Thread: I call Hot Rod Cameras Bluff with a $10,000 Bet (for Sharpest PL RF for Komodo)

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  1. #231  
    Quote Originally Posted by Phil Holland View Post
    This is a fascinating statement that I don't think many optical engineers would agree with, PHD or not.

    Longer lenses typically would observe less of the behavior due to typical designs. But I'd say it's pretty observable 85mm and wider in most cases.

    There are lenses that exhibit less of an issue when things are off, mainly due to telecentricity, but still measurable divergence.

    Grabbing something like an 18mm Master Prime, this is pretty easy to test. Grabbing something a bit more forgiving less so.

    One of the reasons vacuum plates were used in 70mm camera heads was to combat the image plane from being uneven, which was/is visible in projection when something goes wrong, i.e. uneven focus across plane. Less of an issue on smaller formats as the rigidity of film stands up better, but nonetheless a rather visible issue.

    I only know about this due to working on those style of productions and using the Solitaire with 70mm head featuring a vacuum within the gate and the critical nature of ensuring the flange was on point. Same thing done actually with the attenuators in laser recorders to achieve critical focus.

    All optics. All important.

    Phil a film printer is something completly different. You project an image onto a flat filmstrip. The whole image goes soft if its focus is not set correctly. Same goes for your film projector at home. When you dial in focus on it its important that the focus plane of the projector is aligned with your projector screen or the whole image goes soft.

    But for a film camera that is aimed into a 3 dimensional scene with objects at different distances to camera the main thing that happens when back focus is altered is that the focus plane moves back and forth trough that scene.. where ever the focus plane lands when bacfocus is altered things will be sharp.
    So a small error in back focus just push the focus plane into to or out of the scene. You also get a small alteration to the actual focal length of the given lens and yes the "physical camera" move sligthtly in Z direction, as the nodal point for the lens gets pushed. And yes its more critical the shorter the focal length is and your lens start to get other deviations when it goes to the extremes.
    If you push the lens a lot towards the sensor you will have increased vinjetting etc. and If you pull it out/ away form the sensor you get a longer focal length and sure if you double the nodal / backplane distance so you make your 50mm lens into a 100mm lens you also loose a lot of shapness, exposure etc as you then only use a fraction of the projection of the lens.


    Playing with a swing shift lens or a lensbaby or such gives a good view of how it works.



    Regarding vaccum plates and uneven focus on 70mm cameras. Such plates as I understand was mostly implemented to control gate weave, basically keep the film strip at a constant distance. Same with pin registered cameras and printers that had pins to control the X/Y movements of the film strip. They also have a feeding foot that clamp down on the neg pushing it against the back plane for each frame. The bigger negative and the more / faster it has to move between each frame the more it flaps around in there which cause problem.

    But yes, projecting a allready shot image onto a flat surface is not the same as aiming a camera into a 3 dimentional world.
    Björn Benckert
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  2. #232  
    Senior Member Jacek Zakowicz's Avatar
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    What's a warped film plane have to do with lens back focus? First flatten the film plane. Back focus change on the lens is not going to fix it.
    Jacek Zakowicz, Optitek-dot-org, jacek2@optitek.org
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  3. #233  
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    It feel like I’m in some surreal alternate reality.

    FFD / lens collimation doesn’t affect the lens performance other than

    1. Can it hit infinity ?
    2. Do the witness marks line up as intended?

    Talk of lenses not performing or being optically compromised is bunk. If the FFD is a “bit” out then all the happens is the SAME lens performance for the focus range that it CAN hit.

    Inferring otherwise is FUD.

    Also, for those of you who love Contax mount Zeiss stills lenses, not many seem to appreciate the cameras they were designed to be used with.

    Pre Digital, I used (and still shoot) Contax cameras. They made this very under appreciated and unknown camera, the RTSIII.

    Along with some eyebrow raising features at the time (1/8000 top shutter in 1990 was a feat), 5 fps drive built in, dual battery power options, pre flash metering and a frame counter in the EVF itself.

    One unique feature was a vacuum ceramic pressure plate.

