Using the CA813 light meter to measure your front projector - Page 6 - AVS Forum | Home Theater Discussions And Reviews
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post #151 of 174 Old 01-24-2017, 05:31 AM
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Originally Posted by Javs View Post
This is the meter I have.

https://www.jaycar.com.au/meter-lux-...-case/p/QM1584

I did a whole spectrum of On/Off contrast measurements with it, and its just fine. I got readings I expected with that. Including Auto Iris readings, so it can go very low reliably I am sure.

Doing the contrast measurements I had the meter really close to the lens, and I figured out how to use it, it can go up to 400,000 Nits, I am only hitting 40k nits or so at the max when the meter is super close to the lens, black readings for On/Off were close enough not to bottom out, and not to blow out... It also has different range modes, so I am familiar with cycling those in LUX to get stable readings. It dosnt really flicker as such, I can tell when it settles down a bit but due to the sensitivity of it and the refresh rate in the panels I can see it always tip toeing on a very small range.
Most meters are designed to be most accurate 75% or above in the range selected. Move the meter closer or further back from the lens until closest to 90% range give or take. Leave it there and do all measurements from that point.
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post #152 of 174 Old 01-24-2017, 05:31 AM
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Originally Posted by roxiedog13 View Post
Well, my 813 showed 56,000:1 on the JVC first run .
For my test I set iris in the off / manual 0 position .
That sounds reasonable for Iris at 0. Reducing the iris will increase the contrast significantly, I get well over 100k:1 with my iris at -12 or so.
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post #153 of 174 Old 01-24-2017, 06:21 AM
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Quote:
Originally Posted by stanger89 View Post
I can't find the post, but what I remember reading about measuring ANSI (I think it was from zombie) was that he made a velvet/protostar lined tube so he could "aim" the meter right at the square he wanted to measure, without getting interference from other squares. I also recall something about a velvet covered board with a hole in it for the meter for measuring projector ANSI.

The other thing I remember is that it's incredibly hard to get good, reliable, accurate ANSI measurements.
I remember Darin doing something similar some years ago, including covering the screen with black velvet.

I've not had any problems getting ANSI CR readings in the past at home and with other peoples setups, including through an anamorphic lens, but I've not done that for some time now. Once I've got things back up and running here, I'll dig out my meter and see how things go.

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post #154 of 174 Old 01-24-2017, 06:45 AM
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Originally Posted by Javs View Post
You got 56k:1 in Iris-0 fully open?

That seems very high. Is that maximum throw?

I get 22k:1 minimum throw on my jvc iris wide open, 112k:1 iris -15 minimum throw, and 130k:1 iris -15 max throw.

Also manufacturers and anybody measuring don't change settings for measuring black then change more settings to measure white.

If you lower your iris to -15 in low lamp and measure white then black without touching it you should see 150k:1 or so.
Throw is not significant , the readings are taken at the projector . Do you mean maximum zoom?

I know the iris was manual, iris may have been left in the position it was set, -6 , Will check that out. What is the rest of your settings with the values posted?

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post #155 of 174 Old 01-24-2017, 06:49 AM
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Quote:
Originally Posted by Gary Lightfoot View Post
I remember Darin doing something similar some years ago, including covering the screen with black velvet.

I've not had any problems getting ANSI CR readings in the past at home and with other peoples setups, including through an anamorphic lens, but I've not done that for some time now. Once I've got things back up and running here, I'll dig out my meter and see how things go.
Making a velvet box is probably going to give true ANSI, probably more suited to a Lab it would seem. Great to see maximum potential, going to be hard to duplicate in a home theater . I do have enough velvet to pull it off though, two boxes of it sitting in the closet waiting for some valuable spare time to install . Have to wait until my wife is away certainly. As always better to beg for forgiveness that get permission .

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post #156 of 174 Old 01-24-2017, 06:56 AM
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Originally Posted by stanger89 View Post
That sounds reasonable for Iris at 0. Reducing the iris will increase the contrast significantly, I get well over 100k:1 with my iris at -12 or so.
I think there is only 10% difference between min and max zoom, haven't done this in a while, was your measurements taken at max or minimum and which meter did you use? Will be a few nights before I get another chance to test anything .
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post #157 of 174 Old 01-24-2017, 06:57 AM
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Quote:
Originally Posted by Javs View Post
I 2nd that, would love to know your procedure Zombie. And also how you measure ANSI contrast? I could not get very good readings for ANSI on the JVC no matter what I tried, something must not be right. Do I need to build a velvet blackout box and stick the meter inside it?

