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Anamorphic and Spherical Lens Focusing

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  1. Sep 8, 2014 #1
    New to the forum but stumbled upon this and thought it might be beneficial to query more scientifically minded individuals. I am a filmmaker and use a variety of lenses to acquire certain looks. One of which is anamorphic cinematography. (http://www.red.com/learn/red-101/anamorphic-lenses) Expensive ($40K and up) anamorphic primes (anamorphic elements and spherical combined into a single focusing lens) are designed to work with single focus. As a cheap work around, indie filmmakers began purchasing projection lenses (http://petapixel.com/2014/05/07/shooting-anamorphic-lens-dslr/) and using them in conjunction with the prime lens affixed to the body. While it produces the effect, both lenses must be focused. I saw somewhere on the net, where both the anamorphic projection lens and the prime lens were set to infinity focus and optics were attached to focus the two lenses. After all this, my question is, what could be affixed the the front of the lenses to focus both? Apologies if I was unclear.
     
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  3. Sep 8, 2014 #2

    Andy Resnick

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    I think I understand your question, but I'm not sure- do you have an anamorphic attachment already?

    In any case, an anamorphic attachment can be very simple (Brewster prism):
    http://www.directindustry.com/prod/ealing/anamorphic-optical-prisms-29471-843383.html

    to more complicated arrangements of cylindrical lenses:
    http://www.iso1200.com/2012/06/most-amazing-anamorphic-diy-adapter-to.html

    The basic concept is to have a lens with two focal lengths, with cylindrical elements providing additional optical power along one axis. Anamorphic attachments are ideally afocal, so the 'prime' lens will be unaltered along one axis: squares becomes rectangles, circles become ellipses, etc. Since vid-atlantic (http://www.vid-atlantic.com/lensshop) recommends focusing both the prime and attachment, I suspect the attachment is not entirely afocal.

    Does that help?
     
  4. Sep 8, 2014 #3
    Close. I have the anamorphic attachment, a lens that focuses from 1m to infinity. Also attached is a prime photography lens (spherical) directly to the body. In the example I saw online, both lenses were focused to infinity and another set of optics were placed in front to focus both lenses with one focus pull of the new optics. My question is what could elements could be affixed to the front of lens system to focus both singly?
     
  5. Sep 8, 2014 #4
    I guess to clarify, what optics arrangement could be placed in front of the anamorphic lens, which is placed in front of the standard prime that is attached to the camera, to focus both from infinity down to about 1 to 2m and back out to infinity?
     
  6. Sep 8, 2014 #5
    It seems with some intense research, I need two elements that when close together are afocal and when spaced have a power of .6 or .5 diopter. Any ideas?
     
  7. Sep 9, 2014 #6

    Andy Resnick

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    Tough to say- my guess is that the third optical element (the third of: prime lens, anamorph, 'focus controller') will depend on the properties of the other two lenses. My rule (since I'm not a lens designer) is that making the optics more complicated always results in degraded performance.

    Alternative idea: what about detaching the prime+anamorph from the camera body and focus view-camera style with a bellows?
     
  8. Sep 9, 2014 #7
    Thank you for all of the replies! I've been able to narrow down what it is I'm trying to do. As I understand it, focusing both the lens on the camera and the anamorphic to infinity, this produces an afocal block. Mounting a variable diopter in the front allows one to tame the focus back from infinity to something shorter. This is how popular single focus (expensive) anamorphics work. From the constructions I've found, the variable diopter is comprised of a plano-concave and a plank-convex lens that varies the diopter power based on the spacing and the two elements are afocal when touching. I guess my question as it stands now is: Where can I find a formula or the such to figure out the power of the two elements in order to achieve the afocal aspect as well as closer focus?
     
  9. Sep 10, 2014 #8

    Andy Resnick

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    Honestly, I wouldn't recommend trying to 'home-brew' something like that, I'd be surprised if the optical performance of a simple air-spaced doublet would not grossly degrade the imaging performance of your other lenses: field of view, chromatic aberration, coma, ghosts... I do recommend experimenting with what you have, to see if you can achieve the results you are interested in.

    There's a reason expensive lenses are expensive.
     
  10. Jun 30, 2015 #9
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