    So it’s certainly be done for cameras before and not just “moving” cameras.

    https://camerapedia.fandom.com/wiki/Contax_RTS_III

    JB

    Lover of Contax and owner of many bodies. If you buy and RTS3 make sure you check that the lcd isn’t bleeding, a common fault over time.
    John Brawley ACS
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  4. #234  
    Senior Member Adrian Jebef's Avatar
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    I think the BIG distinction here is "does the lens hit infinity" and if so is it dead on per spec rather than very close. I have seen a LOT of wide lenses that are "close enough - good enough" and are therefore considered on spec however under more careful review there are noticeable performance losses. And again this could be an issue with the camera body mount and/or the lens itself.

    This thread is a bit all over the place. There is a lot of chatter about the ability to get to PL spec and once there an affirmation that performance and collimation is exact. I agree with all of that. But it seems the OP was making a simpler argument: any PL mount adapter that gets closer to collimation spec out of the box will outperform any other adapter that doesn't. The responses on this thread point out one of the big divides here on Reduser: the minority of users that work on and have access to high-end, international, large-scale budget productions and the majority of users that simply don't have access to that level of production. This is not a judgment simply an acknowledgement that there are a lot of Komodo users out there that don't have access to or training in proper collimation. Therefore any out of the box PL adapter that is closer to spec will outperform any PL adapter that is not; irrespective of the later ability to collimate to spec.

    IMO knowing that collimation is an issue that needs addressing is most of the battle.
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  5. #235  
    Senior Member Jacek Zakowicz's Avatar
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    I think we need to clear up one thing- the typical back focus error has zero effect on a spherical lens optical performance, i.e. resolving power, contrast, field curvature, lateral dispersion, longitudinal dispersion, coma, spherical aberration, field curvature, astigmatism, etc. None whatsoever s far as the film makers are concerned.
    Jacek Zakowicz, Optitek-dot-org, jacek2@optitek.org
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  6. #236  
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    Quote Originally Posted by Jacek Zakowicz View Post
    I think we need to clear up one thing- the typical back focus error has zero effect on a spherical lens optical performance, i.e. resolving power, contrast, field curvature, lateral dispersion, longitudinal dispersion, coma, spherical aberration, field curvature, astigmatism, etc. None whatsoever s far as the film makers are concerned.
    Exactly.

    JB
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  7. #237  
    Moderator Phil Holland's Avatar
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    Quote Originally Posted by Jacek Zakowicz View Post
    I think we need to clear up one thing- the typical back focus error has zero effect on a spherical lens optical performance, i.e. resolving power, contrast, field curvature, lateral dispersion, longitudinal dispersion, coma, spherical aberration, field curvature, astigmatism, etc. None whatsoever s far as the film makers are concerned.
    Looks like I need to post some examples. "as far as film makers are concerned", most interesting statement that made me actually angry today.

    Be back in a few days when I'm done shooting I guess.
    Phil Holland - Cinematographer - Los Angeles
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  8. #238  
    Senior Member Adrian Jebef's Avatar
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    Quote Originally Posted by Jacek Zakowicz View Post
    I think we need to clear up one thing- the typical back focus error has zero effect on a spherical lens optical performance, i.e. resolving power, contrast, field curvature, lateral dispersion, longitudinal dispersion, coma, spherical aberration, field curvature, astigmatism, etc. None whatsoever s far as the film makers are concerned.


    is focus / sharpness not part of a lens optical performance? a lens is made to focus an image on a flat 2D plane. if that focus is incorrect the image's optical performance is compromised. back-focus / collimation has hella effect. a lens is made to go on a camera. it is not an end unto itself.
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  9. #239  
    Senior Member Jacek Zakowicz's Avatar
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    Quote Originally Posted by Adrian Jebef View Post
    is focus / sharpness not part of a lens optical performance? a lens is made to focus an image on a flat 2D plane. if that focus is incorrect the image's optical performance is compromised. back-focus / collimation has hella effect. a lens is made to go on a camera. it is not an end unto itself.
    Focusing is something easily achieved with a part of the lens called the focus ring. I'm surprised I needed to explain it here. And no- it is not optical performance. It's is a mechanical adjustment.
    Jacek Zakowicz, Optitek-dot-org, jacek2@optitek.org
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  10. #240  
    Senior Member Jacek Zakowicz's Avatar
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    Quote Originally Posted by Phil Holland View Post
    Looks like I need to post some examples. "as far as film makers are concerned", most interesting statement that made me actually angry today.

    Be back in a few days when I'm done shooting I guess.
    Haha politics are definitely your forte. Lets see the examples. And no- defocused images will not cut it
    Jacek Zakowicz, Optitek-dot-org, jacek2@optitek.org
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