I am also really interested to see the disparity between the T10 and the 813.

Curious as to how much my meter could be out.
I suspect the word might be shocked, especially if several were measured. I bet they are all over the place.

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My room is almost complete and covered in black velvet, so will be interesting to see what the room ANSI is vs the pjs ANSI when I get round to measuring.

Years ago when the JVC HD100 was new, I measured the ANSI of that and a Sim2 projector (can't remember which one) in the same room at a dealer friends of mine. Although the room did equalise them out a lot, the Sim2 still had more ANSI, though it wasn't much and you were unlikely to be able to spot the difference generally. Only with things like end credits did you see the JVCs ghosting and streaking and see that the Sim was much better in that regard. The room was giving around 200+:1 ANSI CR IIRC.

My ast room was an attic space with the upper walls and ceiling in Kodak 18% grey - very neutral when reflecting back onto the screen, but the ANSI was only around 50:1. By covering up the walls and ceiling with black felt p to around 5 feet, the ANSI improved to around 150:1, but the speakers were affecting some of the black squares. When the were covered, I was then getting around 200:1. I'd hope this new room will give more than that, though the screen does go right up to the walls.

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post #159 of 174 Old 01-24-2017, 07:17 AM
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Quote:
Originally Posted by stanger89 View Post
That sounds reasonable for Iris at 0. Reducing the iris will increase the contrast significantly, I get well over 100k:1 with my iris at -12 or so.
56k at full open iris sounds high, especially since I know he is not at long throw.

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post #160 of 174 Old 01-24-2017, 07:50 AM
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Quote:
Originally Posted by Mike Garrett View Post
56k at full open iris sounds high, especially since I know he is not at long throw.
I was just going order of magnitude, Cine4home got 43000:1 for an X9000. 56000:1 seemed "in the ballpark", depending on throw and everything.
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post #161 of 174 Old 01-24-2017, 02:37 PM
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Quote:
Originally Posted by roxiedog13 View Post
Throw is not significant , the readings are taken at the projector . Do you mean maximum zoom?

I know the iris was manual, iris may have been left in the position it was set, -6 , Will check that out. What is the rest of your settings with the values posted?
Throw is certainly significant, its the same as zoom yes.

And the iris is very significant too

My settings were calibrated... D6500. Bright and Contrast at zero. Clear black off, enhance off, iris manual.

Here are the complete numbers.

Note HB Means High Bright Colour Temp.

---------------------------------
MIN THROW
---------------------------------
LOW LAMP -10

0% - 48,571:1
1% - 45,945:1
2% - 15,962:1
3% - 6,273:1
4% - 3,238:1

0% Dynamic Iris - 200k:1

48,571:1 LOW LAMP D6500
54,285:1 LOW LAMP / HIGH BRIGHT COLOUR TEMP

-----

LOW LAMP -0

0% - 22,750:1
1% - 22,377:1
2% - 10,073:1
3% - 4,105:1
4% - 2,363:1

22,750:1 LOW LAMP D6500
27,916:1 LOW LAMP / HIGH BRIGHT COLOUR TEMP

-----

LOW LAMP -15

0% - 112,307:1
1% - 73,000:1
2% - 20,277:1
3% - 7,643:1
4% - 3,518:1

112,307:1 LOW LAMP D6500
127,538:1 LOW LAMP / HIGH BRIGHT COLOUR TEMP

------------------
MAX THROW IRIS -15 LOW LAMP
------------------

131,428:1 D6500
149,142:1 HB

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post #162 of 174 Old 01-24-2017, 06:28 PM
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Quote:
Originally Posted by Javs View Post
Throw is certainly significant, its the same as zoom yes.

And the iris is very significant too

My settings were calibrated... D6500. Bright and Contrast at zero. Clear black off, enhance off, iris manual.

Here are the complete numbers.

Note HB Means High Bright Colour Temp.

