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Discussion Starter · #1 ·
Hi all,

After my introduction I wanted to tell you about a little project I've been working on for a few weeks now.

I know this section is for anamorphic projection lenses, but I'm hoping to use the same basic principle for exactly the opposite: recording anamorphic using HDSLR cameras.

There're a few commercial options out there, but I'm the DIY kind of guy and I'd love to build the adapter myself. I've already contacted a few providers and custom parts builders, but first of all I need to start with the basics.

I know there're 2 different approaches: prisms and cylindrical lenses. I want to go for the last option because I'm specially worried about aberration and, from what I read so far, cylindrical lenses are much better handling it.

Now comes the hardest part: optics. I know the basics, but I came to a point where I'm having a really hard time figuring out what to do next.

As far as I know, I'd need a negative cylindric meniscus on the outer front and a positive one in between so focal length is cancelled and it just deforms the incoming image. Also I know I have to stretch the horizontal plane by 1.33x since the camera sensor is not 4:3, but 16:9 and that would be the way to create a perfect 2.39:1 image in post. The last part would be of course to build it big enough to avoid vignetting.

Now, my real problem comes when trying to translate that info into a proper diagram for the optics company, so I really hope someone here can help me out with that or at least point me in the right direction.

Thanks for everything.
 

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I'm not the optics guy at work, but we do a lot of camera, lens, filter, laser and fiber optics stuff. So I get exposed to that every day.

We use Edmund Optics and Thorlabs for a lot of our stuff. Edmund has some great resources for lens design, what types of lenses do what, problems like chromatic aberration and off-focus. I've never built a lens through them, but I've used their learning resources a lot.

We usually just buy simple filters and collimating lenses through them. Never anything like a cylindrical lens. Hopefully you can find some good info there, though.

Welcome to the Shack!
 

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......... Also I know I have to stretch the horizontal plane by 1.33x since the camera sensor is not 4:3, but 16:9 and that would be the way to create a perfect 2.39:1 image in post...........
Can you run that by me one more time? Are you trying to capture a 16:9 aspect ratio on a 4:3 format camera? How does the 2.39:1 come into play (maybe you're talking about capturing a 2:39 image on a 16:9 camera)???

You're going to use two cylindrical lenses as you described to change the horizontal magnification (to less than 1) for a camera. If you have cemented achromatic lenses designed for this, it will be very expensive, but you can do it with relatively inexpensive cylinder optics from an eyeglass shop. These won't be color corrected, but the results might be acceptable given the low magnification and the use for an HD camera. Please clarify your quote.
 

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Discussion Starter · #6 ·
I think I didn't explain myself properly.

What I was trying to say is that this adapter doesn't have to do an approximate 2x stretching like a standard 4:3 to 2.39:1 conversion. Instead of that, it has to fit that 2.39:1 frame inside a 16:9 sensor. How? By making the horizontal field of view wider by 33%. Here's a visual explanation (didn't work, I'm attaching the image).


You say I can do that with relatively inexpensive cylinder optics. I'd love to explore that option as well, although at first I was thinking about having them custom made, but I need to know the actual diagram and, most important, the focal length of the lenses needed. Could you please help me with that?

Thanks a lot.
 

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Try this configuration. It will get you really close to the conversion you want with a couple of meniscus cylinder lenses. You should be able to go to an optical lab (eyeglass lab) and get these in uncut versions which will give you some diameter to work with (the negative lens requires the largest diameter that you can obtain but you might want the diameter of the positive lens reduced somewhat). The curves shown (exaggerated for illustration) are only in one dimension and the lenses are flat in the other (cylinder curves). I listed the diopter values because that's what they're usually used to working with, but I also included focal lengths in case your need that info. Again, there is no chromatic correction in this, but the low power will probably yield fair to good results. It's also very important to get the cylindrical axes of both lenses aligned when you mount them. You might need to trim the spacings for best focus (at infinity) and if you shoot near objects, the spacing needs to change to accommodate this (this lens has a focus adjustment in addition to your regular lens).

Unless you have the lenses coated, you could have a problem with reflections, but you did mention lens flare!

If these are used on a projector, the image will be expanded along the cylinder axis (you're going to do that in post by digitally by shrinking the image vertically).
 

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Discussion Starter · #10 ·
Well, first of all, thank you very very much RBTO!! I'll search for eyeglass labs and see what I can find. Also, just out of curiosity, I'll ask my initial providers for prices on achromatic versions of those lenses.

And I'll start designing a box.

Thanks a lot again.
 

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You're quite welcome.
You might consider using an old lens mount that has a helical so you can focus the anamorphic. A bellows arrangement will also work (fixed position for the rear, and rack & pinion to move the front). The main thing is not to have any relative rotation between the two when focusing.
Let us know what you learn.
 

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Discussion Starter · #12 ·
Yes, my initial concept included an extensible two-parts box for focusing purposes.

Thanks again!!
 

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Discussion Starter · #13 ·
Ok, I've sent mails to a few online optical labs and I'll check on my nearest optician on monday to see if he can provide me with the lenses needed.

Do you recommend any particular site? Just in case.

Thanks.
 

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That's where it might get a little sticky. These lenses are not "off-the-shelf" variety so they need to be custom made. Be ready for sticker shock when dealing with most manufacturing optical sources (particularly if you want achromatic versions). I think the optician may be the best way, but even with that, you might need to do some footwork to find one that can custom make the cylinder lenses. These are not the usual correction anyone would use for eye problems!

Here are a couple of sources that might be able to help you:

http://www.toweroptical.com/cylindrical-lenses.cfm

http://www.knightoptical.com/php/showCatPage.php?cat=24

Good Luck in your search.
 

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Discussion Starter · #16 ·
Thanks again RBTO, actually I was talking about online opticians instead of optical equipment companies and manufacturers because I know it should be easier to get results from the former. As I said, I checked like 30 different sites and mailed the ones offering uncut lenses. I just wanted to confirm I wasn't bypassing an easy one. Actually I found one giving me the full price online and ready to order. It was about $260 for 4 lenses (2 of each just in case) but I want to get responses from a few more before ordering.

About Surplusshed, I knew about it and I'll problably use them if I need achromats.
 

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I'm sure people buy the old 35mm anamorphic lenses off eBay for filming and then find some way of adapting them for their cameras. They go for very little money (sometimes less than $100 for a cylindrical lens. The 35mm projection lens attachments have a 2x horizontal stretch to take a 4:3 image to 2.37:1.

It will of course then need a vertical stretch to play it back. If you just want it to be letter boxed, then it may be easier to shoot with a regular wide angle lens and then crop it after. An even easier solution is to buy or make an anamorphic mask which crops the shot while filming.

Some of the old anamorphic attachments are variable so you can control the stretch if you any 1.33x instead of 2x to take a 16:9 image to 2.35:1 or a 1.5x to take 4:3 to 16:9.
 
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