from those two angles and the distance to the glass get any other triangle features you want.  In other words that 1% of reflected light, make sure it reflects back over the top of the lens and not into it.

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post #28 of 34 Old 10-19-2012, 01:44 PM - Thread Starter
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Originally Posted by NicksHitachi View Post

Use yur tiggernomertry boys.

Assume ray geometry and just make sure the reflected light doesn't reflect back into the lens/projector. 

You can calculate the reflected angle from the angle your glass is set and from those two angles and the distance to the glass get any other triangle features you want.  In other words that 1% of reflected light, make sure it reflects back over the top of the lens and not into it.
You mean like this GLASS1.jpg ?

Alternative 2 (red glass) seems wrong to me.. Looks to me like the light will bounce back straight at lens if you angle it 7 degrees or so since image is being cast down?

If so, I might need 30 degrees or something, what do you think?

Perhaps alternative glass 1 (blue glass) angle would be better? Then 7 degrees or so would make sense?

Hmm...
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Option 2 looks better to me since it is closer to 90 degrees and therefore a shorter pathlength through the glass. Im not shure though and to what degree it matters, idk.

I believe the angle needed depends on the distance of the lens from the glass. I could make 1degree miss the lens with enough distance between it and the glass.
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post #30 of 34 Old 10-19-2012, 03:07 PM - Thread Starter
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Quote:
Originally Posted by NicksHitachi View Post

Option 2 looks better to me since it is closer to 90 degrees and therefore a shorter pathlength through the glass. Im not shure though and to what degree it matters, idk.
I believe the angle needed depends on the distance of the lens from the glass. I could make 1degree miss the lens with enough distance between it and the glass.
Hmmm.. Now I'm even more confused.
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