If you are interested in modding your Infocus Screenplay 4800 vist this site:
theMax
This is in italian but there are many pictures so you can understand modding.
Hi.
Max

[Gary Lightfoot]

It's a good idea to add an iris like that, especialy if the projector is quite bright to start with.

I was interested in the contrast measurements, and noticed that whilst one said 1800:1 from 180 lux for white and 0.1 lux for black, the next reading said 80 lux and 0 lux, thus an immeasurable contrast ratio. That's just bad measuring. The meter should be closer to the projector so that 'black' is within the range of the measuring device and accurate measurements can be recorded. If the second measurement is suspect it makes you question the first (though it doesn't appear unreasonable).

Gary.

Hi, Gary.
In measurements the luxmeter was near the screen, that I considered the right position (do you think it wasn't?). Probably the problem was in luxmeter accuracy, because it was only 0,1: it would be better to have one at 0,001.
In my opinion more important are measurements in films screeshots, that give us a real contrast ratio.
Max

[Gary Lightfoot]

Hi Max,

You may want to try the following as you have a light meter:

For accurate lumens you can measure at the screen (place meter head flat against the screen facing the projector) using a full white image and then convert the lux reading to lumens by multiplying the lux by the area of the screen in square meters. For a 7ft wide 16:9 screen that would be 2.561sqr mtrs. If the lux reading was 180, then the lumens would be 460. You are getting 205 lumens with the modification in place.

To calculate your reflected luminance in ft lamberts, divide the lumens by the area of the screen in square feet - for a 7ft wide screen that would be 27.5625 so for a screen with a gain of unity, you will get 17ft lamberts (205 divided by 27.5625). If the scren has any gain such as 1.2, then multiply by that number. 17 is just above the recomended cinema levels of 12 to 16 and is OK as the level will reduce as the lamp dims with age. With the mod in place you are getting 7.4ft lamberts (a smaller screen will be brighter). 7ft lamberts may seem low, but is not unlike a CRT and is very watchable if you are achieving almost 2000:1 CR (IMHO). I would still find that image very watchable.

For accurate contrast ratio measurement, put the light meter on a tripod or something similar, and place the meter close to the projector so that it will get a good reading that is not close to the extreme end of the meters range - something like 2 to 3 feet away. It's better to have the meter able to read well above 0.000 when 'projecting black' so will get a more accurate reading. Being able to change the range of the meter without moving the metering head means you will get more accurate results as well (such as changing from measuring white to measuring black).

EDIT: I've just had another look on your website and I see you've done some ANSI readings too. Maybe you could try them again with your meter close to to projector for more accurate results.

I'd be interested in the readings you will get if you have the chance to take them again so that we can see what the real contrast ratio is with the modification in place. If you could take the measurements without the mod, that would be a usefull benchmark as a comparison to see how effective the mod has been.

Gary.

[cyberheater]

I'm surprised that there isn't more comments on this.

It all looks very promising.

What's the difference between fitting an iris or simply using a ND filter?

[Gary Lightfoot]

I think the iris reduces light output by funneling it tighter, which reduces the overall brightness, but also reduces light contamination through the lens so blacks become less effected by scattered light and help increase the CR (by a better black level) compared to the same pj without the iris. Can someone confirm that?

An ND filter reduces the light more or less evenly from black to white so the image is dimmed evenly leaving the CR unnafected.

Gary.

Hi, boys
I think is very different to use an iris or to use an ND filter.
Infact the iris changes the geometry of light, erasing the exceeding part. Colour doesn't change in tonality and becames more rich. Shadows in dark scenes improove clearly.
If you use an ND filter all the light is reduced, there isn't contrast improoving and colour are less rich. No changes were in shadows. Many people that before used an ND filter after trying iris on 4800 were very satisfied.
After my experience i can confirm Gary's hypothesis.
Naturally the idea applies to all pj.
Max

[Gary Lightfoot]

Like Cyberheater I'm surprised there isn't more interest in this mod. It looks relatively straight forward and the benefits are obvious. I'm surprised more modern projectors don't utilise it, especialy as those that do achive much higher CR.

Gary.

[cyberheater]

So this would be a good mod for my DLP projector.

Some questions for you.

* Where exactly does the iris sit in terms of the light path.

* How do you determine the dimensions of the iris and it's distance from the bulb.

* What does the iris need to be made from to withstand the temperature.

* Does it need to be painted black.

* From a viewing point of view. Is the image improvement dramatic.

* Is a variable iris possible.


What other considerations are there.

Sorry for all the questions but you've really got my interest here and i'm considering doing the mod to my BenQ PB6100

[Gary Lightfoot]

I can't give exact answers for placement etc, but I'm sure Max can.

I would definitely make it temperature resistant and black (painted metal perhaps), as you want to stop as much light bouncing around as possible. Size of the hole may have to be determined by experimentation, so you can decide how much brightness you can live with.

You might be able to make a variable iris by having a moving part come out of the top of the case so that you can move it up and down. It'll have to be able to stop where you leave it as well.

The image brightness was visibly reduced on my HT1000 when I closed the iris, but I didn't measure the differences between open and closed. I might do that later though.

I'm sure Max will be able to fill you in on the details and even help you make it. Google might turn up some interesting info as well.

Gary.

[cyberheater]

Thanks Gary.

I've got you open my case soon to remove some dust blobs and i'll have a good poke around while i'm there.

hi
The iris sits before the lens, in the center of it (you can also link the iris to the objective, if you prefer); in theory the size of the hole depends on the installation: ambient light, distance between screen ad pj, pj ANSI lumen and naturally personal taste. The important is that every pixel is visible in the screen.
I made the iris in copper and after I blacked it with an heatproof paint.
I think that the image improovement is clear, dramatic in some aspects, as black levels and shadow details. If you are able to understand italian in the site there is a link to a tread about the iris.
I have a project for a variable iris, but it is unfinished because I'm very satisfied with this size.
Max