Formula with best mix of accuracy and gain - Home Theater Forum and Systems - HomeTheaterShack.com

Reply
 
Thread Tools
post #1 of 15 Old 10-29-12, 12:58 PM Thread Starter
Senior Shackster
 
Join Date: Jul 2011
Location: Kirkland, WA
Posts: 100
Formula with best mix of accuracy and gain

I've got a JVC RS20 and I'm finding that I'd like a little more brightness. I only have 500 hours on the lamp, but it seems a bit dim. My screen is a Sintra 120" 2.35:1 screen, but unpainted. I'd like to paint it or do something to it to get more gain, but without sacrificing much color accuracy. What would be best for me?
Silas is offline  
Sponsored Links
Advertisement
 
post #2 of 15 Old 10-29-12, 09:48 PM
Moderator Emeritus
Don
 
Join Date: Oct 2007
Location: Central PA
Posts: 3,772
Re: Formula with best mix of accuracy and gain

Quote:
Silas wrote: View Post
I've got a JVC RS20 and I'm finding that I'd like a little more brightness. I only have 500 hours on the lamp, but it seems a bit dim. My screen is a Sintra 120" 2.35:1 screen, but unpainted. I'd like to paint it or do something to it to get more gain, but without sacrificing much color accuracy. What would be best for me?
How are is the PJ mounted from the screen?

You are going to have problems making a screen that has more gain than unpainted white Sintra without introducing a visible viewing cone and possibly getting other screen artifacts such as image graininess or color shifting with viewing angle. Keep in mind that the gain values stated for DIY screen mixes found elsewhere are not accurate. The same goes for commercial screen mixes.
Harpmaker is offline  
post #3 of 15 Old 10-29-12, 09:51 PM Thread Starter
Senior Shackster
 
Join Date: Jul 2011
Location: Kirkland, WA
Posts: 100
Re: Formula with best mix of accuracy and gain

I'm aware. The projector is currently shelf mounted 16 feet from the screen. I can move the shelf to whatever the optimal height is for high gain formulas.
Silas is offline  
 
post #4 of 15 Old 10-29-12, 11:54 PM
Moderator Emeritus
Don
 
Join Date: Oct 2007
Location: Central PA
Posts: 3,772
Re: Formula with best mix of accuracy and gain

Quote:
Silas wrote: View Post
I'm aware. The projector is currently shelf mounted 16 feet from the screen. I can move the shelf to whatever the optimal height is for high gain formulas.
Did you calibrate your PJ? According to one review they got 722 lumens in Cinema 2 mode and normal lamp (the low power setting on the RS20) which would give you over 20 fc of image brightness on a screen your size with your mounting distance, which means you are probably getting around a 22-26 fL image from the unpainted Sintra. You would have to be wearing sunglasses to call such an image dim. I'm beginning to wonder if something isn't wrong with your PJ. You might give some thought to getting a light meter that reads in fc (foot candles) or lux (it's easy to convert from one to the other). This will tell you EXACTLY what image brightness you are really getting. These meters are quite inexpensive (less than $20 shipped) from Amazon. There meters ARE accurate. I have one of these and it gives me the SAME lux readings as my $400 photographic light meter that measures in lux and fc.

If you really do need to get a high gain screen, the best one for the job is actually a commercial screen (the Da-Lite High Power) that has a gain of 2.4. This is a retroreflective screen so to get the brightest image you would mount the PJ at the same height above the floor as your eyes are when viewing.
Harpmaker is offline  
post #5 of 15 Old 10-30-12, 11:20 AM Thread Starter
Senior Shackster
 
Join Date: Jul 2011
Location: Kirkland, WA
Posts: 100
Re: Formula with best mix of accuracy and gain

Sounds good. I bought the LX1330B on eBay since I had some eBay bucks to burn. I'll take some readings and let you know what they are when I get the unit.

Also, keep in mind those readings that Art got are with a fresh bulb. Mine has seen 500+ hours of use, so it's probably only about 14fL, if even that.
Silas is offline  
post #6 of 15 Old 10-31-12, 06:56 PM
Moderator Emeritus
Don
 
Join Date: Oct 2007
Location: Central PA
Posts: 3,772
Re: Formula with best mix of accuracy and gain

Quote:
Silas wrote: View Post
Sounds good. I bought the LX1330B on eBay since I had some eBay bucks to burn. I'll take some readings and let you know what they are when I get the unit.

