View Full Version : negative nodal point?
03-28-2010, 02:29 PM
I calibrate today with Nikon 180mm f2.8 AFD and the nodal point value on upper rail go beyond the rotating knob and I got around 10mm (negative) value of upper arm. Is it true? I thought nodal point for long lens for upper arm is always positive and greater value.
03-28-2010, 10:22 PM
Sometimes nodal point can be opposite what you expected, it's pretty rare but it occurs. Perhaps mount camera in other direction on arm ? What is you configuration exactly ?
03-28-2010, 10:34 PM
Longer lenses do have this problem. Nikkor 70-200/f2.8 needs the upper arm turned forward with zoom 105 with an upper rails set of 44. With zoom 200, the NPP is positioned behind the sensor plane, upper ail set 135. I hope you do not end up on the rotator.
03-28-2010, 11:50 PM
For simple lenses, the entrance pupil (not the nodal point, BTW) is normally positioned towards the front of the lens. It's the aperture's apparent position when you look into the lens. Telephoto lenses are much more complex and the entrance pupil can be several cm behind the camera sensor. With a zoom lens, you can see the entrance pupil move forwards/backwards as you change the zoom setting.
03-29-2010, 08:43 AM
I am testing with Prime 180mm f2.8 AF -ED and the nodal point looks like in rotator joint. I still get small parallex error when I test with John's method with the camera on the other side of the arm, I mean I have to turn the arm to the front side and mount the camera.
I will try with another prime 300mm f4 AFS in coming weekend.
04-04-2010, 05:19 PM
I tested today with 300mm f4 AFS and there is still small parallex error even the lens and camera reach the other end.
Here is how it lookshttp://farm3.static.flickr.com/2800/4491645112_a705fdc5cc.jpg.
I am not sure how people set for long lens with large panorama photo.
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