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understand, but unfortunately it's rather out of date.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.
On 7 August 2016 I
discovered that my
Olympus Zuiko Digital ED 8 mm f/3.5 fisheye lens, which according to the table should
be set at 94 mm for the E-M1 Mark I, gave better results at 97.5 mm. So something is wrong in the data
below, but I'm not sure where, and whether it affects other lenses too.
E-M1 Mark II
Focal length
7-14
8mm
9-18
11-22
12-60
14-35
14-42
14-45
14-54
25mm
35mm
50mm
7 mm
118
8 mm
115
82
9 mm
113
87
10 mm
112
11 mm
85
103
12 mm
113
102
14 mm
113
84
98
66
88
88
16 mm
87
18 mm
89
93
93
64
88
81
22 mm
88
25 mm
86
64
88
70
41.2
35 mm
76
60
95
59
39
42 mm
46
45 mm
100
50 mm
58
51
54 mm
44
60 mm
50
E-M1 Mark I
Focal length
7-14
8mm
9-18
11-22
12-60
14-35
14-42
14-45
14-54
25mm
35mm
50mm
7 mm
130
8 mm
127
94
9 mm
125
99
10 mm
124
11 mm
97
115
12 mm
125
114
14 mm
125
96
110
78
100
100
16 mm
99
18 mm
101
105
105
76
100
93
22 mm
100
25 mm
98
76
100
82
53.2
35 mm
88
72
107
71
51
42 mm
58
45 mm
112
50 mm
70
63
54 mm
56
60 mm
62
E-PM2
Focal length
7-14
8mm
9-18
11-22
12-60
14-35
14-42
14-45
14-54
25mm
35mm
50mm
7 mm
123
8 mm
120
87
9 mm
118
92
10 mm
117
11 mm
90
108
12 mm
118
107
14 mm
118
89
103
71
93
93
16 mm
92
18 mm
94
98
98
69
93
86
22 mm
93
25 mm
91
69
93
75
46.2
35 mm
81
65
100
64
44
42 mm
51
45 mm
105
50 mm
63
56
54 mm
49
60 mm
55
E-PM1
Focal length
7-14
8mm
9-18
11-22
12-60
14-35
14-42
14-45
14-54
25mm
35mm
50mm
7 mm
124
8 mm
121
88
9 mm
119
93
10 mm
118
11 mm
91
109
12 mm
119
108
14 mm
119
90
104
72
94
94
16 mm
93
18 mm
95
99
99
70
94
87
22 mm
94
25 mm
92
70
94
76
47.2
35 mm
82
66
101
65
45
42 mm
52
45 mm
106
50 mm
64
57
54 mm
50
60 mm
56
Camera positioning
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
rotator:
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.
Older stuff
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.
Horizontal centring
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:
Focal length
7-14
8mm
9-18
11-22
12-60
14-35
14-42
14-45
14-54
25mm
35mm
50mm
7 mm
-22
8 mm
-19
14
9 mm
-17
9
10 mm
-16
11 mm
11
-7
12 mm
-17
-6
14 mm
-17
12
-2
30
8
8
16 mm
9
18 mm
7
3
3
32
8
15
22 mm
8
25 mm
10
32
8
26
54.8
35 mm
20
36
1
37
57
42 mm
50
45 mm
-4
50 mm
38
45
54 mm
52
60 mm
46
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.
