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Yes, a static DIY iris is not too hard and actually improves ansi contrast figures.

However, a DIY dynamic iris is more doubtful unless you have electrical engineering experience, as it will require a method to measure and process on screen averaged output to correctly change the iris's setting, even more so the dynamic gamma needed to keep the gamma curve the same.

For a static iris you simply just need to place it just before the main lens assembly. It improves the ansi contrast as it prevents more scattered light from entering the main lens assembly and being focused with the rest of the projected image.
 

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Quote:
Originally Posted by jarrod1937 /forum/post/16971541


Yes, a static DIY iris is not too hard and actually improves ansi contrast figures.

However, a DIY dynamic iris is more doubtful unless you have electrical engineering experience, as it will require a method to measure and process on screen averaged output to correctly change the iris's setting, even more so the dynamic gamma needed to keep the gamma curve the same.

For a static iris you simply just need to place it just before the main lens assembly. It improves the ansi contrast as it prevents more scattered light from entering the main lens assembly and being focused with the rest of the projected image.

Yeah, i quite agree with you!
 

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Funny thing, I'm also owner of the HC1500 and I'm also thought about iris...
Manually setting of course...


But mine Mitz has more than 2 years to void of warranty, so then no tweaking or modding...



Floridapoolboy has right, I will probably go that way...



P.S. If you also exchange colour wheel (on 6 seg. RGBRGB) and firmware, then you will have... Mitsubishi HC-1100!!!
Which has little better blacks and contrast, but with less brightness...
 

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Yes, I was talking about a static iris. Are there directions anywhere on how to make one? What do I make it out of, how do you determine what size to make it, where/how should I mount it, etc?
 

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Quote:
Originally Posted by floridapoolboy /forum/post/16971537


Maybe, but it would probably be more trouble than worth. Get a high contrast grey screen instead!

A high contrast gray screen improves ansi contrast in rooms with white walls and improves the blacks, but darkens the whole picture equally (not that it doesn't look good). Adding an iris will darken the blacks more than the white, thus increasing the contrast ratio.


It increases the contrast partially because when the DMD mirrors reflect the white light away from the lens to achieve "black" (basically white at a much lower intensity) some of the light still makes its way back through the lens, because once the light is reflected away from the lens to the matte black area of the DMD/light chamber some of it is still reflected towards the lens, washing out the blacks more. When an iris is added it blocks even more of that light from bouncing back into the lens. It's a big difference in contrast and black level improvement.....without darkening the whole picture equally, thus retaining more brightness AND a higher on/off + higher ansi/contrast than using a gray screen.


BTW, to the OP, what I heard increases the contrast ratio the most is to make your iris in a vertical shaped Cat's. You can make it a circle, but if you make into almost a vertical oval it may increase contrast more. The more close, the higher the contrast, but the more close the more brightness will be lost (but the darker the blacks). You want it to be towards the center of the back part of the lens.


For mine that I made for my Infocus 4805 I used a cardboard paper and drew the brown part black with a pen. It seemed to work fine. Another way I did it was putting black electrical tape over it. It pretty much got cooked to the cardboard paper (the glue dried out), but seemed fine also. BTW, I taped it onto the back using electrical tape, too.


All in all...it's very easy & you'll love the better contrast/black level performance. It was a nice step up for my Infocus 4805, back when I had it. Now I have a DT-500. Actually, if I were you I'd just sell your unit and look into getting a Sharp DT-510 somewhere. You can turn the iris on and off, which is much better than having one you can't change with a push of a button. The Benq 8720, which is said to be one of the greatest 720p units ever can be had pretty cheap too.
 

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By using the homemade iris you're increasing black level at the expense of brightness. If you have a small screen that may be fine, but with a larger screen or dealing with ambient light you'll want all the brightness you can get. What the heck, make a quickie iris and try it, but I'd be saving for a better performing PJ and painting the walls and ceiling black if I were looking for better contrast.
 

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I did a iris mod to a Benq 6100 (back in 2003). Contrast and black level were very much improved. It did reduce the overall brightness of the projector but the trade off was worth it.


Some piccies here. Notice the cats eye / diamond shape. I read somewhere at the time that it was the best shape. I used black duct tape for the mod.



 

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I also modified my projector with a diy internal iris.

My projector is a Mitsubishi XD460U 2600Lumen, 2500:1 max contrast using brilliant color - white segment and not calibrated to d65 (being a business presentation projector the color wheel is not optomized for video) Darkchip3, XGA resolution. Screen is 7ft width, white painted wall Dulux Light & Space absolute white rich matt with Lumitec technology. Viewing distance is just about 8ft, room is a batcave.


The internal iris was 17mm diameter (227sq mm). I reduced it to 10mm diameter (79sq mm). It reduced light output but not as much as an ND4 filter, and still plenty bright enough for my 7ft wide screen in a batcave. The increase in contrast ratio was very noticeable, obvious in general viewing. The originally projector lens was F2.4-2.6. Texas Instruments recommend F2.8 or larger F number (smaller iris) and quote 2,300+:1 for the darkchip3. According to Projector Design Action model one mk2 to mk3 iris improvement going from F2.8 to F4 gives a 70% increase in contrast. I have measured it at >4,167:1 (not using brilliant color - white segment) at the screen using a digital camera and calculator.


If you are looking for more image depth. I would strongly recommend using gamma 2.5 if you are not already doing so. Also getting greyscale neutral d65. These two things along with the iris mod made the biggest improvements to my picture quality and all were very noticeable improvements.
 

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Quote:
Originally Posted by xlr231 /forum/post/16971419


I have an HC1500 and was hoping to get better black level performance from it. Is it possible to add an iris to it for darker blacks?

As others have said, an iris can be added. For the lens or just before the lens you could get something that I think is called Blackwrap, which is like aluminum foil with black over it. This is stuff that is used in stage lighting.


Where an iris should go can depend on the design, but if you can get the lens open there may be a place about halfway down the chamber that is good. At least with projectors like the Optoma H79 where there is already some kind of lens iris there at a spot that is reasonable for shutting it down further.


The real magic with DLPs is to combine a lens iris like that with an iris in the projector path after the light pipe and before the DMD. Placement here could be pretty critical as the shape of that iris can determine the shape of the most intense locations of the light going through the lens. With my H79 I closed down this internal iris location, then took the front of the lens off back to the iris and used a white piece of paper on a stick that I could put back into the lens of the plane of the iris with the projector getting something like a full screen 20% video level pattern. I could then see the shape of the most intense light coming through the lens and put an iris there around that so that most of the white got through, but black was blocked very well (since absolute black images create a more random light across the whole lens). If the lens iris was put in the wrong spot it could have hurt the lumens and the on/off CR.


I actually ended up doing a 4 iris kind of thing, but I don't necessarily recommend it. For the internal iris location I had 2 openings where one was clear and one was red. Then in the lens I had 2 opening that matched up with those with the same colors. The extra red helped balance the light from the bulb not being red enough and red is hard for us to see in dark images, so on/off CR for red isn't as important as that for blue and green. I was able to get around 9k:1 on/off CR this way with about 100 lumens and then used it with a 92" wide Da-Lite High Power screen that gave me around 2.4 gain. That was a few years ago and I'm not sure what could be done with other models, like much newer ones, at reasonable lumens.


Also, for the internal iris I used sheet metal that I drilled out and filed down to get the holes the right shape. I didn't make the internal iris dark and I don't think it made much difference. The lens iris has more chance of having reflections come back out, so more reason to make that one dark. At there isn't as much light in the lens, so should be able to get away with less robust material that is dark and so adsorbs light. It can be really hot inside.


--Darin
 
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