---------------------------------
MIN THROW
---------------------------------
LOW LAMP -10

0% - 48,571:1
1% - 45,945:1
2% - 15,962:1
3% - 6,273:1
4% - 3,238:1

0% Dynamic Iris - 200k:1

48,571:1 LOW LAMP D6500
54,285:1 LOW LAMP / HIGH BRIGHT COLOUR TEMP

-----

LOW LAMP -0

0% - 22,750:1
1% - 22,377:1
2% - 10,073:1
3% - 4,105:1
4% - 2,363:1

22,750:1 LOW LAMP D6500
27,916:1 LOW LAMP / HIGH BRIGHT COLOUR TEMP

-----

LOW LAMP -15

0% - 112,307:1
1% - 73,000:1
2% - 20,277:1
3% - 7,643:1
4% - 3,518:1

112,307:1 LOW LAMP D6500
127,538:1 LOW LAMP / HIGH BRIGHT COLOUR TEMP

------------------
MAX THROW IRIS -15 LOW LAMP
------------------

131,428:1 D6500
149,142:1 HB

Thanks for the info and feedback, will get around to this in a couple of days. I didn't mean throw is not important , just came out wrong. I'm at the short end of the throw range, it is not a long throw projector to screen. I used max zoom for the first measurement , iris was manual , may have been mid point. Will pay attention next time and compare may results just to ensure all is on par. That's a bit better detail for cross referencing, only thing missing is the instrument . I'm using the 813 for now, probably going to exchange for a Minolta T10. Then again, if within 5% I may just keep it. For tracking purposes this would be fine.


Thanks again


Edit: just looked again. I think there is some confusion going on. Your saying max throw, I thought you meant max throw range. You mean max zoom I assume.


max zoom=max throw and min zoom=min throw . That's where the confusion is going on I believe.

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post #163 of 174 Old 01-24-2017, 06:39 PM
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Quote:
Originally Posted by roxiedog13 View Post
Edit: just looked again. I think there is some confusion going on. Your saying max throw, I thought you meant max throw range. You mean max zoom I assume.

max zoom=max throw and min zoom=min throw . That's where the confusion is going on I believe.
It has always confused me, I think it confused everyone, but what I do know is max throw is when the image is zoomed in a way that the screen would be at the maximum distance from the projector (You zoom the image until it gets smaller basically). And min throw is the closest possible distance from the projector (The image is the largest possible).

I use mine at min throw, which is where most of my measurements are, thats the brighter one, but less contrast, there is one max throw number there which would be the units maximum possible contrast.

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post #164 of 174 Old 01-24-2017, 06:57 PM
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Quote:
Originally Posted by Javs View Post
It has always confused me, I think it confused everyone, but what I do know is max throw is when the image is zoomed in a way that the screen would be at the maximum distance from the projector (You zoom the image until it gets smaller basically). And min throw is the closest possible distance from the projector (The image is the largest possible).

I use mine at min throw, which is where most of my measurements are, thats the brighter one, but less contrast, there is one max throw number there which would be the units maximum possible contrast.

Well, I had the wording backwards then , below would be correct . I understood what is brightest and which is best for contrast , the descriptions have been so intertwined they are confused by many , myself included obviously.


max throw = smaller image = less brightness = most contrast = min zoom


min throw = larger image = maximum brightness= less contrast = max zoom

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post #165 of 174 Old 01-24-2017, 07:00 PM
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Quote:
Originally Posted by roxiedog13 View Post
Well, I had the wording backwards then , below would be correct . I understood what is brightest and which is best for contrast , the descriptions have been so intertwined they are confused by many , myself included obviously.


max throw = smaller image = less brightness = most contrast = min zoom


min throw = larger image = maximum brightness= less contrast = max zoom
I get you, thats my understanding too,

Except when talking about measuring from the lens, max throw will both be the brightest and the highest contrast

If you are talking about your screen, since its actually further away then the brightness will be less at max throw.

A lot of people refer to max zoom as the opposite though, so thats why I just talk throw since its very difficult to get confused on that terminology.

Its all quite perplexing!

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post #166 of 174 Old 01-24-2017, 07:16 PM
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Quote:
Originally Posted by Javs View Post
I get you, thats my understanding too,

Except when talking about measuring from the lens, max throw will both be the brightest and the highest contrast

If you are talking about your screen, since its actually further away then the brightness will be less at max throw.

A lot of people refer to max zoom as the opposite though, so thats why I just talk throw since its very difficult to get confused on that terminology.

Its all quite perplexing!

I take measurements at the lens, for the 813 being less sensitive at the low range it is recommended for more accurate results 0-ire .


Now that I have the terminology worked out there won't be confusion .


