Quick question about lens feet...

[sk66]

The foot on a lens is placed for balance right? It wouldn't also be at the focal center would it? Maybe by chance, but not design?

[xxpinballxx]

foot? Do you mean the little flat spot on bigger lenses? If thats what you are talking about that is the collar to mount on the tripod due to the weight it keeps the strain off of the mount.
If you are talking about something else then i have never seen feet on a lens.....

[Murtasma]

Are you talking about the nodal point?

[sk66]

Yes, the little flat spot on bigger lenses...

I know "what it's for", but I was kind of hoping it is *also* placed at the focal center...for panoramic shots.

It occurred to me that the foot is often much larger than needs to be...and that a matching arca plate is also much longer (in comparison to most arca heads)....That made me "hope" that it is also a "feature" which allows the lens to be mounted at it's focal center...

I don't often (read as "never have yet") taken a multi-shot panorama, but I might like to....

[sk66]

Originally Posted by Murtasma

Are you talking about the nodal point?

YEAH, that thing!

[Murtasma]

My understanding is the nodal point changes depending on what focal length you are shooting at so the foot could very well be at the nodal point at one very specific focal length but not at any others.

http://www.photoshop-tutorials-plus....noramas-3.html
http://archive.bigben.id.au/tutorial...d/history.html

These are both good sources to find the nodal point of the lens. The 2nd link I think is a more comprehensive site.

[sk66]

Yeah, it would move with zooming, that's why I was correlating it to a long foot..the long foot allows the lens mounting point to also move..

BTW...after a little quick research I realize that "focal center" was the wrong term, and that "Nodal point" may also be the wrong term in the strictest sense...I believe the most correct term is "optical center"...but I don't really care.....as long as we are talking about the same thing...

[Murtasma]

Originally Posted by sk66

Yeah, it would move with zooming, that's why I was correlating it to a long foot..the long foot allows the lens mounting point to also move..

BTW...after a little quick research I realize that "focal center" was the wrong term, and that "Nodal point" may also be the wrong term in the strictest sense...I believe the most correct term is "optical center"...but I don't really care.....as long as we are talking about the same thing...

Yep if you attach on of those plates you could certainly adjust it so it was at the nodal point of the focal length you are shooting at for stitching.

[xxpinballxx]

the only thing is that collar is adjustable depending on the amount of barrel to put it on so you may be off or right on depending on where its tightened down to.....
I never thought about it being helpful in panaramic? good question....

[inkista]

I actually wouldn't count on the tripod ring area being the no-parallax point of the lens. It's never that simple, damnit.

The easiest way to find the no-parallax point of the lens is to pray that it's in the panotools wiki's "Entrance Pupil Database". If it isn't, though, then you have to do tests.

The easiest way is to set up two vertical markers of some kind that line up (say, a lamp post and a door edge, one behind the other from a given viewpoint. Then, rotate the lens a little around what you think is the no-parallax point, and if the two markers stay lined up, then you've found it. If they don't, then you need to adjust the rotational point of the lens and try again.

An adjustable panohead (not to be confused with a panning head) is indispensible for this kind of thing. I highly recommend the NodalNinja 3, but I've only used it with a fisheye lens, not a telephoto. You might have to get the 5 [longer rails] for a larger camera/lens set up.

Now, may I ask why you need to find the no-parallax point of a larger telephoto lens? You're unlikely to be dealing with a lot of parallax error in panos if you're shooting, say, high-resolution landscapes with everything far away from you. It's only if you want to do the gigapixel thing indoors or with objects in the near foreground that you need to be that precise. For the outdoors stuff you could probably even get away with handheld if you wanted.