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Old 04-19-2013, 08:46 AM - Thread Starter
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Sorry for reposting this....had put it on the general screen forum but had no responses.

As I would anyway be DIYing my screen figured it may have been better posted here in the first place:

We're renovating the basement and my home theater is changing rooms.

The new room is almost square and my main concern is it will be a relatively short throw for my projector.

Here's the beef:

Room dimensions: 370 cm in projector throw axis, 360 cm wide. Black projection wall, dark colours elsewhere, no ambient light other than screen.
Projector: JVC DLA-X35 (note this projector has a motorized lens with 5 user programmable lens memory settings for 5 combinations of a specific focus, zoom, and vertical/horizontal shift)
Throw distance: 312 cm (that is the maximum I can go - it leaves only 10 cm behind the projector to the back wall where the cold air intakes are and the manual specifies 20 cm)
Viewing distance: 308 cm
For what its worth, as we are renovating at this point nothing is built into this space so I can wire in, install, anything I want. Above dimensions are projected internal after drywall and include the standoff distance of the screen surface from the projection wall.

At maximum zoom for a throw of 312 cm the various calculators (JVC, projector central, elite) tell me I can get between 223-229 cm projected image width.

What I am thinking will be best here is a CIW set up and projecting a 220 cm wide image for all aspect ratios. I'll use a masking solution to close down or open up the screen along the vertical dimension.

My feeling is this will work best in my situation because:

This will give me the biggest projected image for all ARs without resorting to an anamorphic lens (2 m2 for 2.4 material and 2.7 m2 for 1.78)
I will certainly not have a problem with too little brightness even at close to maximum zoom - in this dark room if anything I may have to consider a screen gain lower than 1.0
The 5 programmable settings of zoom, focus, and vertical/horizontal shift should allow me to easily switch between 5 main AR projection requirements

It seems the majority of people here are fans of CIH setups but I think at least 3 factors specific to my case make a CIW setup more appropriate: the lens memory feature of my particular projector, the short throw, and my desire to have as big and immersive a picture as possible.

I'd appreciate comments to either reassure me it makes more sense for my situation or point out if there is something I am overlooking. For what its worth I don't give much credence to the view that a cinemascope picture should be "bigger" than 1.78 material. I only watch one film at a given sitting anyway, so the argument that there is an "oooh aaah" factor from seeing the masking panels on the sides pull outwards for 2.4 material doesn't sway me. I simply want to project cinema material in the aspect ratio it was filmed in and use all of my projector panels to their full capacity in a relatively short throw room.

Dave M

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Old 04-19-2013, 10:01 AM
DIY Grand Dad (w/help)
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Hi Dave...

Well, if you use only a Top "Horizontal" masking screen made from a Retractable Blind assembly, that would be easiest, by allowing you to simply shift the image down so the "Blind" just pulls down to the top edge of the image. Dual Horizontal masking would be / is quite difficult.

You are right...many are loathe to give up on a bigger 16:9 image, unless they have considerable "side to side" room to expand the 2.35:1 image enough to increase the 16:9 height along with such.

In any case, it's your own preferences that matter here.

However according to my figures, at 312 cm throw distance you cannot get anything bigger than 223 cm "wide" and that is only by maxing out your zoom...which is at least not wholly advisable. You need 10% left for formatting adjustments as well as maintaining optimal optical quality.

Even going down to 214 cm wide, I would suggest against considering a screen with less than 1.0 gain. The JVC employs an adjustable Iris along with it's superb Panels to get your Blacks into the cellar, but the lamp will age, and it's better to fully calibrate to a very light, 1.0 gain Gray, and run on low lamp. That givers you the best Blacks and longer Lamp life.

The DLA-X35 is a US Distributed unit so I'm supposing you brought it over with you or had it shipped in special.

Talking Screens.....can you paint onto the wall, or is a Substrate necessary? How high is the ceiling over the Screen? Your Screen size isn't huge, so it's height...if centered on the wall, shouldn't present too overly bad a reflection onto the Ceiling.

If your satisfied with watching primarily in almost absolute Light controlled darkness, and you have non-reflective room surfaces, then a very light neutral Gray tint mixed into Dulux "Light & Space" Matte White Interior Enamel (water based) should get you exactly where you want to be. Spray it on if at all possible, as you do not want the JVC's pristine, pixel-free image to be corrupted by texture or ("GAAAAA !!!"") roller marks.

"They said it couldn't be done. Well, we sure showed 'em otherwise!"
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Old 04-19-2013, 10:35 AM - Thread Starter
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Hey MM, thanks for responding. Man, I have learned a ton of stuff from you re screen construction now that I am looking to shift rooms down there. Thanks for that!

Now as to your points and questions:

  • Actually my model number is the DLA-X35BE which is the Euro distributed version that I bought here in Switzerland - land of chocolate, cheese and outrageous prices.
  • Re building: I have a blank canvas if you will....the room is currently concrete block so I will put up drywall and go from there. On reading a bucket full of threads per day last few weeks I am inclined to go with painting on a locally available substrate and not the drywall. In fact my question to nail down the CIW versus CIH is partially motivated by wanting to lock in my image size(s) so I can start searching around here for an appropriate substrate knowing what my size requirements are. I expect I should be able to find a properly Swiss mega flat and paintable surface although it may not be sintra or one of its aliases.
  • Re gain I also thought I would shoot for a paint formulation giving me something in the 1.0 - 1.2 range. FWIW I am running the projector in its current room now on the economy setting with the iris at -15 (lowest settting) onto a Dalite Hi-Power (from my old NEC LT-150 days) and it's great.
  • Re height to the ceiling - well the ceiling is a mess of pipes etc. now - I believe the technical term is a "way skookum" rats nest of pipes - so I will be putting in a dropped ceiling drywall installation with variable heights. Immediately above the screen, and projecting out of the screen wall the height off the floor will be 200cm for about 80 cm. After that it will be height of about 215 cm over the central corridor back to the viewing couch. Along either side the heights will dip down again to 190-200 cm for a 40 cm wing on the left side and a 1m wing on the right.
  • Re projected width....I think I am going to actually measure the projected width my projector will give me with good material at my maximum throw distance and ensure I am happy with the optical result at that level of zoom. That'll give me a pre-tried and tested maximal image width which is my main concern here. It depends on how they configured the optics - I do alot of photography and all zoom lenses are compromises but tend to work better toward their wide or telephoto ends. I will see what I can get out of this one but irrespective I'm going to build the screen wider and mask with side panels. I want to have a screen that I can pull out and replace or simply re purpose if I get a newer projector down the line.

My reading suggests a silverfire formulation seems to be the preferred potion but not so clear how Euro availability pans out on that.

Think that's all you asked about. Thanks for taking the time, and gotta say I love your avatar,


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