i need help choosing a ND filter please.

ND filter will not improve contrast, but lower light output. If your display is too bright or you prefer darker absolute black levels (along with dimmer whites), then an ND filter is appropriate. Better, though, is a lower-gain screen. This will improve CR if you have any ambient light in the room, and it can also improve ANSI CR.

I am using a Hoya ND2 filter with my InFocus 7210 and MUCH prefer the picture quality with the filter over the picture quality without the filter...and, to complete the picture, I am using a 92" diagonal Stewart FireHawk with the projector and seating approximately 14" from the screen.

enigma, suggest that you either look in the manual, call the dealer or call the manufacturer...for example, my InFocus 7210 is threaded to take a 72mm lens which fits like a glove.

Use a millimeter scaled ruler to measure the inside diameter of the lens housing. That will get you into the ballpark (if the information isn't in your owners manual). Measuring with a machinsts caliper is more accurate (but they are more expensive than a good 6" metal metric ruler from OSH, Home Depot, Lowes, etc.).

NOTE: A ND2 filter cuts your lumen output by a factor of 2 (a calibrated 800 lumen output will be cut to 400 lumens). An ND4 filter cuts it by 4 (usually way too much unless you have a real light cannon and a high gain screen). ChrisWiggles suggestion is the better choice. The use of an ND2 filter will give the impression of better blacks, but it does not (and can not) "increase" the contrast ratio.

Anybody know the thread size of the JVC RS1 lens?

Looking to add a Hoya ND2 1 f-stop neutral density filter for the first 800 hours
of lamp life on a Da-Lite HighPower, 2.35:1 setup.


Setup:
The RS1 projector will be mounted around +25 degrees vertical offset (about 4.5 degrees angle above screen centerline) and the optimum seating position places the viewers eyes about 5 degrees angle below centerline.

This places the best seat within 9.5 degree cone, which will yield a gain of at least 2 up to 2.2.

The screen is 52" by 122" 2.35:1 (area of 44 square feet) squeezed by VC anamorphic lens and with a 20' 5" throw, equates to a TR of 2, near the middle of the zoom range but closer to the brighter but lower contrast end of the lens' zoom range.

With a new lamp on normal setting, calibrated to D6500, the reported lumens is around 562 L

562/44= 12.7 f.l. times 2.2 gives around 28 f.l. and 14 f.l. when the lamp drops to 50% brightness

I know some may reason that brightness level would be fine but I am aiming for movie theater, not TV brightness levels.

Trying to equalize the perceived brightness over the lamp life by cutting down the first 400 to 800 hours out of 2000.

Thanks in advance!

Inside diameter is 78mm. People have been using 77mm filters with no problems. Some have even taken the RS1's lens cap, cut out the center and used a 67mm filter:

Just what I needed.

Thank you kindly, SmithFarmer!