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post #1 of 12 Old 03-16-2020, 09:22 AM - Thread Starter
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Conversion lens calculator? Advice?

Yo. I have a JVC RS 4910. If I put one of the Navitar Mini Screenstar .65X lenses in front of it (which I think will work?), what is the best way to do the math for that?

It gives a 50% increase... have I read that correctly?

So if I'm looking to project a 110" x 62" image from the closest possible distance... and the Projector Calculator tells me that is 12' 10"...

And here is where I get confused. Do I just multiply 12' 10" by .65? Or by 50%? Or?

Or is there a limitation based on the size of the Mini lens that prevents me from placing the projector as close as possible?

Thanks.
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post #2 of 12 Old 03-16-2020, 07:30 PM
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You would multiply by the throw ratio. The minimum throw ratio of the projector is 1.4, so you would multiply 1.4 x 0.65 for 0.91. Though Ive read with these lenses you can induce vignetting at or below a 1.0 throw ratio. So instead say you went with a 1.1 throw ratio and a 110" wide image you would place the projector with the lens 121" from the screen.

Note the lens will also reduce lens shift by that 0.65 as well.
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post #3 of 12 Old 03-16-2020, 08:22 PM - Thread Starter
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Duh. That makes too much sense.

Next stupid question... has anybody ever put one of these things in front of an A lens?
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post #4 of 12 Old 03-16-2020, 08:45 PM - Thread Starter
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Or would you want to put the A lens in front of it?
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post #5 of 12 Old 03-16-2020, 09:03 PM
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For the HDSSW065+JVC (with using 0% lens shift with the Navitar about as close to the primary lens as possible) my measurement was that I was able to achieve a throw ratio of 1.02 without vignette and for 2.35 material a throw ratio down to 0.96 without vignette of the 2.35 portion of the image. If you use lens shift you need to align the lens to the image axis which causes the Navitar lens to be further from the primary lens which will further reduce your achievable effective throw ratio (sorry, I did not measure for this case).

The Navitar Mini lens will be woefully insufficient for your JVC.

You would not be able to then place an anamorphic lens in front of the conversion lens, even the huge ISCO 1.25x is too small for this; nor would it work the other way around.
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Last edited by jjcook; 03-16-2020 at 09:48 PM.
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post #6 of 12 Old 03-16-2020, 11:25 PM
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Quote:
Originally Posted by jjcook View Post
For the HDSSW065+
Are you aware of anyone using these lenses, the hdssw065/08, with 0.95 dmd projectors? Even better with the LED versions?
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post #7 of 12 Old 03-17-2020, 06:37 AM - Thread Starter
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Quote:
Originally Posted by jjcook View Post
The Navitar Mini lens will be woefully insufficient for your JVC.
Yeah? Hmmm. Because of the size, you mean?
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post #8 of 12 Old 03-17-2020, 01:34 PM
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Quote:
Originally Posted by bdht View Post
Are you aware of anyone using these lenses, the hdssw065/08, with 0.95 dmd projectors? Even better with the LED versions?
No, sorry, I'm not -- generally both the HD065/08 would be a good fit (again maybe not to the maximum expansion ratio like the JVC).

Quote:
Originally Posted by Dennis Moore View Post
Yeah? Hmmm. Because of the size, you mean?
Yes because of the size of the entry/exit lens.

I didn't look at your requirements but the SSW08 has a reasonable-sized lens that can work in many scenarios if you're not able to step up to the HD-sized lenses.
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post #9 of 12 Old 03-17-2020, 01:54 PM
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You should measure beam size.

At min throw ratio there is a vary large beam that does not fit anything but the super large lens.

Adjust your zoom to max brightness and put a piece of paper in front of the projector where the lens would go.

Mark the paper and measure how wide the image is the see if the beam would even fit the lens.
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post #10 of 12 Old 03-17-2020, 02:30 PM
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Quote:
Originally Posted by Dennis Moore View Post
Duh. That makes too much sense.

Next stupid question... has anybody ever put one of these things in front of an A lens?
Would not work. The image exiting the A-lens would be way to large for the Conversion lens.
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post #11 of 12 Old 03-17-2020, 02:32 PM
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Quote:
Originally Posted by Dennis Moore View Post
Or would you want to put the A lens in front of it?
Same problem. Exist image would be too large to fit into the other.
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post #12 of 12 Old 03-17-2020, 02:33 PM
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Quote:
Originally Posted by kemannthey View Post
You should measure beam size.

At min throw ratio there is a vary large beam that does not fit anything but the super large lens.

Adjust your zoom to max brightness and put a piece of paper in front of the projector where the lens would go.

Mark the paper and measure how wide the image is the see if the beam would even fit the lens.
He can save some time. I can already tell you you can't use a mini with the projector at short throw, wide angle.
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