Setting the NPP/LPP of the lens with Laser

 

Object

1) Pre-requisite

The vertical arm of the panorama head needs to be accurately positionned. Its adequate location depends on the camera that is used. Defining one way to very quickly and accurately adjust and set the vertical arm (e.g. the vertical rail of the [NN5+R-D16]) of a spherical panohead was demonstrated in this article (Experiment #1).

Many other different methods for the same purpose of lower arm adjustment, including this one can be googled but most of them if not all require to shot photographs and subsequent processing on a computer. Simply using the camera viewfinder to aim at the Nadir (e.g. the hex screw head of the NN5) cannot be precise due to misalignment of the viewfinder/camera mirror w.r.t. the sensor.

2) (Experiment #2)

Defining a way to align a Laser Pointer (or, alternatively, a laser level) along the Lower Horizontal Rail of the NN5 in order to make it ready in a few seconds for the next step: no photo is required to be shot by the camera...

3)(Experiment #3)

Showing how to promptly set the (Camera + lens) combination at the correct NPP or LPP setting along the upper horizontal arm of the NN. The camera shall be switched on in the live view mode.

A substutute to the live view mode can be used but it would be less practical and accurate.

The means

(click on pict to enlarge)

The short laser yellow pointer shown here is actually a toy and a very cheap one as a matter of fact. The LASER beam of light happens to be oblique wrt the longitidudinal axis of the yellow body: the angle is about 5 degrees. I had to take care of this and one can notice on the photo the correction done by the grey PVC support : the yellow cylindrical body is counter-slanted (about 5 degrees) to get the laser beam precisely vertical.

One needs a target at which the Laser pointer shall be aimed: the center of the plastic circle is engraved on the material e.g. (a cross). While this is not mandatory here, we shall use a lens mount cap that is fitted with a paper pin right punched through it at its center as it was used previously for another related purpose. In addition, optionally but nice to have: a tiny round patch of aluminum foil tape is stuck on top of the flat end of the plastic head of the Pin. The aluminium surface is polished to be highly reflective (i.e. mimicking a mirror surface).

An alternative to the camera/lens mount cap could be the front cap of the lens itself. But then the center of this circular cover must be clearly visible (e.g. engraved on it). As a nice option, this center spot could be to also marked with a polished aluminum tiny circular patch i.e. a small piece of tape: see photograph:

Test specimen

Similar to the one shown on the Nodal Ninja site front page (annimation). A (NN5+R-D16) head, a camera and a lens are needed. I have used a Canon EOS 5D MarkII and the Tokina 10-17 mm, but any other combo could be used as well.

Performing experiment #2: Placing the Laser Pointer

With the camera mounted on the Upper Horizontal Arm in the correct direction, rotate this Arm so that the camera is aiming at the Nadir (i.e. toward the hex screw on top of the R-D16 -or 8- rotator). Put the Laser Pointer between the rails of the Lower Horizontal Arm and move it until the light of the Laser hits back the top of the Pointer where it came from. The beam is reflected on the camera mount cover, on the tiny mirrow at the bull's eye. The light is reflected back on the Laser pointer head (see the preceeding) where a white washer acts as a screen, as it can be viewed on the following movie looking down the laser pointer:

When the Laser beam hits the red plastic head of the paper pin, the target starts to glow in red. When the laser beam hits the target's Bull Eye (center of the head of the paper pin), the tiny mirror stops the beam and the pin's head stops glowing. This can be observed on the following movie looking up at the target:

The Laser pointer is now in place and ready for the next experiment (#3). Note: this preparation had to be done only once: Ihave managed to have this final position repeatable without having to redo the experiment:-)

Performing experiment #3: Adjusting the LPP/NPP

For instance, let's set the entrance pupil for a "six shots around" panorama on the 5D Mark II with the Tokina 10-17 mm @ 15 mm.This is quite a favorite case on my part..

The horizontal arm is raised and locked at 30 deg. from vertical because the angle between two consecutive shoots for the panorama is 60 degrees (360/6 = 2 x 30 deg.). The camera is subsequently and initially placed at the top end of the rail and is then gently pushed to descend along the rail until the laser beam shines at its brighest on the LCD screen (in camera liveview mode). Adjusting and refining the position if necessary and then lock the knob.

A movie shows this more clearly than words. The correct position has been slightlty over-passed and corrected by going back a bit at the end of the animation:

A variant: With a Laser Level

I had reported an experiment performed with an early prototype of the L-bracket-support. An improved L-bracket design allows a better or easier adjustment of the laser position and direction:

Exactly the same process and workflow as above (with a laser pointer) can be used with the Laser level. I have found this alternative method to be slightly less sensitive and consequently it is easier to set up. The measurement result doesn't differ though while the Laser pointer should theoretically be theoretically more accurat because of the slimmer beam of LASER light..

Michel Thoby

3 March 2010