# Nodal Point on non extending Zoom Lenses



## 1982chris911 (Sep 29, 2011)

A short question about the Nodal Point of non extending zooms:

For (non-extending) zoom lenses like the Canon 17-40mm f4.0 L or 70-200mm f2.8 IS II L do you know if the nodal point shifts when zooming, or is that dependable from each lens's construction and cannot be generalized.

Just asking cause I don't see any shift on the 70-200mm right now, but maybe I was not precise enough yet when testing on the nodal rail. 

Thanks for your answers


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## willhuff.net (Sep 29, 2011)

I'm pretty sure it shifts on my 17-35L


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## Edwin Herdman (Sep 30, 2011)

Yes, the nodal point shifts all the time; the nodal point shifts when changing aperture, too!

Thankfully, you don't use the nodal point as a "no parallax point" for the purpose of composing panos (the words in quotes give a clue what at least some peoples' preferred terminology might be).

I'm just being picky because if you ask about the nodal point you're liable to either get junk responses or a technical explanation that is about THE nodal point but not about what you're actually asking about.

Here's what you're looking for:

http://wiki.panotools.org/No-parallax_point

See also this:
http://wiki.panotools.org/NPP_adapters

It's unfortunately somewhat technical, but this may help (by the author of PanoTools IIRC):

http://www.janrik.net/PanoPostings/NoParallaxPoint/TheoryOfTheNoParallaxPoint.pdf

The bottom line is that you can get by with just rotating the camera. Just find the point on your camera where you can rotate it and not introduce parallax with some test shots.

Also, I have to confess ignorance so far - I still haven't gotten whether your selected aperture actually does effect the no parallax point's location, though from what I've read so far it seems that it doesn't.


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## dougkerr (Sep 30, 2011)

Hi,



1982chris911 said:


> A short question about the Nodal Point of non extending zooms:
> 
> For (non-extending) zoom lenses like the Canon 17-40mm f4.0 L or 70-200mm f2.8 IS II L do you know if the nodal point shifts when zooming, or is that dependable from each lens's construction and cannot be generalized.


If your interest is in multi-frame panoramic photography, you have no reason to be concerned with either of the two _nodal points_ of a lens. They are not relevant to that issue.

You do need to be concerned with the often-called "no-parallax point", which falls at the center of the _entrance pupil_ of the lens.

Note that you can look into the lens from the front and locate this. It is where the aperture diaphragm *looks to you as if it is* looking from outside the lens in the front.

I just took a quick peek into my Canon EF 70-200mm f/2.8L IS. It does not look as if the entrance pupil moves much (if at all) when changing the focal length.

Best regards,

Doug


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## 1982chris911 (Sep 30, 2011)

Well the reason why I refer to this as the Nodal Point is actually cause I own this Nodal Point Rail, which was just made for this purpose to adjust the lens for Panoramic stitching:

See here: http://acratech.net/product.php?productid=62


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## dougkerr (Oct 1, 2011)

1982chris911 said:


> Well the reason why I refer to this as the Nodal Point is actually cause I own this Nodal Point Rail, which was just made for this purpose to adjust the lens for Panoramic stitching:
> 
> See here: http://acratech.net/product.php?productid=62


I understand.

Best regards,

Doug


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## dougkerr (Oct 1, 2011)

Hi, Edwin,



Edwin Herdman said:


> . . .the nodal point shifts when changing aperture, too!



I have never heard of either of the two _nodal points_ of the lens, nor the center of the _entrance pupil_ (which corresponds to the "no-parallax point"), shifting with change in aperture.

Any of those three can, of course, change with change in focal length (for a zoom lens), or maybe even with focus position (for some focusing systems).

Best regards,

Doug


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