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Discussion Starter #1
Don't have much time to word this correctly.


Considering DLP technology, as with LCD is prettly much constant among the same generation models, in the sense of theri ability to obstruct light output in order to make a black image, would it not make sense than, that if you increase the lumen level, you increase the absolute black level?


For the Sanyos with 2000+lumen, and these DLP's with 1200 lumens...are these not going to have higher absolute black levels than their lower lumen counterparts?


I am NOT TALKING ABOUT CONTRAST HERE. I am talking about absolute black level.


I am almost certain that with a complete black 0 IRE signals, these things would surely light up the screen to a nice, bright grey. I can't see how it wouldnt.


Some more time:

My point being this...I assume that both LCD and DLP, using the same panels in different projectors, have some type of capacity of light they can absorb.reflect before it gets onto the screen. LCD, for instance, can only get opaque to a certain degree, at which point, any increase in illumination would increase base black level. Correct? I don't know how DLP works in this regards, so I can't comment.


I have no idea about D-ILA either, so I can't comment about it.
 

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Quote:
I am NOT TALKING ABOUT CONTRAST HERE. I am talking about absolute black level.
Actually, contrast ratio is exactly what you are talking about :). Each generation of LCD and DLP engines offers a particular ballpark of contrast ratio. So projectors within the same generation that have brighter lamps must necessarily have an increased black level.


Dave
 

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Discussion Starter #4
I see, in that you have interpreted it like this:


Contrast ratio = lightest/darkest.


So,


If contrast ratio is equal among various projectors, then increasing brightness must invariably increase absolute black level to maintain the claimed contrast ratio... correct?
 

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Yes if you have no control over the screen. One can always bias the black level to any desired level by using a darker screen. The extreme is black felt.


That's where contrast ratio and brightness come in. The best thing about a bright projector is that the brightness increases the dynamic range in ambient light. Contrast sets the absolute contrast ratio. For a given brightness and contrast ratio, there is a maximum tolerable ambient level that can support the contrats level.
 

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The absolute black level is the rated lumens/contrast ratio.


A 2000 lumens projector with a 1000/1 contrast ratio will have a black level of 2 lumens.


A 1200 lumen projector with 400 to 1 contrast ration will have a black level of 3 lumens.


This assumes the lumens and the contrast ratio specs for the projector are correct. Truth may be hard to find.


If you want to have a certain black level, then you attenuate the output light level with a device like the one shown at

http://www.edmundscientific.com/Prod...productid=2050


I don't know if anyone makes a variable light attenuator for projectors.


If you just want the blacks to look black, you use a bias light that you see but does not shine on the screen. You can then adjust the light so that the iris in your eye will adjust light levels to make the lowest light level look black.
 

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Discussion Starter #8
I like the math there, makes it easy to understand!


So, we need a 1500 lumen projector with a 5000:1 contrast ratio...hmm...
 

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No, you need a 5000 lumen projector with >1000:1 contrast ratio and a 18% grey screen with 2.0 reflective gain. (net gain of .36)
 

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Discussion Starter #10
Just keeping this going....is there any definitive answer for this?


In a given projector, if you increase lumen, do you increase absolute black level?
 

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Does that mean that my W400 (400lumens but like 270 in real life) has better ABL than a Sony 10HT? Thats kind of odd since most people think that it out does the 400 in black level. Maybe is the perceived black level thnks to the higher contrast...any ideas?
 

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Discussion Starter #13
You didn't read carefully :)


I said for a given projector..not all projectors. For instance....the sanyo 18, and 21, are identical except for lumen level.


The 10HT panels are most likely more advanced than the 400q...and the newer generation panels keep getting better.


But, within the same generation of projectors...I guess we agree then that increaseing lumen increases black level.
 

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Quote:
Originally posted by Erik Garci
Let's say there are two projectors that are identical in every way except lumens, and both of them are projecting onto identical screens.


Result: the one with higher lumens has a brighter black level.
Yes, but in a dark room you can make the lowest light level look black with a bias light. In a not so dark room you can't correct for a low output level except with a higher gain screen.
 

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I wonder why nobody tries to work with a normal and cheap lens aperture.


They use grey filters but why not use a lens aperture in front of the pj's lens? Then you can adjust the black level according to changing light situations. Use full 1000 or 1500 lumens for watching sports in a not too dark room and reduce the ouput to 200 lumens in a totally dark one.


I started doing this (I still have to find a nice lens aperture, so I am in an experimental phase) and the results seem to be quite good.
 

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Quote:
Originally posted by David Mendicino
What does that do to your white level?
The contrast ratio will remain the same so cutting the dark level in half will also cut the white level in half
 

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Quote:
Originally posted by joswig
I wonder why nobody tries to work with a normal and cheap lens aperture.


They use grey filters but why not use a lens aperture in front of the pj's lens? Then you can adjust the black level according to changing light situations. Use full 1000 or 1500 lumens for watching sports in a not too dark room and reduce the ouput to 200 lumens in a totally dark one.


I started doing this (I still have to find a nice lens aperture, so I am in an experimental phase) and the results seem to be quite good.
I have always worried that this approach might do something to the optical quality of the image with the aperture after the lens, but maybe not.


I will be very interested in your results. It could be an excellent, low cost solution for people to optimize their light levels. I assume the best system would then be a bright projector with a high gain screen to give the maximum flexibility in light adjustment for different viewing conditions.
 

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If you put the aperture very near to the lens there should be not problem with image-quality.


The effect is, that the need to do focusing decreases when the aperture is more and more closed as every photographer knows.


In German this is called "Schärfentiefe", a word that can be translated as: Sharpness-depth. When you want to take a picture and want the fore and the background to be sharp, you need plenty of it ;)
 
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