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Using the CA813 light meter to measure your front projector - Page 2

post #31 of 105
3/14/07 at 12:23pm
For the meter, I got mine cheap AND talked them out of a free NIST certification with it. I forget the company but I have the link in the appendix of my DVD's manual. If someone looks it up, feel free to post.
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post #32 of 105
3/14/07 at 12:31pm
Thread Starter 
Quote:
Originally Posted by jasonDono View Post

Thanks for the great info! I just ordered a meter. Any advice on getting the tripod up to the lens of a ceiling mounted projector?

Put a table (such as a folding card table) down, then put the tripod on that. See my post above about preventing reflections from the ceiling.
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post #33 of 105
3/14/07 at 12:32pm
Quote:
Originally Posted by GetGray View Post

For the meter, I got mine cheap AND talked them out of a free NIST certification with it. I forget the company but I have the link in the appendix of my DVD's manual. If someone looks it up, feel free to post.

www.repaircalibration.com
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post #34 of 105
3/14/07 at 12:44pm
Quote:
Originally Posted by lovingdvd View Post

Put a table (such as a folding card table) down, then put the tripod on that. See my post above about preventing reflections from the ceiling.

But how do you actually mount the sensor on the tripod?
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post #35 of 105
3/14/07 at 1:18pm
Thread Starter 
Quote:
Originally Posted by Rob Tomlin View Post

But how do you actually mount the sensor on the tripod?

Ahh, yes. I think I wrote about this briefly in my initial post. Basically I created my own tripod mount out of a block of wood. Cut a rectangular block of wood so that it fits snuggly into the tripod tray. Then wrap the whole thing in black felt or velvet, except for the bottom 1/4 inch or so (so that it fits snuggly in the tripod "tray" still). Drill two holes in the top that are snug enough to hold the 2 progs from the AEMC tightly. There's certainly a more elegant way but this was something I was able to throw together in less than 30 minutes and gets the job done well.

Also as a side note, one thing I do not care for with the AEMC meter is that the light sensor is mounted on a bright yellow piece of plastic which is highly reflective. So what I did there was to take a piece of black velvet and cut a hole just big enough to stick the sensor through it. This covers up the yellow plastic and works out quite nicely.
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post #36 of 105
3/14/07 at 1:42pm
Since finding this thread some months ago I have come to feel it is the single best thread I have ever seen on AVS. The sense of empowerment one has after being able to buy a relatively cheap device and simply perform these measuements as tremendous. Why is this not a sticky?

Now I want to know, is there an analogous thread that tells me what (hopefully) cheap instrument to buy and walks me through a (hopefully) simple procedure to set my greyscale to D65?
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post #37 of 105
3/14/07 at 5:33pm
Quote:
Originally Posted by lovingdvd View Post

Ahh, yes. I think I wrote about this briefly in my initial post. Basically I created my own tripod mount out of a block of wood. Cut a rectangular block of wood so that it fits snuggly into the tripod tray. Then wrap the whole thing in black felt or velvet, except for the bottom 1/4 inch or so (so that it fits snuggly in the tripod "tray" still). Drill two holes in the top that are snug enough to hold the 2 progs from the AEMC tightly. There's certainly a more elegant way but this was something I was able to throw together in less than 30 minutes and gets the job done well.

Also as a side note, one thing I do not care for with the AEMC meter is that the light sensor is mounted on a bright yellow piece of plastic which is highly reflective. So what I did there was to take a piece of black velvet and cut a hole just big enough to stick the sensor through it. This covers up the yellow plastic and works out quite nicely.

Thanks Ric. I'm sure I will figure it out once my meter gets here.
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post #38 of 105
3/15/07 at 1:43am
My light meter has an accuracy of 1 lux, i.e. it won't show anything between 0 and 1. What a bummer
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post #39 of 105
3/15/07 at 7:31am
Thread Starter 
Quote:
Originally Posted by pteittinen View Post

My light meter has an accuracy of 1 lux, i.e. it won't show anything between 0 and 1. What a bummer

What light meter is that?
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post #40 of 105
3/15/07 at 7:45am
Quote:
Originally Posted by lovingdvd View Post

What light meter is that?

It's not the CA813, unfortunately. Didn't pay enough attention to specs when I was ordering this one. I'm getting one with more resolution soonish.
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post #41 of 105
3/20/07 at 10:18pm
I measured the lumens output of my current 720p DLP projector tonight. Note that my bulb has 1808 hours on it (I expect it to pop any time now, but no sense in getting a new one with the RS1 on order).