Also, keep in mind those readings that Art got are with a fresh bulb. Mine has seen 500+ hours of use, so it's probably only about 14fL, if even that.
Cool. Looking forward to some real numbers instead of the guesstimates we usually have to go by.

BTW, what you want to measure is the amount of light falling on the screen and not the light being reflected from the screen. Place the sensor on the middle of the screen and pointing at the PJ then slowly pivot the sensor up, down, left and right until you get the highest reading.
Harpmaker is offline  
post #7 of 15 Old 11-01-12, 12:16 PM Thread Starter
Senior Shackster
 
Join Date: Jul 2011
Location: Kirkland, WA
Posts: 100
Re: Formula with best mix of accuracy and gain

Ok. When I measure that way, am I projecting a white screen?
Silas is offline  
post #8 of 15 Old 11-01-12, 12:42 PM
HTS Moderator
 
Join Date: Sep 2012
Location: Greece
Posts: 519
Re: Formula with best mix of accuracy and gain

Sure yes!!

A 100 IRE white pattern.
Yiannis1970 is offline  
post #9 of 15 Old 11-08-12, 09:58 PM Thread Starter
Senior Shackster
 
Join Date: Jul 2011
Location: Kirkland, WA
Posts: 100
Re: Formula with best mix of accuracy and gain

I am reading 7.87 foot cancels and 84.8 lux at the screen with a 100ire test image. My 16:9 screen area is 83.5"x47" which equals 27.2 sq. ft. This results in 215 lumens at the screen. What the !? The lamp has 615hrs but it shouldn't be THAT dim. Throw is 15ft and the RS20 iris is at -4. I set it to 0 and its barely brighter so I put it back to get better blacks.
Silas is offline  
post #10 of 15 Old 11-09-12, 04:41 AM
HTS Moderator
 
Join Date: Sep 2012
Location: Greece
Posts: 519
Re: Formula with best mix of accuracy and gain

Quote:
Silas wrote: View Post
I am reading 7.87 foot cancels and 84.8 lux at the screen with a 100ire test image. My 16:9 screen area is 83.5"x47" which equals 27.2 sq. ft. This results in 215 lumens at the screen. What the !? The lamp has 615hrs but it shouldn't be THAT dim. Throw is 15ft and the RS20 iris is at -4. I set it to 0 and its barely brighter so I put it back to get better blacks.
I assume you followed the procedure described in post 6 by Don and took a reading of 84.8 lux from the center of the screen. Ok!!

Your screen is 120'' 2,35 which means 127'' in 16:9 (remember your panels are 16:9 and not 2,35). So, we have an area of 4,44 square meters. Therefore:

84.8 x 4.44 = 376,5 Lumens aka 84.8 : 10.76 = 7,88 FL. That's a pretty low number and you have to stick with a screen gain at least 1. So, any shade of gray is probably out of the question. You need the whiter white that's available.


PS

Your lumens are probably less than 376,5 because usually the projectors are far more brighter at the center than in the edges of the screen. So, if you want really know exactly of how many lumens your pj is capable of, you have to measure up 9 points on the screens and divide by 9 to have the exact number.
Yiannis1970 is offline  
Reply

Bookmarks

Tags
accuracy , formula , gain , mix

Quick Reply
Message:
Options

Register Now




PLEASE COMPLETE ALL REQUIRED FIELDS BELOW... THANKS!

REQUIRED FIELDS ON THIS PAGE
YOU MUST COMPLETE ALL OF THESE

Username
Password
Confirm Password
Email Address
Confirm Email Address
Random Question
Random Question #2




User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
PLEASE READ BELOW PRIOR TO ENTERING AN EMAIL ADDRESS!

ATTENTION!

YOU MUST ACTIVATE YOUR ACCOUNT!

Activation requires you reply to an email we will send you after you register... if you do not reply to this email, you will not be able to view certain areas of the forum or certain images... nor will you be able download software.

AN INVALID EMAIL ADDRESS WILL CAUSE YOUR ACCOUNT TO BE DELETED!

See our banned email list here: Banned Email List

We DO NOT respond to spamcop, boxtrapper and spamblocker emails... please add @hometheatershack DOT com to your whitelist prior to registering or you will get nowhere on your registration.


Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML is not allowed!
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

 


For the best viewing experience please update your browser to Google Chrome