8mm Forum: A lens you need for short throw problem

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Posted by Winbert Hutahaean (Member # 58) on 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 ]

Posted by Elyas Tesfaye (Member # 3356) on April 26, 2013, 02:02 PM:

All I can say is Win for the win [Big Grin]

!!!

You sir, are a life saver n could you please give me an idea on what kind of old video cam to look for to get at this bad boy? I will try n ebay the lens you posted a pic of n keep you posted on progress [Wink]

... Have a great weekend n God bless for now [Big Grin]

!!!

Best,
ET

Posted by Maurizio Di Cintio (Member # 144) on April 26, 2013, 04:08 PM:

Generally speaking all wide conversion attachments will work for the purpose: they must have a factor of .9 or less: for example a conversion factor of x0.5 gives you an image twice as large as compared to using the standard lens.

Sometimes the opposite problem may present itself, i.e. you need a long-throw lens but have a standard one and the image results bigger than the screen: in this case you can use a tele conversion attachment: the Canon C-8 is excellent, with a factor of (if I'm not mistaken) x1.4

Posted by Winbert Hutahaean (Member # 58) on April 27, 2013, 09:47 AM:

Elyas, as Maurizio says, any wide converter lens will do.

Their prices are not that expensive.

For example this one:

http://www.ebay.com/itm/111051078831?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

The shipping cost si only GBP 1.07 (sent from Hongkong).

This lens will even give you much bigger picture since it hasx x.45 (meaning 2.2x bigger than your current size). Mine is only x.7.

Only you need to be aware is the ring size as the above lens is 37mm. If your projector has bigger ring size it will create vignetting on the screen. For your save it is better to find a converter lens with bigger ring size than your original projector lens.

Good luck.

Posted by Elyas Tesfaye (Member # 3356) on April 27, 2013, 11:13 PM:

Win for the win again [Big Grin]

!!!

Only question I have is what ring size really means [Frown]

... Thanks again and hope you're having a great weekend [Big Grin]

!!!

Best,
ET

Posted by Maurizio Di Cintio (Member # 144) on April 28, 2013, 04:25 AM:

It refers to the back element diameter of the attachment: it mustn't be too small or you will get vignetting at the corners of the projected image. Ideally it should be at least as big as the front element of you projection lens, provided you can get as close as the front element; of course the bigger the better...

Posted by Maurice Leakey (Member # 916) on April 28, 2013, 06:04 AM:

Some adapters have a male screw thread which mates with the same size female thread on the main lens. This would be referred to by its overall diameter in millimetres.

There are other adapters which have just a push fit, however, the same measurements would apply.

Providing it will somehow fit, a larger diameter attachment would be OK, but a smaller one would not pass all the image to the screen.

Posted by Bill Brandenstein (Member # 892) on April 28, 2013, 10:27 PM:

The ratio is expressed opposite of what mathematics would imply? So 0.4 is a greater enlargement than 0.7 if I'm hearing you correctly. Hmmm, this is very intriguing.

Posted by Winbert Hutahaean (Member # 58) on April 29, 2013, 08:48 AM:

Bill, this is the mathematics:

1/0.5 (divided by) = 2 times wider

1/0.45 = 2.2

1/0.7 = 1.42

etc

cheers,

winbert

Posted by Bill Brandenstein (Member # 892) on January 09, 2014, 06:26 PM:

Winbert, curious what the exact model number is of the lens you've tried. There are a good many Sony X0.6 model VCL 0625S lenses on eBay and I'm hoping that's the one you're so pleased with. I'd like to give this a try. Thanks!

EDIT: Whoops! I see that you were using an 0.7, not an 0.6x, so it wouldn't match anyway. Worse, the rear element is only 25mm in diameter, and something larger will be necessary.

[ January 09, 2014, 08:00 PM: Message edited by: Bill Brandenstein ]

Posted by Terry Sills (Member # 3309) on January 11, 2014, 11:47 AM:

Winbert
Great tip. I never even considered doing this - even though I have a couple of vivitar tele converter lenses. One is a 1.5 and that reduces the picture size, but the other is 0.5 and as you say it doubles the size of the picture, and with no detriment to picture quality/sharpness. Great for me as I am limited to a short throw. Like you I have just taped the converter to the prime lens for the moment but it works just fine. Thank you so much!

Posted by Bill Brandenstein (Member # 892) on January 12, 2014, 12:13 AM:

The trick I'm trying to wield is to get one large enough to work with a 16mm projector. There are some really cheap ones from China on eBay in an impressive number of sizes, but I can't imagine the image quality could be all that great. More to come.

Glad you gave it a successful try, Terry!

Posted by Terry Sills (Member # 3309) on January 12, 2014, 01:04 PM:

Bill
The lens I have is a Vivitar wide angle lens 0.6 - (not 0.5 as I said previously) and the rear element is roughly 33mm and the ring size 35mm so I would imagine large enough to make it suitable for some 16mm projector lenses with the aid of an adaptor ring. Vivitar are good lenses and not too expensive. I would avoid the ones made in China/Hong Kong though. They sound too cheap to be anything like quality.

Posted by Bill Brandenstein (Member # 892) on 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.

Posted by Bill Brandenstein (Member # 892) on 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.

Posted by Winbert Hutahaean (Member # 58) on April 04, 2014, 01:54 AM:

A very similar lens is now on Ebay UK for GBP 2.99

http://www.ebay.com/itm/Sony-Wide-Conversion-Lens-VCL-0746B-X0-7-/351039918001?pt=UK_Lenses_Filters_Lenses&hash=item51bb9c0fb1

Bill, you may try this one.

Good luck!

Posted by Paul Mason (Member # 4015) on July 15, 2014, 03:41 AM:

I have tried using a 0.45 times macro wide lens converter attached to my Rank Aldis 16mm projector with a F1.6 50mm lens. For some reason the enlargement is only about 1.2 while I was hoping for 2.2 that is equivalent to 40mm lens not 22.5mm. I suspect that the attachment is to far away from the front glass of the lens but has anybody any ideas? This Ebay item is very similar:
http://www.ebay.co.uk/itm/FUJIYAMA-AF-PRO-0-45-WIDE-ANGLE-CONVERTER-LENS-WITH-MACRO-52MM-/290970818727
Many thanks.

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