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Author
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Topic: A lens you need for short throw problem
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Winbert Hutahaean
Film God
Posts: 5468
From: Nouméa, New Caledonia
Registered: Jun 2003
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posted April 26, 2013 02:02 AM
I found several posts mad eby Elyas that he has a problem with short throw projecting in his room resulting small picture size.
I do have the same problem too back home in Indonesia, but since I have been in Canada for 4 years I forgot that problem until Elyas raised it again.
Because I am returning soon, I was thinking to get an enlarger (cine-larger)lens to be used when I am returning home but then accidentaly I found a video camera that is no longer work and has additional wide converter lens.
So I pcik up this lens and put it in front of my ST-1200 installed with f1.1 (12.5 - 25mm) and this is the result:
1. Sony wide conversion lens x0.7
2. Emergency attachment with cellotape
3. Area for screening
4. Screen shot (Tom & Jerry "Texas Tom", Red Fox print)
5. To give you the idea how big is the screening picture, I am standing in front of the screen. I am 175 cm (5 foot 9 inches) yet I still need to raise my hand to reach the top of picture.
This is what I got with my throw distance at 4.8m (15.75 foot)
Projection at 12.5mm (height x width) = 2m x 2.66m (78.74 inches x 104.74 inch)
Diagonal length: 130 inches
Brightness: Decrese by 10% (but then I compensate by switching the light setting to high instead of low)
Sharpness: no change
So now, try to locate unused cameras, they probably the same wide conversion lens that you can use.
good luck!
[ April 26, 2013, 01:03 PM: Message edited by: Winbert Hutahaean ]
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Winbert
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Bill Brandenstein
Phenomenal Film Handler
Posts: 1632
From: California
Registered: Aug 2007
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posted January 13, 2014 10:20 PM
Hmmm... very interesting. A Bell & Howell lens thread is 54mm, while an Eiki is 48mm. So the smaller Sony lenses will vignette badly due to being 25mm or so. Not sure 33mm would be OK either.
So have a look for yourselves. This stuff is dirt cheap, and only 0.45x (no 0.6 or 0.7s, for example) is available from this seller. Here, for example, is a 52mm version close to the B&H size and here is a 46mm version close to the Eiki size. (If I can't find a matching stepping ring, just might have to tape them on.) For an all-international-shipping seller, that's a pretty spectacular feedback score... how bad can it be? For $31 for the pair and free shipping, I might just have to find out. Thoughts, anyone?
Meanwhile, I'd love to also find some 0.6x lenses with at least 40mm rear glass.
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Bill Brandenstein
Phenomenal Film Handler
Posts: 1632
From: California
Registered: Aug 2007
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posted February 24, 2014 04:24 PM
Time for an update. As anticipated, this did not turn out well. First of all, I must credit eBay seller "foto4easy" with good international service and good presentation. Each lens came in a thin white paper box, a plastic pouch with little drawstrings, and has 2 caps, the camera end being a threaded cap. Looks great.
...until putting it in front of the projector or even a camera. There are two problems: these lenses have two detachable elements and are uncoated, so in addition to bad blurring, there is also a great deal of light scatter from reflections. It really fogs the picture. That alone makes it a show-stopper. The other issue is that the magnification is wrong, and far short.
The whole idea here is that a 0.6x lens is supposed to have that amount multiplied against the focal length of a camera's lens. So if your camera is set to 50mm, and you put an 0.5x magnifier in front of it, then 50mm x 0.5 is 25mm, and you end up with a view twice as wide and twice as high. Since smaller focal lengths result in a wider angle, that's why there's an inverse relationship with the "0.?x" number.
In this case, trying this with a measuring tape against both projected image as well as a digital camera on a tripod, these lenses are far short of the 0.45x (over twice as big) they promise, and by my measurements are in the 0.75x-0.82x range. That makes them so far off the mark as to be unusable in that regard also.
I also bought a Sony 0.6x and a Sigma 0.6x. They both measure slightly less magnification than promised, but are close. The Sony looks just like the one posted at the top by Winbert, which means it's suitable for 8mm projector lenses but is too small for even an Eiki 16. The optics are decent. The Sigma is designed for SLR use and is therefore big enough for a 16mm projector. However, keeping the edges in focus is a big problem that I've not found a solution for yet. There's additional testing to be done to ensure that the actual film is flat enough to do this. Still, for 20 bucks it's a good quick solution, but can't compare to the sharpness and quality of a good $$$ prime lens. You get what you pay for.
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