Thanks

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post #167 of 174 Old 02-20-2017, 04:24 PM
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I have an AEMC CA813 light meter that has worked well. I've had it for several years now though, which made me wonder if it was still accurate. I was going to get it calibrated, but that's not cheap, so I ordered a Sper Scientific 840020 Light Meter with a Certificate of Calibration Traceable to N.I.S.T. - not too expensive on Amazon. Anyway, so far, they both read identical numbers. So the good news is my AEMC CA813 is apparently just as accurate as the new light meter with an N.I.S.T. certificate !

So far I really like the Sper - cheaper than an AEMC CA813 too.

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http://www.sperdirect.com/light-mete...c-296-prd1.htm
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post #168 of 174 Old 02-21-2017, 04:45 AM
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I may have to try that. I was measuring things and either my screen gain is way less than 1, or my Dr Meter 1330B is way off. Over the course of calibrating recently my Dr Meter would read like 50fc, but my i1D3 would read more like 23-25fL....
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post #169 of 174 Old 02-21-2017, 07:59 AM
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Quote:
Originally Posted by stanger89 View Post
I may have to try that. I was measuring things and either my screen gain is way less than 1, or my Dr Meter 1330B is way off. Over the course of calibrating recently my Dr Meter would read like 50fc, but my i1D3 would read more like 23-25fL....
So far it is a great meter, and this Sper Scientific 840020C Light Meter is the least expensive light meter I found with a Certificate of Calibration Traceable to N.I.S.T. ( on Amazon - follow the link ) - which hopefully means it's accurate out of the box. A forum member brought a Dr meter over and it measured higher than my CA813. I'm going to compare the Sper and CA813 readings again tonight.

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post #170 of 174 Old 02-21-2017, 08:57 AM
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So far it is a great meter, and this Sper Scientific 840020C Light Meter...
Every time I see that I read it "Super Scientific"
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post #171 of 174 Old 03-16-2017, 08:48 PM
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So possibly stupid question.

I have a JVC RS420 and a CA811 meter.

I picked up a light stand tripod to strap the meter to. Without moving furniture I can get the meter to within about three feet of the lens (which is probably what I'm doing wrong). The shadow of the meter falls on the center of the screen. The room is fully light controlled other than a few component display panels behind the projector.

I put the meter in FC and take readings. 0 IRE black reads at 0.02 FC and IRE 100 reads 296 FC. This is with no iris (if I set the manual iris to what I normally set it at for 16 ftL I can't get a black reading at all). I'm in low lamp and it has about 250 hours on it. Contrast is -5 as it was clipping with discoloration on the test patterns when set at defaults.

This 'only' gives a contrast ratio of 15k ish to 1 when reviews state as much as 20k:1 is common. But I seem to be running out of headroom for reading much lower black level anyways (I'm somewhat surprised that the meter doesn't go lower than two decimal places).

Will all of this make more sense if I move the furniture and get the meter closer to the lens?
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post #172 of 174 Old 03-17-2017, 05:19 AM
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Originally Posted by AMartin56 View Post
So possibly stupid question.

I have a JVC RS420 and a CA811 meter.

I picked up a light stand tripod to strap the meter to. Without moving furniture I can get the meter to within about three feet of the lens (which is probably what I'm doing wrong). The shadow of the meter falls on the center of the screen. The room is fully light controlled other than a few component display panels behind the projector.

I put the meter in FC and take readings. 0 IRE black reads at 0.02 FC and IRE 100 reads 296 FC. This is with no iris (if I set the manual iris to what I normally set it at for 16 ftL I can't get a black reading at all). I'm in low lamp and it has about 250 hours on it. Contrast is -5 as it was clipping with discoloration on the test patterns when set at defaults.

This 'only' gives a contrast ratio of 15k ish to 1 when reviews state as much as 20k:1 is common. But I seem to be running out of headroom for reading much lower black level anyways (I'm somewhat surprised that the meter doesn't go lower than two decimal places).

Will all of this make more sense if I move the furniture and get the meter closer to the lens?
Closest you can go to the lens the better with the AEMC 811. You want to test the projector not the accuracy of the meter so closest to the lens the better. Only time you want a reading at the screen is for ANSI .

I can get closer with the T-10, the AEMC 813 I have needs to be back a bit more, probably 12 inches .You'll also get better accuracy taking FC at the high range ( around 90% max value) and this is where you
want your meter to be. Take the low IRE in lux which is more accurate and convert. That is how I remember, may be reversed.

