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Wm Phelps calibration - WOW!!  

post #1 of 18
Thread Starter 
<FONT size="6">!!!!! 700:1 !!!!!</FONT s>

William came to my house last night and calibrated
my G11. The final contrast ratio was a whopping
700:1! The contrast before calibration was 320:1,
which is pretty good for out-of-the-box and explains
why I've been OK with it for the past 10 months. But
now it's more than twice as good. Gamma is virtually
perfect now. I definitely had shading problems before
the calibration; now it's very good (I'll have to watch
a B/W movie sometime).

I'll add more to this post later - I've got a busy work day. But I do want to say that anyone else fortunate enough to live close to Palo Alto should find a time when you can be present when William calibrates your projector. Although there's still a lot that's over my head, it was a great learning experience and it was just plain fun hanging out with him. You're getting more for your money if you can be there.

- Chris
post #2 of 18

That's awesome. William definitely knows his stuff.

Just curious, how low were you able to get the light output for black, and what was your maximum light output? Are you using a GrayHawk, and what size?


post #3 of 18
Good questions, Pat.

Chris, do you remember what your black reading was (in fl)?
post #4 of 18
Black level in foot lamberts wouldn't be of much use, since it's dependent on screen size and throw distance. Lumens directly from the projector is a more meaningful measurement, which I can look up if necessary.

post #5 of 18
William for us uneducated idiots like me, please explain
how you can measure lumens with either a CA-1 or a
mcmahan lightspex, both of which measure in nits or fl only?

I guess i will be a little more specific.

700:1 on a g11 is absolutely impossible.

Since the contrast ratio is a ratio, the units do not
matter. On my g15 the best contrast ratio i can get
is 450:1. And that is measuring the black level about 1
inch off the beginning of the dila panel (measured on
the screen) It cannot get any better than this.

So in any units you choose, i would like to know
the black level and the peak white level. And how
you measured it.

[This message has been edited by kevin gilmore (edited 05-18-2001).]
post #6 of 18

By the way, that is one BIG telescope.
post #7 of 18
I thought it was a Howitzer.
post #8 of 18
Sorry, typed that in a hurry - I meant lux, not lumens. But the point is the same, foot lamberts is not as meaningful a measurement in this case because it is a reflected light measurement and will change depending on screen size, gain, etc. In order to be able to compare measurements we want to use lux or foot candles, a measurement of the light being produced by the projector.

700:1 impossible? 9448/13.5 = 699.8. I'd say that's pretty close to 700. This is only the second projector we've see go this high.


[This message has been edited by wm (edited 05-18-2001).]
post #9 of 18
OK then what is your black level in foot-candles?

what is your peak white level in foot-candles?
post #10 of 18
The McMahan LightSpex is capable of measuring both Luminance/Illuminance as well as Radiance/Irradiance. The instrument may be calibrated for a number of different types of measurments which may be selected via the user display. Measurements may be taken using either the factory supplied cosine receptor or the optional fiber-optic probe which William and I both have. The Lightspex will display W/m2/str, cd/m2, and fL in the Luminance mode in the Illuminance mode it will display data as W/m2, Lux, and fc.

The CA-1 via its emulation software is capable of creating an accurate data file from measurements taken with the LightSpex spectroradiometer. Since it is an emulation of the Lightspex data it can reflect the numbers in whatever mode the LightSpex measured them as.
post #11 of 18
WOW. I think i have died and gone to heaven.

Cliff has finally admitted that with respect to
fixed aperture devices, (like the ca-1, x-rite...)


are all the same once you apply a calibration constant.

half the battle is over. i will now be able to quote
the master himself from now on http://www.avsforum.com/ubb/smile.gif
post #12 of 18

How much you want for the G11?

post #13 of 18

Who cares what the units are? Lux, Lumens, nits, nats. The result is a unitless ratio.

For an on/off measurement as long as you are in the safe operating range of the meter (black level is usually the important one to keep from getting too low), you can measure either incident light or reflected light as long as the room has no other light source. ANSI checkerboard is trickier, but anyone can do an on/off. Turn the lights off. Mesure full white then full black and then divide the two. If the black or white field is uneven, multiple points might have to be taken. I do nine myself in a manner similar to taking a ANSI lumens measurement.

As far as what is or isn't possible with a G11. Richard Martin had significant variance in the units he did. He was only able to achieve 450:1 of Mark Foster's after significant hard work but he had achieved 700:1 on some other peoples units. But as he has stated before, visually the difference between 450:1 and 700:1 isn't as drastic as someone might think.

Wm, Good luck in your efforts.

-Mr. Wigggles

The Mothership is now boarding.

[This message has been edited by MrWigggles (edited 05-19-2001).]
post #14 of 18
Yesterday I re-verified the calibration of the instrument that was used to calibrate Chris' projector. I was able to verify the readings that it gives by comparing it with the McMahan Lightspex. If there are still doubts, I will take the Lightspex to Chris' house and re-measure the contrast ratio, but I am personally satisfied that this is an accurate reading.

As for the telescope, yep, it's big, as refractors go. It's a 180mm (7.1 inch) Astrophysics EDT refractor, three elements of lovingly figured and polished glass. over 350 pounds including the mount. Phenominal views of the planets and the Moon. If you're able, come join us in Yosemite on August 17-18 this year and get a look through it.

post #15 of 18
Thread Starter 
Obviously William was a much better person to answer Pat's
question that I would have been. The one part of the question
that wasn't answered was whether I have a GrayHawk screen.
The answer is no. I have a ~unity gain DaLite screen. I'm
sure it would be great to have one, but it's not in the
budget right now. As has been discussed, the colorimeter
faces toward the projector, not the screen, so the contrast
measurement is independent of the screen type or size. Obviously
the ultimate perceived contrast does depend on the screen.

One interesting thing I wanted to add to this thread is that
William said that he is finding that there is a definite
correlation between the serial number of the projector and
the results he is able to achieve. In general, the newer
the projector, the better the results. I knew that the
older projectors, especially the G10s were much worse out
of the box, but I thought that the factory calibration was
just improving, and that they all had the same potential.
FYI, I bought my projector last June (serial #7510785). I
only have about 200 hours on it though. Maybe the number
of hours is really what is significant, and not the serial
post #16 of 18
I too would like to know the answer to Chris' question.....mine is a G1000...720P capable.....don't know if that makes this later model 1000 or not. Early G10's were not 720P capable.

post #17 of 18
I loved my Astrophysics 7" Starfire. Due to space and wife limitations I had to sell it. Had a very successful e-bay auction a year and a half ago.


post #18 of 18
Even if the telescope talk is slightly off topic, it is interesting that some of us have two hobbies that mirror each other: light cannons for projection AND reception.

I also have a 180mm (F9 TMB) refractor, an 18" F 4.5 Newtonian reflector, along with my (soon) D-ILA and old but contrasty BarcoGraphics400.
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