Re: Do people prefer CIH setups? - Home Theater Forum and Systems - HomeTheaterShack.com

 
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post #1 of 6 Old 01-17-08, 12:59 AM Thread Starter
Mark Techer
 
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Re: Do people prefer CIH setups?

Hi guys.

This is my 2nd post here, so I would like to contribute my knowledge on CIH.

An Anamorphic lens magnifies an image in just one direction - typically horizontally. There are two main types of lens - cylindrical and prismatic.

The prismatic types can be found as either Horizontally Expanding (HE) or Vertically Compressing (VC). Cylindricals generally tend to be HE lenses.

Reading the previous posts and lens distortion seems to be a main concern.

The most common form of lens distortion is typically "pincushion" from Horizontal Expansion Anamorphic lenses where the centre of the image in both H and V plains is not as large as the ends. I say common because of the cost of the lens, all produce it to a degree - even the almighty ISCO III.

Pincushion can however be reduced by extending the throw ratio. The throw ratio is found by dividing the native 16:9 image width into the distance from the screen to the lens of the projector. If you aim for 2.0:1 or above, pincushion is generally a non-issue.

The other point to consider with anamaorphic lens is CA or Chromatic Abberation which is a bi-product of bending light. The more up-market lenses like the Panamorph UH380, ISCO III and Prismasonic's H1400/H1500 range all have corrective optical elements that cancel the CA by using glass types with different optical properties.

The entry level lenses generally do not offer this type of correction due to the cost. However, the amount of CA can be reduced by simply extending the TR as the beam angles are not as extreme as they need to be at short throws.

Zooming of the image is one sure way to avoid both pincusion and CA (unless the projector lens introduces one or both) but wastes precious veretical resolution. With HD it might seem that big a deal, but in the end of the day, your comparing 1080 pixels up against approx 810. Also when you zoom, your pixels increase in both the H and V direction, increasing the chances that you might actually see SDE. I have read coutless posts of 720 owners wanting to to move to 1080, then only to read that they now want to zoom for Scope.

In my honest opinion, using the full rez of the projector combined with an anamorphic lens is the only true way to project Scope...

Mark
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post #2 of 6 Old 08-09-08, 10:05 PM
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Re: Do people prefer CIH setups?

I have prismsonic v1000 which makes my setup constant width. However, anyway you can go scope the better.
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post #3 of 6 Old 08-10-08, 03:53 AM Thread Starter
Mark Techer
 
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Re: Do people prefer CIH setups?

But with a VC, you can still do CIH and scale either with the projector, or external scaler/HTPC. The only thing is when doing this is that you don't move the lens out of the light path. In the case of Prismasonic Lens, not using the pass mode...

Mark
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post #4 of 6 Old 08-10-08, 12:58 PM
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Re: Do people prefer CIH setups?

Exactly......i like the fact that all i have to do is adjust the lens instead of moving it. However, moving is not a problem with a diy lens slide.
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post #5 of 6 Old 08-10-08, 07:44 PM
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Re: Do people prefer CIH setups?

tbase..Looks like you have a nice theatre..
It would be good to see some full size pics posted in the Anamorphic Projection Theatres thread!

Prof..
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post #6 of 6 Old 08-10-08, 08:34 PM
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Re: Do people prefer CIH setups?

Thanks...as you well know.....we are never finished. My last project is to mount a 22" lcd flat screen for my bistro table. Setup my saltwater tank. Do a little decor. work and I think I'll be done. When I learn how to take good pictures I'll post some full size ones.
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