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Author
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Topic: My projected picture is too small
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Winbert Hutahaean
Film God
Posts: 5468
From: Nouméa, New Caledonia
Registered: Jun 2003
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posted August 09, 2007 04:48 AM
Hi all,
Perhaps you remember this post, where I was telling you about my future projection room.
It is now almost finished and yesterday, I turn on the projector at the maximum distance between the projector and the screen at 0 degree. It is about 4.5 m in distance. I was using Elmo ST-800 (a very standard one with the lens did come from the factory, was it 1.2?).
The result was so unsatisfying me, because the biggest picture can be projected was only half of the screen size. The screen size is about 3 m x 4m.
My aim is to get at least 3/4th of the screen size.
I knew for the opposite issue there is a lens that allow us to project the film far from the screen with a result of small picture size. (Do we call it "throw lens"?)
So can we get a lens, where with my projecting area I can get a bigger picture ?.
I knew there will be an issue of less bright light output, but I will be installing ST1200 (150w, 15v bulb) for my permanent projectors.
thanks,
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Winbert
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David Pannell
Phenomenal Film Handler
Posts: 1072
From: Horsham, West Sussex, UK
Registered: Nov 2004
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posted August 09, 2007 06:59 AM
Hi Winbert,
I don't know what would be the best lens for you, but please don't fall into the same trap as some enthusiasts. You have to remember 'The Inverse Square Law', which means that the light varies inversely as the square of the area. Therefore, for a picture twice as wide, the image will be a quarter of the brightness - YES! A QUARTER!
Also, definition will be subject to the same law of physics, so the image again will be four times as grainy. As your projection distance is only 4.5 metres, or roughly 13 feet, I would be inclined to stay with the smaller image and use a screen to suit. But that's only my own humble opinion.
I have a fairly long lounge where I project, and from lens to screen is about 20 feet. I still only use a 1.5 metre screen, and sometimes even a 1 metre screen. I have tried larger, and I find visitors complaining that it's like sitting too near at a commercial cinema, and they either get headaches or feel dizzy.
Just one person's experience.
Best regards,
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Dave.
Valves and celluloid - a great combination!
Early technology rules OK!
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Jean-Marc Toussaint
Film God
Posts: 2392
From: France
Registered: Oct 2004
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posted August 09, 2007 07:37 AM
Winbert, in addition to what David just said:
The standard lens usually delivered with Elmos is the 1.3 / 15-25 mm. The biggest projected picture you will get at 5 meters, in 15mmm setting, will be roughly 1.3 x 1.8 m.
The 1.2 which is the fast longthrow lens (as opposed to the 1.4) is a 25-50 mm optic which will give you a 0.8 x 1.05 m picture at the same distance.
The shortest Elmo lens is the excellent 1.0 (scarce and pricey), which is a 12.5-30 mm, it will give you a 1.6 x 2.1 m pict (approx.).
If you want to go slightly larger, you need to find the Shneider Kreuznach Xenovaron lens, (also scarce but more affordable), it's an f:1.1 / 11-30 mm. You will need an adapter sleeve from CHC. But you wont fill your entire screen. 1.8 x 2.4 m should be your approx. image size then.
But you will soon notice that the larger the image, the darker it will feel, especially with a 150w lamps (even with an Osram Xenophot).
Adapting a two-blade shutter is an option but switching to an Elmo GS1200 or even a Xenon machine is right around the corner, my friend.
Welcome to your new nightmare... ![[Big Grin]](biggrin.gif)
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The Grindcave Cinema Website
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