The dreaded long throw question - diyAudio
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Old 29th September 2012, 08:05 AM   #1
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Default The dreaded long throw question

Hi all.

I notice this question has been asked before, 4 years ago and still hasn't had a reply:
long throw or zoom lens attachment

So I thought I'd ask a similar question to see if there is anybody out there...

I recently bought a projector that will remain un-named as it has got a lot of bad reviews (Abus HD-12 Pro) which I actually like, except for the racket of the fan. and its inability to decrease image size except by moving the projector back and forth.

Yes, I should've bought a more expensive one, but my redundancy package wouldn't go that far..

All I want to do is move the thing back about a metre (into a convenient cupboard with a window - which I have yet to cut out, but keep the projected size the same. Long throw lenses are over 1000 which is a bit harsh as the projector cost less than 200. It uses a 5 inch LCD screen and all I can tell you about the lens is that it has a 68mm diameter at the front - I haven't found any info on focal lengths etc. on the web to date.

I have the projector 3.18m from the wall which gives a projection size of 100 inches (2.54 metres) diagonal. I want to move it back to 4.16 metres and keep the 100 inch projection size, the size would be 130 inches (3.3 metres) diagonal at that distance.

Not knowing a thing about lenses, is there anything in the Optics Shed that I could fit on the front or the back of the existing lens that won't put my mortgage payments in jeopardy? Could I alter the existing lens with a hacksaw, hammer and Duct tape? Would a chat with a friendly optician (if I find one) help?

Is there distances inside the projector I need to measure to help someone come up with a solution? Will a picture help? Is the Earth flat? Will I ever get another job that'll pay for a long throw lens?

Any (polite) suggestions would be appreciated.

All the best,
Fitch.
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Old 24th February 2013, 02:31 AM   #2
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Default no takers

Looks like this thread won't get answered either....
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Old 24th February 2013, 02:46 AM   #3
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Interesting question, but this part of the forum gets so little traffic, you know.
As a projectionist myself, I know that longer lenses - within reason - are easier than short ones. Fortunately for me, I can just pick what I need off the shelf.

I wonder if you couldn't play a bit with multiplier lenses meant for cameras? They can be found online for reasonable prices, or maybe you know someone who can lend you one?
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Old 24th February 2013, 02:54 AM   #4
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I do actually have a x2 converter for my canon SLR, of course it's only a 50mm lens so I presume I would be looking for something a tad wider. Is that the sort of thing you mean?
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Old 24th February 2013, 04:06 AM   #5
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Yes, the 1.5X or 2X converters. It's worth a shot if you can find a 68mm or larger. Or just test the one you have.
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Old 25th February 2013, 11:47 AM   #6
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Default Which way?

OK. Do I put the converter in front of the projector, or do I put it between the LCD ands the lens,.
Which way round do I put the converter?
Sorry, but I'm quite hopeless at this sort of thing..
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Old 26th February 2013, 04:06 PM   #7
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Put it at the front of the lens. Put the ring thread toward the lens, just as you would with a camera. Let us know what you find!
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Old 26th February 2013, 10:43 PM   #8
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Default Oops!

Just got the converter out of the bag, only to find the rear cap is stuck solid. Even tried unscrewing it with a jam jar opener. Won't budge. Will have to take it to a workshop and try to prize it off, so will be a few days before I can answer.
Cheers!
Fitch.
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Old 6th March 2013, 03:43 PM   #9
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Any luck with it yet?
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Old 6th March 2013, 10:41 PM   #10
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I'm going to break the damn thing if I try any more. Will take it to the physics department in the University where they can mount it in a chuck and use a strap wrench on it, problem is, I've gone down with the dreaded lurgy, so am tucked up in bed for the next few days.
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