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-   -   Microperf and hotspotting (http://www.avsforum.com/forum/23-screens/19684-microperf-hotspotting.html)

TGroom 05-21-2001 12:13 PM

I don't think you need to worry about hotspotting until you get around 2.0 gain or higher. Of course this opinion is worth exactly what you paid for it. http://www.avsforum.com/ubb/smile.gif

Tim

cwilson 05-21-2001 01:06 PM

Tim:

A good friend of mine out here in California is originally from Wellington, Kansas. Are you familiar with the Gift family? Tom's opinion is generally worth about what you suggested that yours is.

cwilson 05-21-2001 09:14 PM

I'll be buying a screen when our theater gets near completion. It will probably be a microperf screen but since my projector will be a CRT I'm a little concerned about brightness of image. Has anyone had experience with such a screen where your final gain is 1.2 or 1.3 (rather than the 0.85 or so that I believe is the number for standard microperfs)? Is there danger of hotspotting (which I understand is reflection of the CRT guns) in this situation?

jkv 05-22-2001 04:51 AM

I have a Stewart MicroPerf screen with a gain of 2.0 and use a Dwin hd700 projector. I do not have any problems with hot spotting.

TGroom 05-22-2001 06:43 AM

Whoa, that is wierd. No I don't know them. I am not originally from Wellington, we moved there after my wife got a job teaching there. Glad to see that your theatre is almost done, any pics of it? We have to make do for a few years until we can build a dedicated room. As far as the screen goes I think you will be fine with a 1.2 or 3 as JKV suggested. What kind of projector are you going to be using? If you haven't found one yet, there are some great NEC's in the classifieds. Depending on room size you may want to go with an even higher gain screen than 1.3. Give us an update on the progress.

Tim

Don Stewart 05-22-2001 10:00 AM

Micro-perforations reduce the screens light reflectance by 10.2 percent.

Regards,
Don

cwilson 05-22-2001 10:40 AM

Don:

What kind of screen would you recommend for my situation - 9" CRT, probably 110" 16x9, microperf?

cwilson 05-22-2001 09:26 PM

JKV:

Do you know if that 2.0 gain is before or after microperfing? In other words, is it a 2.0 screen that has holes punched in it (and maybe ends up at 1.5), or is it a 2.5 gain (pure guess) that has holes added and ends up at 2.0? My guess is that the amount of hotspotting would have more to do with the higher number.

Tim:

Unfortunately, our theater is a lonnnnnng way from completion. In fact, we are still working on the design with Dennis Erskine. It will be six months or more, and a year is not impossible, before opening night. I'm hoping to get an Electrohome 9" projector from Tim at E-Tech. At some point I will post pictures.

Craig

jkv 05-23-2001 04:23 AM

Quote:
Originally posted by cwilson:
JKV:

Do you know if that 2.0 gain is before or after microperfing? In other words, is it a 2.0 screen that has holes punched in it (and maybe ends up at 1.5), or is it a 2.5 gain (pure guess) that has holes added and ends up at 2.0? My guess is that the amount of hotspotting would have more to do with the higher number.

CWILSON: I'm not really sure how that works, but my guess is (take that for what it is worth!) that the gain listed (2.0) is that of the final product *after* the holes are added (does anyone here know for sure?). You do notice the holes if you get up close, within 5 feet or so; my first row of seats is at 12 feet so I never notice them. The other thing that I did is that the entire wall behind the screen is painted flat black in order to minimize light reflections. The center channel cabinet is black and I removed the speaker grill/cloth from the center before I set it in place. Some people have mentioned that they have noticed that their screen vibrates a bit when the center is very active, but I have yet to see that with my setup. The front of my center is about 8 inches from the back of the screen.

I will say that I was very nervous about getting this screen because of the high gain; many people told me I would have hot spotting and some people told me not to worry about it. I have not had any hot spotting, so I am very pleased with the results. To be honest, I think the reason why I don't have any hot spotting is due to the fact that I am using a CRT with 7" tubes, the dwin hd700. My guess is that if I used a different projector with larger tubes, then I may have ended up with some hot spotting. It just so happens that given the size of my room, this being my first theater that I built and my budget, this combination of screen/projector, not to mention all of the *other* stuff you need to buy, worked out great for me.

KFung 05-23-2001 09:39 PM

As far as I know you pick the type of screen surface you want (1.3 gain, 2.0 gain, etc. under the trade names used by various manufacturers) and then you subtract the light lost through perforating the screen. So a 2.0 gain microperf would have an actual gain of about 1.8 (when you subtract the approx. 10% light loss from perforations).

cwilson,
I've seen a G90 on a 8" wide screen like yours and it produced an amazing picture with a 1.3 gain screen (I don't remember if it was microperfed). The brightness was only 8 ft-lamberts, but it was plenty bright for me! It you're planning on getting a perforated screen, maybe a 1.5 gain screen?

Good Luck,

Kam Fung


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