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 Post subject: optical axis/diaphragm
PostPosted: Tue Aug 12, 2008 3:45 am 
could anyone tell me where the optical axis of the Tamron 28-80 mm lens is?
ie how far along the lens barrel is it from the camera mount?
i have tried to look through the lens optics at it but its impossible to judge;
maybe someone has disassembled it? im not too keen to try doing that myself. the reason i need to know this is that i need to find the exact pivot of it (no parallax) for a panorama robot i am making.

 Post subject:
PostPosted: Tue Aug 12, 2008 1:28 pm 
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Joined: Sat Sep 30, 2006 4:30 pm
Posts: 9886
Location: UK
Hi colagor,

May I wish you a warm welcome to the CameraLabs forums.

I think the term you need to use is "optical center", sometimes referred to as "nodal point", rather than "optical axis". As I'm sure you know, positioning the camera so that the panorama head's rotation axis passes through the optical center requires a bracket such as

If you are lucky then Tamron's technical support guys might be able to provide you with the exact distance along the barrel of your lens' optical center. Alternatively, there is a tutorial here at the Really Right Stuff site and they also provide a link to another site from which you can download this PDF document with a much more detailed guide.

Discovering the optical center will take some time but once it's done and the camera bracket is marked appropriately it should never need repeating so I guess it's worth some effort to get it right. 8)


Sony RX1R II. Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, M.Zuiko Digital ED 40-150mm f/2.8 + 1.4x T/C, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8
M.Zuiko Digital ED 75mm 1:1.8, Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.

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