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Spherical Lens Question


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#1 Dave Campbell

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Posted 21 April 2009 - 04:41 AM

:blink: I've seen the term "spherical lens" in a few 2 perf Techniscope threads. Does this mean any lens that is not anamorphic? Are most or all primes and zooms spherical lenses? Are there non-spherical lenses?
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#2 Adrian Sierkowski

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Posted 21 April 2009 - 05:18 AM

That is my general understanding. Think of it this way, a Spherical lens projects an image circle where and an anamorphic projects an oval (I think in any cast a squeezed image.)
Pick up Cinemtography: 3rd Edition it has a great little graphic showing how each works:
http://www.amazon.co...d...9073&sr=8-1
and is quite a pleasant read.
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#3 Martin Solvang

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Posted 21 April 2009 - 02:43 PM

Hey,
a spherical lense is considered a simpler lense in optics as it consist of a part of a full sphere or a sylinder.
The problem with spherical lenses incorporated into optics in general are that they produce optical aberrations,
witch can for example result in loss of contrast and resolution, often towards the outer parts of an image.

Aspherical lenses are dificult to produce as they need a more hands-on aproach in production (a least when they are made of glass..)
The lens will bend certain parts of the image, and reducing the optical aberrations that we all hate in cheap zooms, older zeiss primes etc.

Another great thing is that an aspherical lens may incorporate the optical qualities of many spherical lense elements, making the acctual lense
mounted on the camera, lighter and with less breating when focusing.
The new master prime series from Zeiss has been put together with aspherical lense elements and produces super sharp images (to sharp maybe..?)
the only problem is that they are much more expensive to produce, bye and in our case - rent.
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#4 Martin Solvang

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Posted 21 April 2009 - 02:52 PM

aspherical = non-spherical

I generally think it´s important to differ between
lenses - glass or plastic elements ground or moulded to a spherical/aspherical shape based on the prinsipals of convex, concav or combinations of both.
optics - sets of lenses
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#5 Tom Jensen

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Posted 21 April 2009 - 03:07 PM

The lens will bend certain parts of the image, and reducing the optical aberrations that we all hate in cheap zooms, older zeiss primes etc.


Cheap zooms yes. Older Zeiss primes, not me. Zeiss glass is great. The problem with the older lenses is in the mechanics. The threaded brass rings in the focusing mechanism have a tendency to wear.
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#6 Adrian Sierkowski

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Posted 21 April 2009 - 03:11 PM

Martin, while all of that is true, for optics, at least in my own experience, in terms of cinematography, spherical lenses v anamorphic lenses are just the processes, even if the lens itself is aspherical. Just that when you shoot say 3-perf for a 2:40 extraction the cinematographic process is referred to as "spherical." At least that's what I got the question was asking-- more nomenclature as opposed to actual science behind it.
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#7 Martin Solvang

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Posted 21 April 2009 - 03:29 PM

Adrian, guess I understood the question differently :D
I really don´t think it´s that scientific, in a world where most of us will never shoot
anamorph (in Norway f.ex), the understanding of optical aberrations in all it forms are
important and fun.
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#8 Adrian Sierkowski

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Posted 21 April 2009 - 03:32 PM

If only our high school science teachers could hear us now speaking about the fun of science ;)
It is quite sad that many of us will never shoot anamorphic (though with some new D-cinema cameras... we can).
Your explanation is quite simple (considering the science involved) and certainly was a nice read for me here.
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#9 Dave Campbell

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Posted 21 April 2009 - 03:46 PM

Thank you all for your answers to my query. Adrian, I'm going to pick up Cinematography-3rd edition. I'm still not sure which lenses are spherical. For instance, I'm holding in my hand an Angenieux 10-150 for my 16mm camera. Would this lens be considered spherical? Can any of you give me some more examples of spherical and non-spherical lenses? Please - not too technical, remember, this is the idiot section of the forum. Thanks.
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#10 Adrian Sierkowski