Between my new T-10 and the AEMC813 I have less than a year old I measured both the JVC and Sony. The AEMC 813 is within +- 3% and that's only assuming the T-10 more accurate. I normally take three separate readings anyway
and average as both with vary a little, even the T-10.

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I can't find the post, but what I remember reading about measuring ANSI (I think it was from zombie) was that he made a velvet/protostar lined tube so he could "aim" the meter right at the square he wanted to measure, without getting interference from other squares. I also recall something about a velvet covered board with a hole in it for the meter for measuring projector ANSI.

The other thing I remember is that it's incredibly hard to get good, reliable, accurate ANSI measurements.
Possibly this one? http://www.avsforum.com/forum/24-dig...l#post40254954

I was reasonable successful with this technique, but next time, I would build a complete black velvet lined box with only a lens opening on one end, and a small square hole on the other.
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I've had a lot of questions recently about using a light meter to measure lumens, ftL, on/off CR and ANSI CR so I'm putting together this basic tutorial. I hope others with experience will chime in and add their tips and techniques that have worked great for them as well.

Note that the following is a depiction of how I use the meter and what works for me. Others techniques I'm sure can be used as well, which may even be better. So don't take this information as definitive, but rather just to give you some ideas. I'm rather new to this meter so it would be great to hear the feedback from others.

Also I'll talk about specific measurements I got with my Ruby at 525 hours on the bulb and using near max throw. For reference I have a 106" diag Firehawk with 1.3 gain.

OK, let's get started...

What is the AEMC CA813?
The AEMC CA813 is a light meter that can be used to measure light output from your pj in foot candles (fc) and lux. It is a popular light meter among AVSers because it is accurate, inexpensive (about $165), and convenient to use.

Using the meter to measure lumens
Set the meter to measure in lux with one decimal point of precision. Display a 100 IRE full field pattern. Ideally your pj should be first calibrated to D65. However this is not necessary if you want to know what the max light output is that your pj is capable of regardless of its calibration.

Stand AT THE SCREEN and rest the back of the sensor gently on your screen (or hold it just in front of it), facing the pj lens. You could use a tripod but doing so doesn't allow you to measure exactly at the screen which I prefer.

Because it is a bright reading the number should dial in within a few seconds. Hold the meter still for best results. If it shows 0 and you have a very bright pj try removing the decimal point percision, or you can also measure in fc instead.

In my case I measured 62.3 lux. However to determine lumens you must now factor in the size of the screen. At first I was confused by this. I thought to myself "What does the screen size have to do with anything since I am measuring the light directly from the pj and not off the screen?".

Well the answer of course is that the lens zoom and focus changes the intensity of the light. So as you zoom out and throw a larger picture, the intensity of the light goes down, and vice-versa. The lumen measurement is designed in such a way that, although the screen size factors into the measurement, it provides a result which can be compared apples-to-apples with anyone else's lumens measurements regardless of their screen size (assuming they measured correctly).

OK, next we convert our lux or fc measurement to lumens. The formulas for this are:

lumens = (lux / 10.76) * square feet of screen in FEET (not inches)

or

lumens = fc * square feet of screen

So in my case my 106" diag FH is 33.22 sq. feet. So I had (62.3 / 10.76) * 33.22 which comes out to 192.4 lumens.

Converting lumens to ftL

To convert your lumens to ftL use this formula:
ftL = lumens * screen gain / (area of screen in sq. feet not inches)

So in my case I was getting 192.4 * 1.3 gain / 33.22 = 7.53ftL

Just a side note: I considered the picture I was getting from my Ruby to be quite bright and punchy, so I was SHOCKED to determine I was only getting 7.5ftL. This taught me an important lesson, because previously I was under the impression that I "had to have" at least 12 ftL to be satisfied. Your preference may be different so you really need to get a sense for yourself what is acceptable. It may also have been the super high 20,200:1 CR I was getting that helped the perceived brightness to be much higher than I would have thought.

How to measure ON/OFF CR
Unlike the previous measurement for lumens, the measurement for on/off CR should be done very close to the pj lens - say about 12-18 inches. This is because the AEMC will not give you sufficient accuracy at the screen with a 0 IRE measurement, especially if your pj has excellent black levels.

