Sankor 16C Advice wanted

[Darren Tansey]

Hello, I have the chance to purchase a Sankor 16C Anamorphic lens at a good price. I intend to use it for my Super 8 and 16mm projectors. I've been informed by the seller that it has a smaller rear diameter than a 16D lens, but it's still ok for Super 8 / 16mm projection.

I've also heard the opposite, that a 16C has a larger rear diameter than a 16D, so I'm not sure what is correct. I understood that a larger rear diameter is better in terms of reducing vignetting. I'm a little confused, so any advice would be much appreciated, many thanks, Darren

[Steve Klare]

Hi Darren,

If nothing else, I have the 16C and can testify it does just fine for Super-8, but I haven't had the experience of trying 16mm 'scope so far.

(-not that I'm against it!)

-but I've never had trouble with vignetting with the 16C with Super-8 and a zoom lens with a maximum focal length of 25mm, so if my assumptions are good, a typical 50mm lens used with 16mm film shouldn't have any troubles either.

OK, I'm going to go out on a limb here and try some math: (-and someone please check it!)

Internet 'sez a 16mm frame is 10.26x7.49mm. Pythagorean theorem 'sez that's 13.7mm diagonal.

At one focal length forward, the picture will be the same size as the frame, but flipped right side up, so 13.7mm diagonal once again.

My caliper 'sez the rear element of a Sankor 16C is 33mm across, so enough room for 2.6 of these 13.7mm frames as long as everything is aligned perfectly, so vignettting should begin when the rear element is at least 2.6 focal lengths forward of the middle of the lens, so 5.2 inches with a 2 inch prime lens and you should be safe with anything closer. (This sounds doable to me)

(-Thoughts? It's been a long time since I learned optics!)

[Steve Klare]

I actually had the chance to try this out last night and the news is good.

I put my Sankor 16C in front of my 16mm machine and had no trouble getting an image through the lens without vignetting. The even better news is that I run with a 1.5 inch lens because the 2 inch the machine came with makes the image too small on screen at the throw that I have, so it would be that much easier with a 2 inch lens because the magnification there is less and the beam we want to put through the anamorphic is that much narrower.

I have a correction of the calculation I did yesterday above: I did more research and I found a formula for "L", the throw length required to get a projected image of a certain size: L=(W_image/w_object+1)*f, Where the "W"s are the width of either the image or the object ("film" to us) and "f" is the focal length of the lens. If we say that the back of the anamorphic lens can accept an image up to 2.6 times the size of the one on the film, and we have a 2 inch lens, then the distance before we start to get vignetting should be (2.6+1)x2 Inches=7.2 Inches. This seems an easy distance to stay within.

[Darren Tansey]

Hi Steve, thank your very much for your extremely detailed information. It's good to know that you successfully tried your Sankor 16C in front of your 16mm machine, and didn't experience any vignetting. I much appreciate your help with this and I'm confident that the 16C will do the job for me. Thanks and all the best, regards Darren

[Steve Klare]

If you find one at a livable price, you should be all over it! (They can go for a LOT these days!)

Just by being at the right place and time (twice), I got a 16F and then a 16C much later, and pretty reasonable too.
.

I'm good to go!