What meter to get for contrast measurement? - Home Theater Forum and Systems - HomeTheaterShack.com
 
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post #1 of 10 Old 10-02-11, 09:10 PM Thread Starter
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jarrod1937
 
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What meter to get for contrast measurement?

This question pertains more to screen testing in general, but I am wondering what the best equipment would be to get for measuring contrast? I can easily put together an ansi contrast pattern, but I have no idea when it comes to the meter to use. This will be for measuring the amount of reflected light that hits the screen in a 100% light controlled room, and it's affect on the contrast ratio.
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post #2 of 10 Old 10-02-11, 10:43 PM
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Don
 
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Re: What meter to get for contrast measurement?

Quote:
jarrod1937 wrote: View Post
This question pertains more to screen testing in general, but I am wondering what the best equipment would be to get for measuring contrast? I can easily put together an ansi contrast pattern, but I have no idea when it comes to the meter to use. This will be for measuring the amount of reflected light that hits the screen in a 100% light controlled room, and it's affect on the contrast ratio.
If you were wanting to measure the contrast of your PJ I could recommend an accurate light meter for about $40, but since you need to take a reflective reading off a small area of a screen that changes things. The standard instrument used is a 1° spot meter. Those things aren't cheap so be prepared to spend some coin! A quick check using Froogle shows the Spectra Cine cinespot one-degree spotmeter SC600 going for $2,399.95. Yeah, I don't have one either. There are various brands going for between $600 and $800, and then there is a model I just found today called the Shepherd Polaris Dual 5 Digital Flash Meter that sells for around $250. This meter only has a 5° spot meter. but for the purpose at hand I would think that should be sufficient.

BTW, if you learn the correct procedure you could also accurately measure screen gain.
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post #3 of 10 Old 10-02-11, 10:58 PM
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Steve Mechelke -mech
 
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Re: What meter to get for contrast measurement?

I am going to try and use my Sekonic L758C. That's what I use for gain.
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post #4 of 10 Old 10-03-11, 08:52 AM Thread Starter
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jarrod1937
 
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Re: What meter to get for contrast measurement?

Thanks for the replies. I'll definitely check out those options, though as you probably guessed i'll be skipping those > $1,000 as it's hard to justify such a purchase. I'll research the Shepherd Polaris Dual 5, after all if that will do the job well enough, why pay more.
Harpmaker, what would be the procedure to measure gain? I'm currently in college for electronic engineering, so don't worry, nothing is too nerdy for me!
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post #5 of 10 Old 10-03-11, 09:42 AM
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Steve Mechelke -mech
 
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Re: What meter to get for contrast measurement?

You would measure the reference material (I use a block of magnesium carbonate) and then the screen. Then divide the screen by the reference material to get the gain.

I'm not sure of the Shepherd Polaris Dual 5. I haven't seen what type of reading it will give you when using it. It is a camera meter so it may just give you the proper exposure value for your camera and not lumens, lux, foot candles, foot lamberts, or nits. I'd be wary until you find out for sure. I did notice that Sekonic has a L758DR now which may work. It's a bit cheaper than the L758C that I use - $600+ as opposed to $800+. Pros would use a high end spectrophotmeter, something in the neighborhood of $15K or more, or a Minolta CS-100A, which is in the $7500 range IIRC.
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post #6 of 10 Old 10-03-11, 09:48 AM
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Re: What meter to get for contrast measurement?

That Polaris Dual 5 does look very interesting; I would be looking into it myself, but I've recently had some hefty expenditures and the wallet is going to be pretty thin for a while. I see that Mech beat me to an answer. I believe that the Polaris Dual 5 measures in both lux and fc, but be sure about that before you buy. Here is a link to a PDF for this device, it says the meter can do contrast and luminance readings, but I don't see any place that details that. OK, bad news, here is a link to the devices manual and nothing is mentioned about lux of foot candle readings. Bummer...

Measuring peak screen gain isn't difficult, but it is exacting. You must be able to tilt either the screen sample or the light meter so that you get the highest reading possible. This would be the peak gain which is what everyone means when they use the single word "gain". You must then take a reading from a "perfect diffuse reflector". This can be a number of things, but most doing this type of testing use either a target made from barium sulfate, magnesium carbonate or PTFE (Teflon). This is also called a Unity target because it is considered to have a gain of 1.0. The ratio of the two readings is the peak gain for the screen.

The only light in the room should be the PJ or other light illuminating the screen. If using a PJ for the testing use a 100% or 100 IRE white image.

Peak gain is an interesting number, and the one everyone goes ga ga over, but it only tells you one aspect of the screen. To get a better understanding of the screens attributes you should take readings other than on-axis so you can determine gain at other angles. This is how the viewing cone of a screen is determined, and the "half angle" if the screen has one (all high gain screens do). The half angle is the angle where the measured gain of a screen is one half of it's peak gain.
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post #7 of 10 Old 10-03-11, 07:58 PM Thread Starter
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jarrod1937
 
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Re: What meter to get for contrast measurement?

