Does 2.35 require curved screen

Pincushioning is so minimal at longer throws (1.7 and higher) that is easily eliminated with 2" screen masking. Definitely not needed.

With short throws (also requires ISCOIII or Panamorph UH380 lens) it certainly becomes more of an issue to maintain geometery in scenes. That's when I'd consider a curved or torus screen.

That is what a 4 meter wide (13.13') Torus should look like on an install that should be ready in 10 months.

Can you help me out? How do I calculate my throw ratio? I'm looking at 14' throw distance to a 105" 2:35:1 screen...add an anamorphic lens and I suspect a throw distance of 13 1/2' from the screen.

Thanks,

What anamorphic lens are you looking at?

With Horizontal Expansion type lenses (HE) throw ratio is calculated as {throw distance / unstretched 16:9 screen width}. If you're using an HE lens your throw would be ~2.3 (14/6). This assumes your throw distance of 14ft is fixed and you're projector can throw a 6ft wide 16:9 image from 14ft.

If you were planning on using a Vertical Compression (VC) lens you calculate as (throw distance / 2.35:1 screen width). If you're using a VC lens your throw would be ~1.75 (14/8). This assumes your throw distance of 14ft is fixed and you're projector can throw an 8ft wide 16:9 image from 14ft.

Ideally you want to use your projectors longest capable throw to minimize pincushioning and CA (chromatic aberration) which results in a different throw distance for an HE lens vs. a VC lens. For the same projector at it's minimum zoom (longest throw) using an HE lens will give a shorter throw distance than a VC lens. Thus depending on your room and ideal projector location choose the anamorphic lens accordingly.

Mike

Thanks Uatoka, that's helpful for someone like me just entering the CIH game.

I was originally considering an ISCO 3 anamorphic lens (which way does that stretch?)

However, with glowing reports of the new (and much cheaper than ISCO) Prismasonic H-FE1500R lens I'm leaning that way, in terms of financial sanity. The Prismasonic site states that lens does horizontal expansion. That means I should be ok (doesn't it?)

Thank you.

Check your pj information on the projector calculator on projector central or one of the many sites out there that have them. If you are unsure post your projector brand and model here and I'm sure someone will know more about it.

If money is no object and you are going with a 1080p pj you might want to stick with the Isco III from what I have read. However, I like the idea of the Primasonic not having to use a sled and not having to re-focus.

With the ISCO III, I never feel the need to move the lens. Once in a while I squeeze the material to 1:85 with the DVD player, sometimes I use the zoom on the cable box. Most of the time I either stretch letter box material or just leave other material alone. It all looks great. I hated spending the $, but enjoy every hour with the ISCO III.

They're both HE lenses so if you want to keep your current throw and screen height (just go wider) then you're all set.

I think you'll be happy with either lens, enjoy!

Mike

Until someone does an AB test between the Isco III and Prismasonic, I wouldn't assume the performance of the two are totally equal.

I believe the Prismasonic still uses a fixed astigmatism correction element, while the Isco III uses adjustable astigmatism correction.

Vern

I've been to Alan's and have seen his curved screen, it's very cinematic. He showed me a few different lenses, Isco 3 and Prismasonic with a corrective lens, both seem to perform equally to my eye. I like the Prismasonic because it's motorized.

~Yvonne

With a short 1.55 throw ratio using a Panamorph UH380 HE lens, would pincushioning be noticeable watching non test pattern programming on a 2.35 flat screen?

Thanks,
Tom

Cineramax,

Great looking proposed setup! It's interesting to me that your side walls and back wall are lighter in color than the ceiling. Are those really the colors you plan on using, and if so, is there picture quality advantage to it?

I have the Isco 3 lens and the greatest thing about it is like its like having no lens at all, you really cant tell that you moved another piece of glass in front of your lens, Alan swears by it and he has all the lenses, the flexibility alone and the fact that it can be used over and over again with just about any projector in different circumstances is worth it, anyone who thinks that once they buy a lens specific for their p,j throw distance and setup that they are all set is just fooling themselves, pjs get changed out more times than we care to admit and with the falling prices of projectors that will only increase so if one can stretch it the Isco is the way to go, far too many times I see projectors for sale and the lens t hat they used right behind it in the classifieds.

The only time I notice it in material is with geometric structures (pillars, walls, etc). I am the only one that notices it however. Guests never pick up on it...I have a throw of 1.9.

With 1.55 it will be more pronounced, but how much you'll notice it is up the person.

Agreed Vern. I think in this case it's more an issue of budget, not performance. I think most would opt for the ISCOIII, but at 2-2.5x the cost of the Prismasonic the ISCO is out of reach for many...

Thanks for your input. I made a mistake in my calculation. For a 45" high screen my throw would be 1.68 and 1.78 for a 40.5" high screen. I wonder if I would be better off going with the smaller 40.5x96 screen and just use the zoom method with my Sony Pearl 1080p projector in my small 11'x13' room. I only have a max lens to screen distance of 1135". I would hate to spend thousands on a lens and scaler and have problems with the picture due to my short throw.

Tom

Did you mean you have a max distance of 135"? The reason I ask is that I figured for a 45" high screen you would have a 16x9 image of 80x45. So you take 135/80 and you get about 1.6875 which is what you said. If you did a 40.5" high screen you would have a 16x9 image of 72x40.5. Now you have 135/72 which give you a TR of 1.875. I think 1.875 should work. That's ths size I was thinking about. Granted, I expect to have a TR of over 2.0.

