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Author Topic: Black screen on projection  (Read 3596 times)

Ben Lawrence

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Black screen on projection
« on: February 27, 2009, 04:14:06 pm »

Hi everyone. I have a gig coming up and am looking for a way to have my projector display a black signal until the program material is ready to play off a dvd. Problem is I am not in line of sight in order to take the projector off standby and without signal the screen goes to blue. There is a freeze function but when its on it displays the word freeze on the screen. I am looking for a quick fix to produce a black signal until I am ready to run my dvd. I have a cheap a/b switch but other than that am limited on my resources at this point.

John Birchman, CTS

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Re: Black screen on projection
« Reply #1 on: February 27, 2009, 04:19:40 pm »

Depending on the projector, some of them have a setting in the menu so you can change the background from blue to black when there is no signal present.

What projector do you have?  Maybe we can help you find that if we knew what projector you are using.

John
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John Birchman, CTS
Freelance AV and Stage Technician
JRB Technical
Lake Buena Vista, FL

Ben Lawrence

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Re: Black screen on projection
« Reply #2 on: February 27, 2009, 04:23:27 pm »

Dukane imagepro 8940. It looks like there is a black screen setting but it doesnt appear to do anything.

John Birchman, CTS

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Re: Black screen on projection
« Reply #3 on: February 27, 2009, 04:38:28 pm »

Ok, with that projector it looks like the Screen Blank setting only for using the Blank feature on the remote.

Do you have the remote?  It looks like you may be able to use a stereo mini cable to connect to the projector, depending on the remote you have.

The manual is here, if you need it:

http://www.aboutprojectors.com/pdf/dukane-imagepro-8940-manu al.pdf

Hopefully this is of some help.

John
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John Birchman, CTS
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JRB Technical
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Ben Lawrence

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Re: Black screen on projection
« Reply #4 on: February 27, 2009, 04:40:30 pm »

Thanks I was just reading the manual myself with no luck. I have a remote that does not have a 1/8 connector on it. DOH go figure. Is there any other way to rig this?

John Birchman, CTS

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Re: Black screen on projection
« Reply #5 on: February 27, 2009, 05:31:42 pm »

Only thing that comes to my mind right now; is either you find someone else to be closer to the projector with the remote that you have, or possibly try and find a IR remote extender (radio shack may still have in stores), so that you can use the remote where you are.

Otherwise, possibly burn a loop of black, and have 2 player, and a switch between them.

That's all I have right now.

Good luck!

John
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John Birchman, CTS
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JRB Technical
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Ben Lawrence

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Re: Black screen on projection
« Reply #6 on: February 27, 2009, 05:53:02 pm »

Thank you. I was considering the black loop.

Brad Weber

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Re: Black screen on projection
« Reply #7 on: February 27, 2009, 06:54:50 pm »

I wonder if what you are seeing is the DVD screen when it is is standby.  Are you using a DVD player of a laptop?
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Brad Weber
muse Audio Video

Craig Hauber

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Re: Black screen on projection
« Reply #8 on: February 27, 2009, 11:35:44 pm »

go mechanical!

http://www.wahlberg.dk/video/shutter.htm

(It sits close enough to the lens it acts more like a fade than a wipe)

I've done it with a stagehand and a piece of cardboard too

rear project recommended Smile


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Craig Hauber
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waldo [Casey Williams]

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Re: Black screen on projection
« Reply #9 on: March 02, 2009, 03:25:40 am »

That shutter looks awesome! Not cheap at 225 euros, but probably worth it in saving embarrassment.

One thing I have done, is render a dvd that is black with just a subtle red spot on one corner. That way I know the projector and dvd player are live. However, the contrast ratio of my cheap projector is not so hot, so in situations where I have needed a total black, clients have noticed that there is still light hitting the screen. The shutter would solve that.
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Brad Weber

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Re: Black screen on projection
« Reply #10 on: March 02, 2009, 09:36:12 am »

Unless you also control any ambient light, you are never going to get a black screen.  In fact, except for some cinema and home theater applications, it is unusual to have an image contrast ratio that is really affected by the projector contrast.  In typical applications a good image contrast ratio is 10:1, a fraction of even a 500:1 projector contrast.