Excellent, thanks for the info. That will definitely be interesting to calculate. Do you guys by any chance know of any good articles with information like this? The more the better, I'd love to delve deeper into screen design and measurements, but don't really know where to look.
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post #8 of 10 Old 10-03-11, 08:34 PM
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Steve Mechelke -mech
 
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Re: What meter to get for contrast measurement?

Here's a great article on contrast from darinp.

Don't know of anything regarding screen design. But for measurements, we probably are one of the few who do it. Jeff Meier (umr) does some stuff occasionally but he's a fairly busy guy. There are a lot of professional reviewers who do professional screen measures - Doug Blackburn to name one.

It's really fairly simple. You need a spectrophotometer, a spotmeter, software and other miscellaneous hardware. If you zip through a bunch of the threads here you should be able to get a handle on it. Keep in mind that there's a lot of cost involved. I've spent quite a bit on hardware and software since I started - probably somewhere in the neighborhood of $5000. Doug and Jeff (listed above) are probably well over 5X+ that amount. I think most everything needed can probably be acquired for something like $2000 or so though.

There used to be a thriving diy screen community at avs. That's where wbassett, Harpmaker and myself came from. Unfortunately the diy community there has become the personal sales floor for Roland Maurice Boughton. Roland's 'mo' is to pm folks and offer his services for painting screens. He did that with myself. And the moderator (prof55) is the owner of a commercial screen paint company called Liquiscreen. I believe he claims that he sold it... to his son. Since he became the moderator, most everyone left. Don't get me wrong either! Everyone has baggage, including us. One of the things I wish I never would have done was to drive one of the avs members that followed us here away. Such is life though. The few knowledgeable folks left post here rather than there. And the knowledgeable folks who end up using their (avs) advice generally end up here asking how to fix what they've done with avs advice.

Enough of the rambling though. Let us know more specifically what you want to know, and we may be able to point you in the right direction. The last person I recall doing this with started his own screen paint company. Don't know if it's still around though.

Someday we really should write up a history of what happened over there.
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post #9 of 10 Old 10-03-11, 08:39 PM
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Re: What meter to get for contrast measurement?

Quote:
jarrod1937 wrote: View Post
Excellent, thanks for the info. That will definitely be interesting to calculate. Do you guys by any chance know of any good articles with information like this? The more the better, I'd love to delve deeper into screen design and measurements, but don't really know where to look.
This info is on the web, but it is a bit hard to find. I lost my links when my PC crashed last year, but maybe Mech or Bill still have theirs.
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post #10 of 10 Old 10-04-11, 11:32 AM Thread Starter
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jarrod1937
 
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Re: What meter to get for contrast measurement?

Quote:
mechman wrote: View Post
Here's a great article on contrast from darinp.

Don't know of anything regarding screen design. But for measurements, we probably are one of the few who do it. Jeff Meier (umr) does some stuff occasionally but he's a fairly busy guy. There are a lot of professional reviewers who do professional screen measures - Doug Blackburn to name one.

It's really fairly simple. You need a spectrophotometer, a spotmeter, software and other miscellaneous hardware. If you zip through a bunch of the threads here you should be able to get a handle on it. Keep in mind that there's a lot of cost involved. I've spent quite a bit on hardware and software since I started - probably somewhere in the neighborhood of $5000. Doug and Jeff (listed above) are probably well over 5X+ that amount. I think most everything needed can probably be acquired for something like $2000 or so though.
Yeah, I can do that, but only by slowing building up to that level of equipment... To bad we all aren't millionaires! ;-)

Quote:
mechman wrote: View Post
There used to be a thriving diy screen community at avs. That's where wbassett, Harpmaker and myself came from. Unfortunately the diy community there has become the personal sales floor for Roland Maurice Boughton. Roland's 'mo' is to pm folks and offer his services for painting screens. He did that with myself. And the moderator (prof55) is the owner of a commercial screen paint company called Liquiscreen. I believe he claims that he sold it... to his son. Since he became the moderator, most everyone left. Don't get me wrong either! Everyone has baggage, including us. One of the things I wish I never would have done was to drive one of the avs members that followed us here away. Such is life though. The few knowledgeable folks left post here rather than there. And the knowledgeable folks who end up using their (avs) advice generally end up here asking how to fix what they've done with avs advice.

Enough of the rambling though. Let us know more specifically what you want to know, and we may be able to point you in the right direction. The last person I recall doing this with started his own screen paint company. Don't know if it's still around though.

Someday we really should write up a history of what happened over there.
Yeah, I actually also post over at avs as well. There I learned about display calibration and physics surrounding audio and audio calibration/treatments (along with other sources of course). However, I don't know how to answer your question. Basically, I am looking for information that ties together what I already know (display calibration) and the actual science behind the screens that have a direct affect on the calibration and display (like measuring gain). So really, any and all information you have at hand would be nice.
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