If anything, my lumens output was higher than I expected. I measured 62.8 lux. My screen is 123" diagonal (aprox 5 by 9). So, 62.8 / 10.76 x 45 = 263 lumens. Note that my Dwin projector is not D65 calibrated.

At 263 lumens I am getting 7.6 foot lamberts at the screen.

Like I said, if anything this is a bit higher than what I thought I might get. My picture is definitely still quite watchable, although it could definitely be brighter.

If the RS1 loses 50% of its brightness, I really need to get at LEAST 600 lumens out of it with a new bulb, or it may not be bright enough for my size screen.

I will also measure on/off contrast later this week. This is where I expect this projector to fall short!
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post #42 of 105
4/2/07 at 5:30pm
What's the advantage of going with the 813 over the cheaper 811?
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post #43 of 105
4/8/07 at 8:17pm
I finally got around to measuring the on/off contrast ratio of my current 720p DLP projector (Dwin TV3).

My fc reading was 553 = 5952.44 lux.

The reading for 0 IRE was 2.61 lux (yes, 2.61....quite high).

Thus, my on/off contrast ratio is 2280:1.

This is pretty close to what I was expecting, if not slightly better (I would have put it right at 2000:1).

Still, with the RS1 I should have more than a 6 fold increase in C/R!
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post #44 of 105
4/16/07 at 12:40am
lovingdvd,

Can you post some pictures of your tripod setup. I think I understand how you have it set up but I would like some confirmation with some photos.

Thanks!
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post #45 of 105
4/16/07 at 6:36am
Thread Starter 
Quote:
Originally Posted by snooktarpon View Post

lovingdvd,

Can you post some pictures of your tripod setup. I think I understand how you have it set up but I would like some confirmation with some photos.

Thanks!

Would be happy to but it may be a while before I have a chance. Its pretty simple actually. Just cut a small block a wood so that it fits snugly into the tripod mount tray that is part of your tripod. Then use the 2 prongs from the CA813 as markers in the wood by pressing them down onto the wood enough to leave little guide marks for a drill. Then find a drill bit size that creates a hole that is tight but will allow the prongs to go in and drill it out. Wrap the block in a dark felt or other such material but leave the bottom part that fits into the tray not wrapped (or it will no longer fit into the tray). That's it.
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post #46 of 105
4/18/07 at 9:35pm
You can use this light meter to perform a very accurate measure of your color decoder accuracy.

I have created and uploaded a zipped Excel spreadsheet for this purpose.

1. Use the Gray field (not the White field) on Avia and measure the light output and enter that figure in the red cell labeled "Measured Reference White."
2. Measure the light output from each of the RGBCYM color fields provided on Avia and enter each of those figures in the red fields labeled "Measured Y."

The results will appear numerically and on the provided chart. Good color decoding should show no more than +-5% error for all colors.

Ensure that the light meter is fixed and stable. A tripod mount is desirable for this purpose.

Use the projector's Color control to raise or lower all values. Some projectors have dedicated color decoding controls for RGB. Ideally, the projector will have a CMS that allows you to adjust the Value of RGBCYM independently.

Enjoy.

 

Color Decoding.zip 4.306640625k . file
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post #47 of 105
4/19/07 at 6:25pm
Quote:
Originally Posted by TomHuffman View Post

You can use this light meter to perform a very accurate measure of your color decoder accuracy.

I have created and uploaded a zipped Excel spreadsheet for this purpose.

1. Use the Gray field (not the White field) on Avia and measure the light output and enter that figure in the red cell labeled "Measured Reference White."
2. Measure the light output from each of the RGBCYM color fields provided on Avia and enter each of those figures in the red fields labeled "Measured Y."

The results will appear numerically and on the provided chart. Good color decoding should show no more than +-5% error for all colors.

Ensure that the light meter is fixed and stable. A tripod mount is desirable for this purpose.

Use the projector's Color control to raise or lower all values. Some projectors have dedicated color decoding controls for RGB. Ideally, the projector will have a CMS that allows you to adjust the Value of RGBCYM independently.

Enjoy.

This is great Tom. I'm going to have to give this a try.

Does this test show basically the same thing that using the color filter with DVE is supposed to indicate (only more accurately)?
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post #48 of 105
4/19/07 at 7:39pm
Quote:
Originally Posted by Rob Tomlin View Post

This is great Tom. I'm going to have to give this a try.

Does this test show basically the same thing that using the color filter with DVE is supposed to indicate (only more accurately)?

Exactly.
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post #49 of 105
4/20/07 at 7:21am
Quote:
Originally Posted by TomHuffman View Post

The results will appear numerically and on the provided chart. Good color decoding should show no more than +-5% error for all colors.

