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Newbie Help with lum reading

post #1 of 7
10/8/12 at 12:47pm
Thread Starter 
I am back to trying to calibrate my display. I am going through my first try with CalMan 5 and have a quick question about my setup and proper calibration. Things seem to be off for me so I wanted to check here before moving forward.

First my equipment:
- Panasonic AX100U (front LCD projector with dynamic iris off and light harmonizer off)
- SMX acoustically transparent screen
- Theater room which is completely light controlled and readings taken in the dark at screen
- DVDO Edge
- CalMan5 with i1 Display OEM
- Using HTPC as source with AVS 709 blu-ray for patterns
- Equipment running for 45 minutes prior to starting calibration

Whenever I try to get my first Y reading (luminance), I can not get the reading to measure over 3. While the PJ is old, the bulb only has about 600 hours. I have tried numerous positions to take the measurement without any significant change.

I did try to take a measurement off a plasma display in my house and that worked fine. I did have CalMan 4 and the results were the same.

Any help or idea what I am doing wrong? Should I continue with my calibration regardless of the low reading?

Thanks,
T.Wells
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post #2 of 7
10/8/12 at 1:23pm
How big is the screen?

You may want to consider creating an offset and reading directly from the projector.
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post #3 of 7
10/9/12 at 12:24pm
3 what? cd/m2 or fL?

If your reading is 3 fL, that's REALLY dark. If it is 3 cd/m2 it is unbelievably dark. Assuming 3 fL, you probably won't be able to measure

Is your iris opening settable manually? If so, see how high the readings are if you fully open the iris. Opening and closing the iris won't/shouldn't affect anything about calibration except the peak white level and the black level. But if you start at 3 fL for 100% white, you probably won't be able to measure grayscale steps below 30% or so and 30% might even be dicey re. measurement accuracy (depends on the meter). Measuring the screen then the projector directly (same 100% white pattern for both measurements) allows you to measure light from the projector but apply a correction factor that will account (more or less) for any shift the screen causes even though you are measuring brighter light directly from the projector.

Acoustically transparent screens typically do NOT have the gain the manufacturers claim. If the manufacturer says the gain is 1.0-1.2, it's very likely that the gain you measure at home will be more like 0.8 which is not surprising since "transparent" screens typically "leak" enough light that if you put a solid screen behind the "transparent" screen, you can see enough of the image to make out what the image is on the second/solid screen. A lot of people have too much screen or not enough light from the projector or both. The current SMPTE (Society of Motion Picture Technicians and Engineers) is 16 fL for 100% white with a tolerance of 12-20 fL. But keep in mind that if you start with 16 fL and that's the brightest your projector/screen combo can get with a new lamp, when the lamp is near the end of life, you'll have only 8 fL or so.
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post #4 of 7
10/9/12 at 1:39pm
Quote:
Originally Posted by T.Wells View Post

I
Any help or idea what I am doing wrong? Should I continue with my calibration regardless of the low reading?
Thanks,
T.Wells

Put your meter in front of the screen slightly off center, start at about 1foot from the screen.
Display a 100% white full field pattern and take a continuous reading.
While watching the reading adjust the meter up/down left right closer/farther to try and achieve the highest reading.

If 3 fl is your max you need a new lamp or a projector with more output for you screen.

If this is the case, you could move your projector closer to the screen for the calibration or take the reading directly form the lens with the diffuser on the meter.

Hope this helps!
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post #5 of 7
10/9/12 at 6:53pm
Thread Starter 
Quote:
Originally Posted by sotti View Post

How big is the screen?
You may want to consider creating an offset and reading directly from the projector.

The screen is 120" wide (2.35:1).
Quote:
Originally Posted by Doug Blackburn View Post

3 what? cd/m2 or fL?

Sorry, fL is what I am reading.
Quote:
Originally Posted by airscapes View Post

Put your meter in front of the screen slightly off center, start at about 1foot from the screen.
Display a 100% white full field pattern and take a continuous reading.
...
Hope this helps!

Thanks I will give this a try.


All,

Thanks for the help. I will try to post an update this weekend when I get a chance to attempt some new readings.

-T.Wells
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post #6 of 7
10/12/12 at 6:37pm
Thread Starter 
Okay, time for a quick update.

I did get a chance to try some of the above and here is what I found. My lum (Y) reading (fL) changes dramatically based on the picture mode that I select. I had originally selected Cinema 1 (I always ran that mode anyway) as CalMan 4 instructed me to select the mode which gave the closest value to D65. However, the basic workflow in CalMAN 5 didn't include this reading prior to getting the lum reading.

So, here are the approximate readings based on picture mode:
  • Normal - 16 fL
  • Vivid - 22 fL
  • Cinema1 - 6 fL
  • Cinema2 - 5 fL

So, based on those values, I think I should use the normal picture mode and start calibrating. Does anyone feel differently? Is 16fl too low and should I be considering a new bulb/projector at this point? I was hoping to upgrade the project within the next 2-years so I was hoping I could hold out before sinking money into it.

Thanks for the help.

T.Wells
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post #7 of 7
10/12/12 at 6:50pm
Quote:
Originally Posted by T.Wells View Post

Okay, time for a quick update.
I did get a chance to try some of the above and here is what I found. My lum (Y) reading (fL) changes dramatically based on the picture mode that I select. I had originally selected Cinema 1 (I always ran that mode anyway) as CalMan 4 instructed me to select the mode which gave the closest value to D65. However, the basic workflow in CalMAN 5 didn't include this reading prior to getting the lum reading.
So, here are the approximate readings based on picture mode:
  • Normal - 16 fL
  • Vivid - 22 fL
  • Cinema1 - 6 fL
  • Cinema2 - 5 fL
So, based on those values, I think I should use the normal picture mode and start calibrating. Does anyone feel differently? Is 16fl too low and should I be considering a new bulb/projector at this point? I was hoping to upgrade the project within the next 2-years so I was hoping I could hold out before sinking money into it.
Thanks for the help.
T.Wells

16fL is right at the standard for projection, should get you a terrific image with that much light.
5 or 6 fL might be too little.
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