The key here is that you do NOT move the zoom or focus of the pjs lens when taking this measurement. Just move your meter up to the front of the lens. You will also need a tripod for this to get an accurate black level reading. Although it can be done without one, it grows tiring trying to keep the sensor stable enough to get an accurate reading otherwise.

So with your meter now just in front of the pj lens using a tripod, set the meter to measure lux with two decimal points of precision. Display a 0 IRE full field pattern. It will take a while for the sensor to adjust. You'll likely see an initial high reading, and then the meter will start dropping off. Give it some time - it can take up to a minute or two. Eventually it will stop dropping and at that point you have your reading.

In my case for 0 IRE I measured 0.16 lux. [Side note: You cannot compare this black level by itself to that of your own, as it is dependent on many factors such as the distance to the lens and zoom/focus position. ]

Next change to a 100 IRE full field pattern. For this you must switch the meter to measure in fc because it will be very high when measured at the pj (much more so then when measured at the screen previously).

Also important is that you measure the 100 IRE pattern at the same exact position as the 0 IRE pattern. This is why using a tripod is so important.

For my 100 IRE pattern I measured 300 fc. To calculate my contrast ratio I just need to convert the fc to lux. To convert fc to lux just multiply the fc by 10.76391. So in my case 300 fc = 3229.173 lux.

To calculate the on/off CR, simply divide the two. In my case:
3229.173 from 100 IRE measurement / 0.16 from 0 IRE measurement = 20182:1

(In case you are wondering, I am using Darin's iris tweaks for the Ruby which yields substantially greater on/off CR than otherwise out of the box).

How to measure ANSI CR
First just a note - I think technically to measure true "ANSI" CR one must make a number of measurements from various parts of the screen and do averages or something along those lines. I do not do this as I think others do not as well. So its important to note that I do not believe the technique I am explaining here measures real ANSI CR but gives you a comparable measurement.

ANSI CR can be measured both at the pj and at the screen. This is because the 0 IRE block in the checkerboard will be a lot higher than a full 0 IRE pattern which enables you to get a good reading at the screen. Reading at the screen is also important as it takes room reflections and any ambient light into account for what you are actually getting at the screen.

Now onto our measurements. Put up the first checkerboard pattern. Put the tripod in front of the pj, similarly to how you did for the on/off measurement. Except this time you want to move the tripod so the sensor is off center of the screen, and instead it should be centered with a black box on the checkerboard pattern. I use the first black box off center. So look back at the screen and position the sensor so that the shadow from the sensor thrown on the screen is centered in that black box.

With the sensor position, take a reading in lux and note it. Now move to the next checkerboard pattern so the sensor is then centered in a 100 IRE white box. You will likely need to read this in fc. Convert this to lux and note this value. Divide the two. The result is your ANSI CR measurement at the pj. In my case I had:
3864.2 from the 100 IRE checkerbox / 37.5 from the 0 IRE checkerbox = 103 ANSI CR at the pj.

Now, repeat this same process, except measure this AT THE SCREEN. Your ANSI will go down, unless you have a perfect bat cave. In my case my ANSI CR at the screen was 70.9 lux / 0.84 lux = 84.4 ANSI CR at the screen.

An interesting expiriment, which I will soon be doing, it to cover up reflective areas of the room and repeat the ANSI CR measurements at the screen to see how things improve.

As a side note - the AEMC does not come with a tripod mount and I don't think one is available. I made a makeshift one very easily which makes taking the 0 IRE measurements much easier. For this I cut a block of wood so that it fits tightly within the top of the tripod mount (insert in its tray). I then drilled two holes in the top that were just big enough to have the two prongs on the sensor fit in snugly. I then covered the whole thing in black felt.

I then also made a black square of felt and cut a hole in the middle just big enough to fit over the black ring which contains the sensor itself. This blocks the light that would otherwise be reflected back at the pj lens and then back into the meter because otherwise that area is a bright yellow plastic that is highly reflective (surprising they wouldn't have at least made this black). Total time about a half hour.

I know I mentioned it here quite a bit, but again I want to stress the importance of using a tripod mount for all these measurements.

Please feel free to ask any questions and post your own experiences and techniques you use in performing these measurements.

For related reading about determining whether a certain screen type and size will work with a projector you are considering, see Bob's excellent thread "Will this projector/screen work in my room? - A tutorial" here: http://www.avsforum.com/avs-vb/showthread.php?t=753497
Thanks for this, most helpful.

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