Entrance Pupil (“Nodal Point”) Measurements

This morning I spent a couple of hours measuring the entrance pupil position (often although incorrectly called the “nodal point”) of my Nikkor AF-S 10-24 f/3.5-4.5G and AF-S 50mm f/1.4G lenses. The entrance pupil is the point around which the lens should be rotated in order to eliminate parallax when shooting multiple images that will be stitched into a panorama.

I mounted the lens on my D5000, and mounted this in portrait orientation on a tripod with a panning base. I set up a vertical rod close to the camera, and used vertical bars on a window as a far target. Both targets were checked for vertical orientation using a spirit level and the camera was levelled using the tripod levelling base. The camera was positioned so that when the targets appeared in the centre of the viewfinder, they were precisely alligned. The fore/aft position of the camera was then adjusted until no parallax was detectable in the viewfinder when panning from left to right.

Results are given as the distance from the focal plane, not from the tripod mount, so that they can be applied to any camera. For the D5000, the focal plane is 5mm behind the centre axis of the  tripod mounting hole.

Nikkor AF-S 50mm f/1.4G

Measured with near target at 2m, far target at 30m, focused at 30m.

Entrance pupil is 46mm in front of the focal plane.

Nikkor AF-S 10-24mm f/3.5-4.5G

Measured with near target at 1m, far target at 10, focused at 10m

At f=10mm – entrance pupil is 105mm in front of the focal plane.
At f=12mm – entrance pupilis 103mm in front of thefocal plane.
At f=15mm – entrance pupilis 103mm in front of thefocal plane.
At f=18mm – entrance pupilis 106mm in front of the focal plane.
At f=20mm – entrance pupilis 108mm in front of the focal plane.
At f=24mm – entrance pupilis 110mm in front of the focal plane.

Comments

I estimate the measurement error as being +/- 5mm. The entrance pupil of the prime lens approximately the same distance in front of the focal plane as the nominal focal length of the lens. The entrance pupil of the ultrawide zoom is about 90mm further in front of the focal plane than the nominal focal length.

Graveyard at St Andrew’s Church, Mooi River

I conceived this image as an entry for the Hillcrest Camera Club’s September 2010 set subject “We Rule the Night”. I wanted a spooky graveyard, with dark tones but highlights on the gravestones, and a rising moon. I chose St Andrew’s church in Mooi River, which I had visited about a year before on the way to Giant’s Castle, because it is picturesque and I thought it would be less intimidating at night than any of the large cemetaries in the Durban area.

Although envisaged as a night shot, the photo was actually taken about ten minutes before sunset. This was necessary to balance the light from the moon with the ambient light, since I wanted to retain detail on the moon rather than having it burned out to a uniform white blob; and also to get the last rays of the sun illuminating the tombstones. However it had the unfortunate consequence that the sky was quite light, which detracted from the night ambience I was seeking. I corrected this by setting the colour temperature very low to enhance the blue of the sky, and then using a red filter in the black and white conversion  to darken the blue sky.  The B&W conversion was done with DXO Film Pack using the Kodak TMax 100 emulation. I added a little grain (by setting the grain size for a medium format camera) to give some texture to the otherwise flat sky.

In order to get the moon in the shot around dawn or dusk, it had to be shot just before or after full moon. Since full moon that month was a day after the camera club meeting I shot it the day before the meeting, which was two days before full moon. One day before full moon would have been better, since then the moon would have been lower in the sky and I could have moved further back and used a longer focal length to get the same framing of the graveyard but with a larger moon.

Composition was complicated by some electricity pylons and cable that run along the hillside just behind the graveyard. I got the camera low and chose the shooting position to hide the pylons behind tombstones.

Nikkor 10-24mm f/3.5-4.5 at 24mm, f/13 and 1/60″, ISO 200.

Rock Pool at Dawn

Taken at Rocky Bay on the Natal South Coast shortly before a wave trashed my camera.

Death of a Nikon

On a dawn shoot at Rocky Bay on the Natal south coast I decided to try for a close-up of the waves breaking over the rocks. Then a bigger wave came. This is the last shot my D60 took. You can see trails at the upper left as the electronics shorted. Fortunately the lens (my Nikkor 10-24mm) survived, and insurance paid out for the D60 which allowed me to upgrade to a D5000.