I'm not saying that contrast is not a factor to consider just that between various ways to measure the projector contrast  (such as full on/full off versus ANSI checkerboard) and ambient light on the screen, it is often not a significant factor.
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Brad Weber
muse Audio Video

waldo [Casey Williams]

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Re: Black screen on projection
« Reply #11 on: March 03, 2009, 05:43:01 pm »

Brad (or others), maybe you can help educate me...I'm not really a video guy.

I do have total control over all ambient light in my room. (Well, aside from the audience holding up cell phones, or god forbid, lighters.) So my experience has been that when I pull all the lights down for a near-total black, like for a band walk-on, the projector's 'black' is by far the brightest thing in the room.

So here's my question: Looking at two projectors that have the same ratings in terms of lumens -- say, 2500, but different contrast ratios. Projector 1 is 2500 lumens with a contrast ratio of 1000:1. Projector 2 is 2500 lumens with a contrast ratio of 500:1.

Is it not correct to assume the 'black' from projector 2 will be twice as bright as projector 1?

waldo
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Brad Weber

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Re: Black screen on projection
« Reply #12 on: March 04, 2009, 09:09:18 am »

waldo    [Casey Williams

 wrote on Tue, 03 March 2009 17:43]So here's my question: Looking at two projectors that have the same ratings in terms of lumens -- say, 2500, but different contrast ratios. Projector 1 is 2500 lumens with a contrast ratio of 1000:1. Projector 2 is 2500 lumens with a contrast ratio of 500:1.

Is it not correct to assume the 'black' from projector 2 will be twice as bright as projector 1?

Maybe?  If they were both measured the same and set up the same, including black level, then yes.

Contrast in projector terms is an indication of the difference between black and white and not a measurement of the black level.  In theory, if two projectors had the same 'white' level then the higher contrast ratio projector should have a darker black.  But not only are lumens and contrast not actually a measurement of the white and black levels, there are also multiple to ways to measure both.

The ANSI contrast test uses a black and white checkerboard pattern and is measured at multiple points on the screen.  This is a more strict test as it is measuring the actual contrast within an image.  However, some manufacturers rate their projectors at full on/full off, which normally results in larger contrast numbers.  Some manufacturers apparently even 'cheat', such as disabling the clear element of the color wheel on DLP projectors when measuring the 'full off' condition (it is not truly cheating since this can be done, however you can't actually obtain the contrast ratio that results in any real use).  So it can be difficult to directly compare contrast ratings.  Lumens output is usually a bit more standardized, but can also differ.  In addition, how the projector itself is setup and adjusted can have a significant bearing on the resulting black level.

The result is that you could potentially have a single projector with several different lumen and contrast ratings depending on who you adjusted it and how you measured the values.  So without knowing the actual black levels or that everything is equal, it is much more a theoretical than practical comparison.
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Brad Weber
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Ben Lawrence

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Re: Black screen on projection
« Reply #13 on: March 04, 2009, 12:19:44 pm »

For the record not sure if anyone cares but I ended up solving the problem by using a black desktop on my mac and there is a feature that shows your desktop without any folders so I ran that through the a/b switch with the dvd.
The room was light enough so the projected black was not noticeable. Thanks for the suggestions though all.

waldo [Casey Williams]

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Re: Black screen on projection
« Reply #14 on: March 05, 2009, 06:06:15 am »

Thanks for that. Sounds a lot like loudspeaker 'measurements'. I guess I'm not surprised.

best,

waldo
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Paul Lipp

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Re: Black screen on projection
« Reply #15 on: April 21, 2009, 01:59:23 pm »

My personal fix for this is, I use an analog way OctoLogo, for my switching between projector sources, and i have a few still in the frame memory, but you can also use solid black. I know this isn't the cheapest method, but if your looking at adding other features in, it could work for you.
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