Thanks Tom, Whats in col G?
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post #50 of 105
4/20/07 at 7:36am
Quote:
Originally Posted by GetGray View Post

Thanks Tom, Whats in col G?

Just the numeric difference between expected and measured Y.

BTW, I might have mentioned that this is not only a more accurate way of measuring color decoder performance and the user Color setting than the traditional bars/filters, it also provides a reliable way to measure these parameters on the few displays where the bars/filter approach just doesn't work. There are a few of them out there.
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post #51 of 105
4/20/07 at 11:52pm
Quote:
Originally Posted by TomHuffman View Post

1. Use the Gray field (not the White field) on Avia and measure the light output and enter that figure in the red cell labeled "Measured Reference White."

Tom,

What about using a Gray field from the GetGray disc? Will your application work or will you have to tweak it per the source of the test pattern?

Jim
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post #52 of 105
4/21/07 at 7:35am
The patterns on the GetGray DVD are more accurate than the Avia (consumer version) DVD and would work fine with this measurment. I think what is important is that you use the corresponding gray window pattern. The color window patterns are provided at 75% and 100%. So for example, use the 75% gray and the 75% RGBCYM. The 100% set of patterns should work as well, and would show how the decoder was working for at least those 2 levels. The 1.1 version (current version) DVD has corresponding "gray" patterns at the end of the color window sequences, for just such relative measurments in a convenient place.
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post #53 of 105
4/21/07 at 8:46am
Quote:
Originally Posted by hcsi View Post

Tom,

What about using a Gray field from the GetGray disc? Will your application work or will you have to tweak it per the source of the test pattern?

Jim

Any well-designed test patterns will work. I just used Avia as an example because it's well-known. However, as emphasized above, use 75% white with 75% color or 100% white with 100% color. Don't mix and match.
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post #54 of 105
4/22/07 at 10:31am
Using the CA813 meter to measure my HD1's lightoutput, I'm getting much lower results than most others. How accurate is the CA813? (My contrast readings are also a tad low with approx. 12K:1 at max throw, 14.8:1 at min throw)

I'm getting 273/333 (normal/high) lumens at min zoom, and 397/483 (normal/high) lumens at max zoom. The bulb is at 100 hours.
With that said, the picture isn't very bright, and I believe the lightoutput has dropped considerably since it was new.

My contrast readings also seem to vary a lot. I'm getting the best (highest) results when placing the sensor as close to the lens as possible. Offcourse without moving outside of CA813 dynamic range (up to 200klux). The straylight should be of no importance when the sensor is so close to the lens..... Right?
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post #55 of 105
4/22/07 at 12:52pm
Quote:


Using the CA813 meter to measure my HD1's light output, I'm getting much lower results than most others. How accurate is the CA813?

It is quite accurate. You got an under-performing bulb. It's not that uncommon.
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post #56 of 105
4/22/07 at 1:12pm
anbjornk: That does sound a bit low. I just measured 480 lumens, low lamp, max zoom (i.e., as close to the screen as possible), with 250 hrs on the lamp. (With a CA 813).
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post #57 of 105
4/22/07 at 2:25pm
Quote:


It is quite accurate. You got an under-performing bulb. It's not that uncommon.

Okelidokeli.. A reasonable explanation.

Quote:


anbjornk: That does sound a bit low. I just measured 480 lumens, low lamp, max zoom (i.e., as close to the screen as possible), with 250 hrs on the lamp. (With a CA 813).

Thats not bad after 250 hours...
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post #58 of 105
5/9/07 at 10:29am
I assume there are different procedures for determining performance of the projector itself verses the projector in a particular room. If the masking and such your are talking about eliminates the effects of room reflections, aren't you creating numbers you can't see?
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post #59 of 105
5/12/07 at 10:00am
Can someone tell me how to find a 100 IRE test pattern? The latest Digital Video Essentials has a 100% amplitute pattern (is that the same?).

Also it is not full screen and I assume 'full field' means 'full screen'?
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post #60 of 105
5/12/07 at 10:30am
Quote:
Originally Posted by Ian_Currie View Post

Can someone tell me how to find a 100 IRE test pattern? The latest Digital Video Essentials has a 100% amplitute pattern (is that the same?).

Also it is not full screen and I assume 'full field' means 'full screen'?

They are not literally the same, however many people use them term interchangeably (and often incorrectly). But 100% amplitude does usually = 100IRE. The same isn't always true on teh other end of the scale. Full field = full screen. See link in my sig for one source of the pattern. Also, see appendix in realted documentation for differences in % amplitude vs IRE.
HTH, Scott
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