Calibrating monitor with Blue Gel?

J

jangej03

Member
Hi,

I had bought a panasonic monitor from eBay that stopped working in the middle of shoot.( So now I think eBay is not that good a source if you want a good reliable monitor.) Anyway, I tried to calibrate the monitor using Rosco #80 Primary blue gel but I don't think it works very well. I was following the proper calibrating procedure from http://www.mediacollege.com/video/test-patterns/colour-bars-smpte.html and http://www.greatdv.com/video/smptebars.htm.

I could not get the correct blue bars as you can get with real blue only switch ( which I checked and compared with using the monitor in DVRack) The Panasonic monitor never showed correct blue bars even with several folds of the #80.

Barry Green and others, I have read in your posts and so many other places that you can use blue get or #47 blue filter to fake blue only switch but I did not work for me. Please throw some more light on it.

Best regards,

J.
 
What sort of lighting were you calibrating the monitor in? It's best to do it in the dark/ a dimly lit setting.
 
The blue filter approach is only valid if only the bleu channel is passed. Phosphors in CRT have slightly ovelapping spectral distributions and depending on the filter properties there are still other colors (mostly green) passed through. This makes the calibration unreliable.
 
what andre is saying makes sense. you could try THX Optimizer blue glasses. They're the right
kind of blue. andre has me thinking about the accuracy of this approach, though...
 
I have tried to calibrate in call kind of lighting conditions. Dimly lit , brightly lit, completely dark. I could never get gel (#88 primary blue) to filter out colors properly. Gree alway creeps in. You can never achieve good calibration with this technique not matter what you use blue get, filter or glasses. In my opinion blue filter/gel technique is a great hoax/myth going around. If you want to calibrate a monitor you MUST have blue only.

Barry Green, I would like to hear your take on this.
 
Frankly, I don't recall ever being in the position of having to use a blue gel. I've always had monitors with the blue-only gun.

Obviously some research is warranted here.
 
You should use a Wratten 47B dark blue filter - Link

I have this DVD and it came with a Wratten 47B filter for setting up my home theater TV.
It's very useful since most home TV's do not have a "blue-only" feature. The DVD has a couple minutes of color bars and walks you through the setup. Of course you would not want to set up your monitor to the DVD but to the camera color bars.
 
A little web searching shows that there's definitely not a consensus on what blue gel to use. John Jackman recommends Rosco #80, Douglas Spotted Eagle recommends Rosco #64, Sirius' DVD says Wratten 47B.

In theory, it sure makes sense that a pure blue gel would work as well as a blue-only gun. I mean, the goal is to limit what reaches your eyes to being only blue. Obviously if the blue you're using isn't "pure" blue, other colors could leak through.

How to determine what is a "pure" blue? Well... hmmm... I guess the way to go would be to try various samples in front of a monitor that has a blue-only gun. Display color bars. View through the gel. Toggle the blue-only gun. When you find a shade of blue that looks indistinguishable whether the blue-only gun is on or off, that's the shade you want.

Somewhere here I've got a Lee jungle book, I'll look through it and see if it has anything appropriate, but I doubt it. Seems like a blue gel like that would be pretty specific.
 
The problem is that phosphor based displays (CRT.Plasma) show peaked spectra specifically with the green peaking near (in) the blue range. A wratten 47B(430nm) is probably better, but a tuned smallband in interference filter would be still better. An example of phosphor spectra (though for low voltage phosphors- high voltage phosphors are simular) can be found here:http://www.ece.ucdavis.edu/~chakhovs/Papers/ref18.html
 
I have ordered another monitor with Blue only. Hopefully that does not go dead on me. I also reached the same conclusion as Barry. One has to use a gel/fiter so that no other color except blue reaches eyes. Also seems like what Andre is saying is true as I could see a hint of green through Rosco#80. One thing is certain that Rosco#80 is NOT the correct gel to be used. Do not know about 47B deep blue fiter as I do not have one. Can someone who has it please run some tests.
 
For multiple DILA / LCD / DLP projectors we commonly use Tiffen's 47B viewing glass to rough-in full-field bars. Again, this is for a by-the-eye quick match of phase across multiple units in the same venue, and not for engineering purposes.

More often than not, we're painting the projectors out of calibration after the fact, but it does serve as a baseline.

Good luck.

e
 
jangej03 said:
Do not know about 47B deep blue fiter as I do not have one. Can someone who has it please run some tests.
Click to expand...
SInce I am having exactly the same problem, I will run out and get a 47B filter and let you know how it worked. You have to wait until the weekend, though...

J.
 
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