How 'black' is the black on most projectors?

[gyro_gearloose]

I've got an idea for a lighting effect using projectors, but the success of my idea depends on the black part of the projected image being completely and utterly black. How well do most projectors project 'black'? I've seen quite a few projectors that project a kind of dark grey-ish box when the image is completely black. This is not acceptable for the effect I've got in mind (and sorry, but I don't want to give away too much about what I'm trying to acheive just yet, before anyone asks). Do all projectors do this, or do different types give different results - DLP vs. LCD, for example? I suppose I could always use a polarised filter in front of an LCD projector and turn the filter slightly such that the black truly is black, although this would obviously cost some light output overall.

[Shez]

I've heard it said that DLP is better than LCD in this respect but from my own experiences, neither technology produces a complete black. Even digital projection in the cinema doesn't quite manage it...

[jason5d]

dlp is better at projecting black.

We recently did an arts show/space at testbed1 in london

that was about shadows and video projected on paper so

black out was really important.

 

We used 2k casio led/dmd projectors for 8ft images of

pre-made video and static cameras around the space, to

great effect

[Brian]

dlp is better at projecting black.

 

 

[PEDANT]

Surely you mean..."dlp is better at not projecting white."

[/PEDANT]

 

I'll get my coat.

[CallumP93]

I've got an idea for a lighting effect using projectors, but the success of my idea depends on the black part of the projected image being completely and utterly black. How well do most projectors project 'black'? I've seen quite a few projectors that project a kind of dark grey-ish box when the image is completely black. This is not acceptable for the effect I've got in mind (and sorry, but I don't want to give away too much about what I'm trying to acheive just yet, before anyone asks). Do all projectors do this, or do different types give different results - DLP vs. LCD, for example? I suppose I could always use a polarised filter in front of an LCD projector and turn the filter slightly such that the black truly is black, although this would obviously cost some light output overall.

 

I have found with most projectors you can not get rid of the "black" square and it is still there on the more expensive projectors (well at least the ones I have worked with). I have seen people trying to use projectors as a kinda followspot, and there was a post on blueroom a while back about someone trying to get kickstarted funding to produce a app for this, but the gray square was obviously one of the downsides. What you need to look at is a projector with a high contrast ratio than your average 1:1000, which should then give a darker "black". As you suggested you could use a ND filter / gel to get rid of most of the gray. Another option is there the option to rear project as it doesnt normally show as much then? Th

[Jasonbrownstuff]

we use DMX shutters

you can put them front of the projector and the add the m to your cues on the lighting desk

we have the min hire stock if that helps

http://www.technicalsolutions.org.uk/hire/DMX-shutter

[alistermorton]

we use DMX shutters

you can put them front of the projector and the add the m to your cues on the lighting desk

we have the min hire stock if that helps

http://www.technical...ire/DMX-shutter

 

That's what we do when we want to completely black out the projector too.

[CallumP93]

I was going to suggest a DMX shutter but it seems the OP wants to use the projector to do something without the square not black it out.

[AHYoung]

contrast ratios arnt what they seem. R=The savey manufacturer will modulate the lamp power dependant on the source, so when you fade to black, you get a pretty good black, however if you want a gobo beam effect with a white line, the lamp power ramps up and the black ismore of a dark blue grey. generally dlp units due to the way they work have darker blacks than lcd or lcos based units, and the better the unit the better the results. Paper specs are pretty much a waste of time due to the way the ratios are measured, so its down to experimentation. Polarising filters, ND, shutters whatever wont help you as you are looking to reduce the black levels without effecting the white point, just making it all darker doesnt help as its the relative contrast you need to change.

 

Over the years ive experimented quite a lot with projectors as beam effects , in much the way you'd expect someone who owns a large number of data projectors AND a whole load of optikinetics units. Basically what ive found is that the lack of depth of focus, relatively large pixels and dissapointing actual black levels make it not as impressive an undetaking as youd like.

 

I have however had some success with the casio led units which are actually very underpowered , but they have fairly unique optics with a fairly narrow angle so when you combine them with the mirror units from a Golden scan 3, they become a interesting moving light...

 

 

High End, Robe , christie etc have all at points made/make a digital moving light and as far as im aware, none really do anything outstanding and have never really caught on as lighting fixtures and dont offer anything usefull as a traditional projector. so maybe the fact that the products have been available and never really caught on answers the question...

[Hugh]

Surely the laws of physics dictate this will never be completely successful, after all how can you turn a white screen (reflects all colours) black (absorbs all colours or absence of light) by shining a light at it!

 

But I am a noise boy so what do I know!

[Shez]

Surely the laws of physics dictate this will never be completely successful, after all how can you turn a white screen black by shining a light at it!

By not shining light at it. Which is kind of the whole point of the question ;)

[gyro_gearloose]

High End, Robe , christie etc have all at points made/make a digital moving light and as far as im aware, none really do anything outstanding and have never really caught on as lighting fixtures and dont offer anything usefull as a traditional projector. so maybe the fact that the products have been available and never really caught on answers the question...

... or maybe it is because those products are very, very expensive so not many people could really justify buying them instead of more conventional moving lights.

 

Since what I wanted to achieve doesn't seem to be possible with current off-the-shelf projector technology I see no harm in telling you a little bit about my plans. I have been looking at the capabilities of the Raspberry Pi, and I wanted to use it to create a device which would have a DMX or Artnet input and would basically turn a projector into a profile. It would use the graphics capabilities of the Raspberry Pi to display gobos, change colour, and even have shutters. Not bad for a £30 device, eh?

[mac.calder]

... or maybe it is because those products are very, very expensive so not many people could really justify buying them instead of more conventional moving lights.

 

Nope... Definitely not the reason. A large lighting company I know (which does most of the big name concert tours here in Aus) bought pallet loads of DL1's - They went out for 1 or 2 shows, then sat gathering dust. They skipped the DL2's, however bought a hand full of DML's and DL3's. Same problem. The biggest problem is they are trying to balance size, weight and brightness. Unfortunately, to even come close to competing with concert lighting, you need at least 10k projectors. They just don't cut it.

[themadhippy]

and would basically turn a projector into a profile.

Didnt prg or someone similar do this back in the late 90's,seem to recall it wasnt colour just black and white

[AHYoung]

bash on and if you go for a lo resolution but bright cheapo dlp unit like an optoma es551which has the required hdmi connector, you should be be able to build a digital light for about 300 quid all in. remomber that 2700 lumens or whatever sound a lot, but thats a white square frame, and due to the very limited range of zoom {+-10%} compared with a profile you will have to introduce a digital iris / zoom thats wastefull. What you are planning is perfectly doable, its just id question as to whether the results will be useable enough - but they wont be far off.

 

Its a great idea, and you not the first with it, but at least its cheaper now than when I built something dissapointing 15 years ago and it wasnt anywhere near an original idea then. At some point, the technology with led lightsources, dlp chips and optics will allow this to happen bright and cheap and at that point one of the big boys will have a Digiprofile or Source 5 or whatever. The developement has all been towards moving light / projectors which frankly dont really do much, but instead a simple manual light probably has more potential.