measurement in mm lens mount to sensor plate BMPCC 4K ?

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aknittel

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measurement in mm lens mount to sensor plate BMPCC 4K ?

PostMon Apr 12, 2021 6:53 pm

Trying to determine the nodal point with a MEIKE cine prime lens. It appears as though I FIRST need to know the measurement in mm from the lens mount to the sensor plate.

Where is this published?

Then I can determine where the optical sensor of the lens is and add the measurement I just asked for.
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Re: measurement in mm lens mount to sensor plate BMPCC 4K ?

PostMon Apr 12, 2021 9:21 pm

If you’re looking for the flange focal depth for Micro Four-Thirds I believe it’s 19.25mm.
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Re: measurement in mm lens mount to sensor plate BMPCC 4K ?

PostMon Apr 12, 2021 10:04 pm

Yes and Thanks much!

Flange focal depth (FFD) is the distance from the shiny metal flange of the camera's lens mount to the imaging sensor.

Now I believe I need to get the lens optical center to the flange measurement and add that and the FFD and that should give me true optical venter (nodal point) of the camera/lens combination.
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Re: measurement in mm lens mount to sensor plate BMPCC 4K ?

PostTue Apr 13, 2021 8:05 am

aknittel wrote:Yes and Thanks much!

Flange focal depth (FFD) is the distance from the shiny metal flange of the camera's lens mount to the imaging sensor.

Now I believe I need to get the lens optical center to the flange measurement and add that and the FFD and that should give me true optical venter (nodal point) of the camera/lens combination.

Why do you need this information? There are infact 2 'nodal' points on most lenses so perhaps you mean the point of no parallax? This can be worked out using methods employed for panoramic photography and readily available on youtube etc.
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Re: measurement in mm lens mount to sensor plate BMPCC 4K ?

PostTue Apr 13, 2021 9:54 pm

Thanks - I DO mean the point of no parallax, since there is only ONE mark on the lens for the camera its mounted on required for a reference point.

Yes I DID see rather complicated setups requiring at the very least a $129 nodal pan rig all the way up to a $700 rig which is ridiculous for my use case. I'm not doing nodal panoramic photography, or even performing nodal pans.

The VES handbook started me off on a tangent considering triangulation measurements (tilt, height, distance to subject, ground baseline) for recording on-set camera measurements for matchmoving studio footage with live plate background when compositing.

I'm debating whether modern photogrammetry camera tracking has enough accuracy for what I'm doing and chasing this is a red herring for me (or anyone else).
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Re: measurement in mm lens mount to sensor plate BMPCC 4K ?

PostTue Apr 13, 2021 9:57 pm

Actually the correct term for what I'm looking for is "Entrance Pupil" of which there is only ONE.
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Re: measurement in mm lens mount to sensor plate BMPCC 4K ?

PostWed Apr 14, 2021 1:28 am

aknittel wrote:Trying to determine the nodal point with a MEIKE cine prime lens. It appears as though I FIRST need to know the measurement in mm from the lens mount to the sensor plate.

Where is this published?

Then I can determine where the optical sensor of the lens is and add the measurement I just asked for.


If you’re trying to go nodal then it’s based on where the film plane is, and not to do with the lens.

The film plane on those cameras was flush with the face of the body itself.

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Re: measurement in mm lens mount to sensor plate BMPCC 4K ?

PostWed Apr 14, 2021 2:06 am

As much as I honour your knowledge in all things cinematography, John, in this case I dare to contradict.
Having done a lot of panoramic photography (and using one of those expensive rigs) the nodal point was always somewhere in the lens and we had to test it out for each lens individually.
It should be something like the point where the rays are crossing, isn't it?

But while we were using more expensive ones due to vertical mounting of the camera, a cheap mount for moving the camera back and forth with some sort of scale should suffice to find that point. That is, if you can make sure to have the lens centered over the mounting point laterally.
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Re: measurement in mm lens mount to sensor plate BMPCC 4K ?

PostWed Apr 14, 2021 4:45 am

Uli Plank wrote:As much as I honour your knowledge in all things cinematography, John, in this case I dare to contradict.
Having done a lot of panoramic photography (and using one of those expensive rigs) the nodal point was always somewhere in the lens and we had to test it out for each lens individually.
It should be something like the point where the rays are crossing, isn't it?



Always happy to be corrected and proven wrong.

I'm guessing for practical purposes in the work I've done it's always been assumed to be at the film plane itself. (for panning, tilting etc.)

Now I'm going to have to go look it up.

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Re: measurement in mm lens mount to sensor plate BMPCC 4K ?

PostWed Apr 14, 2021 5:12 am

Uli Plank wrote:As much as I honour your knowledge in all things cinematography, John, in this case I dare to contradict.
Having done a lot of panoramic photography (and using one of those expensive rigs) the nodal point was always somewhere in the lens and we had to test it out for each lens individually.
It should be something like the point where the rays are crossing, isn't it?

But while we were using more expensive ones due to vertical mounting of the camera, a cheap mount for moving the camera back and forth with some sort of scale should suffice to find that point. That is, if you can make sure to have the lens centered over the mounting point laterally.


The quick version is I was wrong, it is NOT the film plane, but it also seems there can be more than one nodal point.

"Two additional cardinal points are the front and rear nodal points (N and N′) that define the location of unit angular magnification for a focal system."

https://spie.org/publications/fg01_p11_ ... ints?SSO=1

I think though that in most functions for shooting product and drama, the film plane can be considered "close enough" depending on what you're trying to do of course. I feel like I've used nodal head before and the assumed nodal position was the film plane.

Many times we use "nodal" heads like an Arri geared head or something like a Ronford F7 and these usually function by having the film / sensor plane itself be the nodal point around which the camera moves.

Most grips would set these heads up assuming the film plane was the nodal point.

https://www.cartoni.com/products/fluid- ... lambda-50/
http://www.ronfordbaker.co.uk/products/ ... s/atlas-7/

If you were trying to shoot stills with panoramic stitching for example, then it might require the true precision of the lens nodal point.

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Re: measurement in mm lens mount to sensor plate BMPCC 4K ?

PostWed Apr 14, 2021 8:02 am

aknittel wrote:Thanks - I DO mean the point of no parallax, since there is only ONE mark on the lens for the camera its mounted on required for a reference point.

Yes I DID see rather complicated setups requiring at the very least a $129 nodal pan rig all the way up to a $700 rig which is ridiculous for my use case. I'm not doing nodal panoramic photography, or even performing nodal pans.

The VES handbook started me off on a tangent considering triangulation measurements (tilt, height, distance to subject, ground baseline) for recording on-set camera measurements for matchmoving studio footage with live plate background when compositing.

I'm debating whether modern photogrammetry camera tracking has enough accuracy for what I'm doing and chasing this is a red herring for me (or anyone else).

You just need a rail such as arca swiss on a plate to move the camera in one axis and not a complicated or expensive rig. The no parallax point or point of perspective is the correct coordinate for photogrammetry / 3d use. Not sure why you need this though in a photogrammetry setup unless you are doing close up shots of objects or super accurate compositing. Even if you had it you still have to position the camera accurately in XYZ and roll, tilt and pan.
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Re: measurement in mm lens mount to sensor plate BMPCC 4K ?

PostWed Apr 14, 2021 8:03 am

Yes, the difference only shows when foreground objects are pretty close.

We used to make VR tours for the upper-class hotel industry, but even there rooms can be small and are usually shot with wides ;-)
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