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Author Topic: how can I find the center of a lens (horizontal and vertical)? for panos..  (Read 4802 times)

Aristoc

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Can you help to decide how to find the center of a lens?

I have the D90 with a Kirk L bracket but the bracket did not come with center markings. I want to make accurate panos and dont really want to eyeball it unless I have to.

The Really Right Stuff L bracket has markings for the horizontal and vertical center of the camera / lens. but my Kirk L bracket does not.

I now that the tripod mount on the D90 is the vertical center. But how then do I find the vertical center?>

Anyone ?

Thank you

you can see the kind of markings I am talking about. here is the RRS L plate which I do not have.




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Aristoc

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Re: how can I find the center of a lens (horizontal and vertical)? for panos..
« Reply #1 on: September 24, 2010, 11:57:29 am »

GOogle just helped me. Point the camera down and look throug the VF and make sure you are pointing straight down at the pano clamp.

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elf

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Re: how can I find the center of a lens (horizontal and vertical)? for panos..
« Reply #2 on: September 25, 2010, 12:18:49 am »

That assumes the camera is registered perfectly on the bracket :) 

Pick up an engineers square and some digital calipers to measure it. (Actually you just need something that is accurate 90 degrees, like a piece of heavy paper)
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Aristoc

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Re: how can I find the center of a lens (horizontal and vertical)? for panos..
« Reply #3 on: September 25, 2010, 10:30:48 pm »

I'll try it but then I will need to mark the L plate somehow. Preferable not mark it so I can't sell it in the future.
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elf

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Re: how can I find the center of a lens (horizontal and vertical)? for panos..
« Reply #4 on: September 26, 2010, 04:53:02 am »

Gaffer's tape would probably be the best option for not leaving a mark.  Fingernail polish may be a more durable way to mark it.

For my setup, I did the following:
  • Attached camera and lens to L plate.
  • Clamped the L plate to a table.
  • Used the engineer square to verify the face of the lens was perpendicular to the table.
  • Verified the face of the lens was perpendicular to the vertical leg of the L plate (You may need to verify the L plate is exactly 90 degrees as well).
  • Measured from the top center of the lens to the table.
  • Measured the thickness of the lens.
  • Calculated the center distance.
  • Marked this distance on the vertical leg.
  • Repeated the measuring steps from the bottom of the vertical leg and applied this to the base leg.


For my setup, I adjusted the camera position on the base arm so changing from landscape to portrait mode didn't change the position of the lens entrance pupil.  I don't know if your L bracket is capable of doing this, but it might just need a spacer block to make each position equal.
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Dick Roadnight

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Re: how can I find the center of a lens (horizontal and vertical)? for panos..
« Reply #5 on: September 26, 2010, 06:04:48 am »

You want the optical axis of the lens at the entrance pupil...

I would have thought that you would have been better off doing some panos, with near and far subjects, seeing or measuring the errors on the images and making adjustments.
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Hasselblad H4, Sinar P3 monorail view camera, Schneider Apo-digitar lenses

elf

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Re: how can I find the center of a lens (horizontal and vertical)? for panos..
« Reply #6 on: September 26, 2010, 04:09:05 pm »

You want the optical axis of the lens at the entrance pupil...

I would have thought that you would have been better off doing some panos, with near and far subjects, seeing or measuring the errors on the images and making adjustments.

It's quite a bit faster to dial in the entrance pupil location if you have the lens centered on the rotation axes first.
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AJSJones

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Since L-brackets are (usually) unique to a camera model, marking the optical axes on one that doesn't have them, could be viewed as a selling point!
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RFPhotography

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It's quite a bit faster to dial in the entrance pupil location if you have the lens centered on the rotation axes first.

But a standard L-bracket won't help in that regard.  Finding the horizontal and vertical centres (rotation point) isn't what you want for panos.  Well, it is, but it's not all you want.  You need the forward and backward movements of a VR pano head to find the optical centre.  If Aristoc doesn't have a VR pano head then he's still prone to parallax errors. 
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Aristoc

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Hi
I have the RRS ultimate omni package equipment which will do just about anything. however I had to buy the L plate for my camera from Kirk for my camera with the battery grip. Kirk bracket does not have the centre of the lens marked on the bracket. So i have to do this manualy. I am just trying to eliminate as many errors as possilbe.

I will try some panos with what I have so far and then see my results.

Thank you

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