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Posted 21 April 2009 - 03:48 PM

If you're talking about the process, you would refer to it as spherical as it's not an anamorphic lens, though the lens itself is probbly n aspherical lens.
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#11 Tom Jensen

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Posted 21 April 2009 - 04:00 PM

Thank you all for your answers to my query. Adrian, I'm going to pick up Cinematography-3rd edition. I'm still not sure which lenses are spherical. For instance, I'm holding in my hand an Angenieux 10-150 for my 16mm camera. Would this lens be considered spherical? Can any of you give me some more examples of spherical and non-spherical lenses? Please - not too technical, remember, this is the idiot section of the forum. Thanks.


Think of a big cone of light entering the lens it flips upside down at the nodal point and is projected out the back of the lens. The reason that the image is a rectangle and not a circle is because you have an aperture plate that blocks or crops out the rest of the image. If you were to do the same the thing to an anamorphic lens which is not spherical (round) your image would be squeezed in the middle. It goes onto the film squeezed and is projected by a projector with a lens that un-squeezes the image so it now appears normal yet wider. Don't over think this. Take the 10-150 and look through the end of it. The image should be round, spherical. Most lenses are spherical.
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#12 Martin Solvang

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Posted 21 April 2009 - 04:34 PM

Tom,
I agrea, the Angenieux is most probably spherical, the new Optimos are aspherical as far as i know,
but the 10-150 is from an age where production of aspherical elements was difficult.

I found an interesting thing on the nodal point(s) not being what you describe TOM,

check it out: http://doug.kerr.hom...Pivot_Point.pdf

The only reason we think the nodal point is where the image is flipped upside down (and where we are mislead to tilt/pan the cam on f.ex the F7)
is because "the entrance pupil" where i supposedly acctually happens,
sometimes/often coencides with on of two nodal points.

These are not my thoughts, I just found them interesting, having believed for years I was using the right term...
OK,
now I feel like a nerd.

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#13 Dave Campbell

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Posted 21 April 2009 - 04:46 PM

Thanks Tom. That answered it for me. Adrian, the process is spherical, but the lens is aspherical? I'm going to have to do some of that reading that you suggested. Thanks all.
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#14 Tom Jensen

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Posted 21 April 2009 - 05:05 PM

I'm just trying to keep it simple. Don't make me dust off my old optics books. :blink: :P ;):blink:
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#15 Tom Jensen

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Posted 21 April 2009 - 05:33 PM

All my lens books are in the garage burried. Disregard nodal point. I can't remember exactly what it is called. I'm lucky if I remember what I had for breakfast, if I ate at all. The one important thing that you students need to remember is you don't have to know everything. You have to know a lot that's for sure. Don't look at the camera, look through the camera. You are making art, not science. Science is just another tool. Think more about the quality of light around you. Look how it hits people's faces. Your light meter will tell you quantity. Sometime people get so wrapped up in the technical side they miss the art.
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#16 John Brawley

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Posted 21 April 2009 - 07:02 PM

:blink: I've seen the term "spherical lens" in a few 2 perf Techniscope threads. Does this mean any lens that is not anamorphic? Are most or all primes and zooms spherical lenses? Are there non-spherical lenses?



I think there are two issues being discussed here.

In Cinematogroahy lingo, If you are NOT shooting anamorphic (in-lens optical squeezing), then you are said to be shooting spherical, no matter if it's 2 Perf, 3 perf or 4 perf.

As a separate note, some lens designs (be they anamorphic or not) have aspherical elements WITHIN the lens itself which correct for OTHER optical issues or make it possible to have smaller and lighter lenses.

If you look at an aspherical element from the side, it's not a concave or convex shape, but changes across it's surface. it may still produce what tom calls a spherical image when you look from the rear.

This hasn't got anything to do with the fact that it's anamorphic or not, which is a choice not a correction. The anamorphic element in an anamorphic lens is separate to any aspherical elements it may have.

jb
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