Cineramax,

nice layout. i'm a fan of the Dynaudio Temptations.

i know you have considerable design experience; but i wonder if the sonic effects of a curved screen are figured into your design?

what prevents the sound reflecting back to the listener and the curve focused reflections destroying the beautiful Dynaudio direct sound?

have you actually built a similar type theatre and listened?

i'm very curious.

Yes I have Mike. It was a 11 foot wide 1.66 aspect Ratio Flanked by the McIntosh 7 foot high(1993) that had 4x 12" and like 24x 1" tweeters. By positioning the loudspeakers forward of the screen and having heavy drapes behind the speakers and seating area very little sound goes into the screen.
The room was Rococo design (not my cup of tea) but the dede concept worked great. That was a prologic system whwere much of the soundfield was coming out of the left and rights. One of the best sounding McIntosh rooms ever. 2 ikw monoblocks.

Notice the selection of Dynaudio's D'appolito type controlled directivity keeps the sound from creeping into the screen as well, like a B&W 800 would inevitably do.

There is a huge difference in the parabola with the 1.66 short radius and the 2.35 long radius, so this combination of factors assures the desired results. The image is horter vertically cutting doen on the volume of reflected sound, and also the radius is very moderate, it is focussing on a point 1.5 to 2 times bhid the rear wall.


These are the techniques being used to eliminate the echoes this time around:


1)Absorption on the corner fronts,
2) large Controlled directivity speakers
3) Maintaining the image height short vertically
4) Accomodating the screen optimum light ray trace to the anamorphic lens pincushion and focus (that is a compromise that is determioned by the expert in the screen factory). The result is a SHALLOWER CURVE/Longer Radius.
5)Absorption on the rear centre wall to eliminate the bounce forward.
6) Not pointing any side or surround speaker or speaker lobe towards the front where the screen is. Create killing zones with the surrounds from top down -with directivity control as well, or from the sides in) Be careful not to mount speaker with passive radiators or powered speakers in the ceiling they will not work the radiator wont move , the amp may heat up.If you use a dipolar side surround you will hear it coming from inside the screen, so avoid.
7) Mount the screen in the upper 1/3 of the wall which creates a faint point of focus 18" above any listeners heads thus imperceptible.

I am very confident that it will sound fantastic. Better than the last time.

thanks for the answer. so with some fairly involved counter-measures it can work.

Indeed I expanded the list and posted a pic.
Regards

Thanks Ml Brand.

Yes the Torus screen will be the best possible CIH screen when you are going 11 feet or wider, you could make one 21 feet by 9 feet, there is no size limitation.

As great as the perf screens are some people have objections at the slight dot artifacts and the loosing of some pixel chunks. Also because the screen directs light into the audience only (making it an Optical screen by definition) it eliminates kick back light, that and having near perfect white fireld uniformity GIVE IT the higher MTF and virtual reality looking depth, because in reality we have perfect uniformity.


Re colors selection:
No the colors are used to make the picture more palatable ( i did tried a few colors, those worked best), in reality that front field of vision will be as black as possible. With suede paint in the ceiling and speaker cloth and black velvet sides.

I made a mockup of the screen box, the circle in the middle is where the proximity sensor will be sunk in to reduce the screen depth by 3.5".

Then I paint over where the walls would be, cut an paste the screen and speakers.

The 4 meter wide screen is just optimal for that room 3" inches shorter heightwise and the screen becomes too small.

Hi Tom,

I think you'll be fine with either...although I agree with Mustang. With a 40.5" height you're looking at 1.875 throw which is going to be better with regards to pincushing.

That's essentially my throw and where I really stop seeing it in video altogether. I only rarely noticed it at a throw of ~1.7.

The zoom method is a hassle to constantly adjust (zoom, lens shift, focus, etc), you lose resolution, and precious lumens. I think the lens option is personally the way to go. The benefit is cost and short throw negatives with an anamorphic lens.

Cheers,
Mike

This is the overall direction, but in reality it will look less like a "Whore House"- a concern my client expressed.

The side cabinets will store media and will be wood and slate and have diffusion and grids etc etc.

It is a lot of work. just finding out the right speaker for the ceiling is a pain.

Probably something from the Dynaudio acoustics line:
http://www.dynaudioacoustics.com/Default.asp?Id=290

How do I calculate throw ratio for a 2:35:1 screen? Do I take the width of my 2:35:1 screen (in my case, 105" wide) divided by throw distance (in my case, 162")?

Or do I work off the width of what a 16:9 image would be from my throw distance?

Thanks.

It is: distance from projector lens to screen divided by the width of the native projector image (16:9).

Great, thanks usualsuspects. That would put my throw ratio at around 2.025 (if I've calculated right: 13.6' from a 80" wide 16:9 image). Which I gather is a decent throw ratio for a CIH set up.

2.0 or higher is a good ratio. My TR is 2.25 - I have a small amount of pincushion on my UH380 lens.

Thanks Mike I am a little hesitant to dish out $2,500+ for a lens and scaler for a tiny 40.5x96 screen. I currently have a 45x80 and it would be very difficult to go to a much smaller 40.5x72 16 by 9 screen image. The last thing I want to do is spend big bucks and have noticeable pin cuchioning. It makes me wonder if I go small at 40.5x96 that the loss in resolution would be noticeable but less so than pin cushioning as I only watch HD movies? In my all black velvet room I have more than enough light output to do the zoom method and don't mind zooming, shifting etc.. If I knew that 45x106 would not have noticeable pin cushioning I would go the lens route.