8mm Forum: Throw distance question.

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Posted by Michael O'Regan (Member # 938) on March 21, 2010, 05:48 PM:

With a 150w lamp and the Sankyo 1.4 lens, is a bright picture achievable from 22ft or is this too long a throw?

Posted by Steve Klare (Member # 12) on March 21, 2010, 06:10 PM:

Hey Michael,

I've thrown about that far with f1.3 and 100W and the picture was bright enough, I think more than anything it's how large a screen you are filling with that light.

If I remember right, when I get that for out, I'm zoomed all the way out to the 25mm end of my lens to fit the image on a 52 inch high screen, any further back I can't stop it from spilling off the screen edges.

One thing I did notice is sounds in the track that the projector's mechanical noise might normally mask become more bothersome with the machine far back and the speaker by the screen.

Posted by David Kilderry (Member # 549) on March 22, 2010, 01:14 AM:

Michael, it is the size of the screen, not the throw that determines picture brightness as Steve says.

eg a 3ft wide picture will be the same brightness if the projector is 10 feet from the screen or 20 feet from the screen.

David

Posted by Michael O'Regan (Member # 938) on March 22, 2010, 03:20 AM:

Thanks fellas - I realise that point about the size of the screen, but there does come a point at which a lamp is just not bright enough.

Posted by Steve Klare (Member # 12) on March 22, 2010, 08:17 AM:

I think what you are getting at is the ability of the air to transmit light over a long distance without distorting or dimming the image. This is the same problem that puts telescopes on mountain tops and even up in space. Down here on Earth, sometimes you look at the projector beam and you see all sorts of dust particles drifting through the beam and these are absorbing and scattering light, but it's not a big fraction of it. I would think if you have a room full of people smoking it's worse, but then again I think that by the time it's bad enough to really hurt the quality of the image, it may be a little too thick to breathe!

The lenses I'm talking about are also the standard ones the machines are delivered with. With ones like the Elmo long throw (25-50mm) lens, it should be possible to back up much further and keep the image on a reasonable sized screen.

We did some renovations on our house last year that added the area formerly a back porch to the usable living space of the first floor. This lengthened my longest possible throw from about 18 feet to something close to 30. Most of the time I don’t project any further than I used to because I find If I'm watching by myself in the living room it gets to be quite a commute every time I want to adjust the focus or volume or do a changeover.

I might do it if I was projecting films for other people and hanging around back by the machines anyway.

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