Iris?

Jeff

Distinguished Member
The only real downside is loss of lumens (not as bright).
 

jacko5

Active Member
hi...

just wondering what is the iris that is on projectors... increasing contrast i take it... but what effect has it on the projector??? does it shorten bulb life or lower PQ???
The iris is either manual, where you close down the aperture to taste, or automatic, usually described as dynamic. The Iris closes down for dark scenes to give darker black levels and opens up for bright scenes. It is designed to improve picture quality and has no bearing on lamp life.
 

tryingtimes

Well-known Member
Re: Dynamic iris
There are three ways in which an iris can annoy or compromise PQ.
Brightness compression: In a mixed scene (a starfield is always given as an example), the bright stars will be dimmed slightly, in order to give you a lower black level.

Noise (audible): Some iris implementations are noisier than others - often it's a high pitched whine, which can irritate.

Brightness pumping: This is where the iris acts so slowly that you can see the image change brightness during the scene. Pretty annoying, but getting rarer - especially with the newest models.

It's a trade-off, but with a good implementation (like the Sony VW60 for example), most are happy to live with it in order to get much more image depth in dark scenes. I haven't really heard any complaints about the Mitsubishi models either. I can't think off the top of my head how others perform.
 

Peter Parker

Distinguished Member
With a dynamic iris there is also dynamic gamma - as the lumens are reduced as the iris closes, the video signal is boosted to increase the white level, giving the impression the bright parts are still as bright but the darker parts are darker. Depending on how well this is implemented, you may find that there is not enough contrast available for the gamma boost to work in, so some compression of image data occurs in the brighter parts of the image.

As TT said, the Sony's seem to have by far the best algorithm for their dynamic iris.

Has anyone seen TIs Dynamic Black in operation on a pj? I would guess that would be pretty good too.

Gary
 
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Jeff

Distinguished Member
The only real downside is loss of lumens (not as bright).

I'm so used to using a manual iris I forgot about DI (dynamic iris), I don't like it, it makes the PQ yucky.
 

tryingtimes

Well-known Member
I'm so used to using a manual iris I forgot about DI (dynamic iris), I don't like it, it makes the PQ yucky.

Well yours was the first implementation :)
They might have improved since then. Although you never know - there are people who don't use it on the VW200 either.
 

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