This page contains details about how to adjust my panorama hardware to position the entrance
pupil of the lens in a position where it can be rotated around two axes without moving from
its position (the “no-parallax point”). The values are specific to my hardware, but the
principles aren't. It's based on a table for my Olympus cameras at http://olypedia.de/Nodalpunkte_E_System. It's in German, but easy enough to
understand, but unfortunately it's rather out of date.
The basic principle is simple: the entrance pupil of a lens is a certain distance from the
sensor. For a zoom lens it will probably change with focal length. Things are somewhat
complicated by the fact that you can't easily measure from the sensor, only from the tripod
mount, and Olympus delights in changing the position of the tripod mount (for example,
there's a difference of 12 mm between the OM-D E-M1 Mark I and the
OM-D E-M1 Mark II). The German page gives offsets from sensor to tripod mount for most Olympus cameras.
If your lens isn't listed, you can either measure the entrance pupil location
yourself—something I've found far too inaccurate—or guess that it's roughly at the middle of
the front element of the lens.
The tables below assume correct positioning of the camera (below). They're the total distance along the lens axis as shown on my positioning rail,
including the distance from sensor to entrance pupil on the one hand and sensor to tripod on
the other hand. Your mileage will vary.
To take a good panorama, you need to eliminate parallax between the individual shots. This
means that the camera must be in the same position for each shot. But which part of the
camera? If you turn it, most parts will be somewhere else.
The part that's important is where the light goes into the lens, technically called
the entrance pupil. Very
frequently people call this the nodal point,
though this is incorrect.
So where is the entrance pupil? There's a simple answer and an accurate answer. The simple
answer assumes that the entrance pupil is on the lens axis, so the only thing you need to
know is how far along the axis it is positioned.
And the accurate answer? For some lenses the position of the entrance pupil depends on the
angle of view. Not only is it not always on the lens axis, it's not even a point: it's an
area. Like most people, I put this category into the “too hard” basket.
So how do you measure the entrance pupil? There are various methods, which I won't describe
here. I simply rely on other people's measurements. There's a table of entrance pupils for
my Olympus cameras at
http://olypedia.de/Nodalpunkte_E_System. It's in German, but easy
enough to understand.
Knowing the position of the entrance pupil isn't enough. The distance is measure from the
sensor, not something that you can easily locate. Normally you screw the camera on a rail,
so the reference point is the tripod mount, which may be offset from the sensor in all three
directions. In particular, it could be offset along the optical axis. The German table
gives measurements for this as well. In my case, the tripod mount of the Olympus OM-D E-M1 is 2 mm
behind the sensor, while the mount of the Olympus E-PM2 is 5 mm in
front. These values need to be added to or subtracted from the values in the table. I'll
discuss offsets in the other two directions below.
My current hardware includes a bracket mounted on a rail, which in turn is mounted on a
The scale on the longitudinal rail shows the distance between mounting point and rotator
axis. The other two rails are lateral, and in principle one is superfluous, but the bottom
arm of the panorama bracket is too short, so this enables me to position the side of the
bracket further from the vertical rotational axis:
The important thing to note from the front view is that the lens axis intersects both the
rotational axis of the rotator and the rotational axis of the rotator at the left-hand
side. These don't need to be adjusted. Along with the adjustment along the axis, this
ensures that the entrance pupil stays in the same place regardless of rotation.
The following is from an earlier version of this page. Under some bizarre circumstances it
could be of use.
First I need to mount the cameras, an Olympus OM-D E-M1 and an
E-PM2 on my
hardware, consisting of a cheap, badly designed panorama bracket and a couple of focusing
rails to compensate for the design errors of the bracket. The camera is mounted on one of
two different “Fotomate” rails (more of that below) which in vertical orientation fits into
the mount of the upper rotator of the panorama head (the L-shaped frame on the left). These
photos show a previous camera, an Olympus E-30.
The panorama bracket comes with a useless rotator which is not adjustable in position along
the rail to which is mounted. It is wrong for anything I want to do. I haven't been able
to remove it, so I have just locked it in position so that it doesn't rotate and mounted it
on a 16 cm Fotomate rail, which in turn is screwed to a Sunwayfoto DDP-64M rotator below (not visible here, but directly below the plate with “FOTOMATE” written on
it), which does work well. The toy rotator is the cylinder round offset 8 mm on the rail.
For this particular hardware and (vertical) orientation, the camera is centred above the
rotator when the scale is set to 4.4 cm. In horizontal orientation it needs to be
readjusted to 5.8 cm:
In horizontal orientation, it's also important to ensure that the axis of the lens is at the
height of the upper rotator (or the toy vertically mounted compass attached to the clamp).
In vertical orientation this happens automatically.
The position of the camera along the upper rail depends both on the lens and on the rail I
choose. The following is an adaptation of the information at http://olypedia.de/Nodalpunkte_E_System. It reduces to readings on the scale of
the 16 cm Fotomate rail:
This rail has a distance of 108 mm from the tripod mounting hole when the scale is set on 0
and the camera is mounted at the far end of the adjustable slot. The scale is the wrong way
round, so the distance reduces as the scale indication increases. In addition, the tripod
mounting hole of the E-M1 is 2 mm behind the sensor plane, and the mounting hole of the
E-PM2 is 5 mm in front of the sensor plane so this value needs to be added. The real value
for the E-M1
is thus offset = 108 + 2 - scale, or scale = 108 - offset - 4.
The magic here is a little function that converts the individual values in the table, so
that I don't have to do it manually:
I can't set negative values (the ones marked in red), so for those values I need to use a
longer rail (26 cm), again from Fotomate:
This one is presumably meant for mounting flash units. As shown, it is set with the
mounting hole directly below the inside end of one of the slots. The scale shows 9 mm left
of the 0 point on the scale. If I mount the camera in this position, at the right end of
the left slot, and point it to the right, I can move the base of the rail as far as 121 mm
in that direction (not quite to the end of the scale), giving me a total range of 130 mm.
In this case the calculation is more straightforward: offset = 108 + 2 - scale,
or scale = offset + 2 - 9.