View Full Version : Using zoom lenses
05-01-2008, 03:09 AM
While I'm waiting for my NN5 to be delivered I was wondering if anyone can tell if I need to find the entrance pupil point for each "focal length" on a zoom lens or is there just one for the entire range?
05-01-2008, 04:25 AM
this table may be of help.
from experience, there is no simple rule for the position of entrance pupil.
05-01-2008, 08:03 PM
Yes, you should calibrate at each focal length you expect to use (you can "guestimate" between as well). I have a 24-105 and did it for 24, 35, 50 & 70. For my 12-24 I did 12, 18 & 24. And yes, you should do it for each lens. 24 on the one is not the same as the other.
I found John Houghton's tutorial and technique worked very well. I've experienced no problem with the calibrations I did following this method: http://www.johnhpanos.com/epcalib.htm
01-07-2010, 05:49 AM
The answer to your question is: it all depends on what you are shooting.
It is a good exercise to experiment and find the NPP (No Parallax Point) for each combination of lens and focal length you're working with - however - at times you may not need it.
If your composition does not include any object in the near field (a pretty view, a mountain range, a cityscape, ...), then do not worry too much about setting your rig for optimal NPP.
If your composition includes an object in the near field (a tree, a balustrade, ...) then parallax errors will show up when you stitch your images together. You will need to set your rig for optimal NPP.
I hope this helps,
I agree with Philippe that if the objects in the image are not near the camera then the position of the Nodal Point (no paralax point, entrance pupil) is not critical.
You could determine the Nodal Point at the ends of the zoom range and at the centre to see if the position can be interpolated for the other settings.
If the zoom range is nt large (e.g. Sigma 10-10mm zoom) then interpolation will give a satisfactory result.
Determining the Nodal Point is easier the wider the angle of view and presumably you will always use the widest setting to get the minimum number of required images.
You may find this page helpful:
Best regards, Hugh
01-08-2010, 08:55 PM
i agree with the arguments. But i prefer to work out every single NNP for each zoom setting of a lens. Once you are on the way to work it out, it does not take so much more time to work out all of them. Then in field, you are free to use the zoom and the NNP setting which is fitting the best for the situation. It is only once you have to do this.
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