The grid

Method for a precise location of the entrance pupil on a DSLR(*) camera

Alain Hamblenne / OUTLINE Graphic Designers - www.outline.be (september 2004)
English translation: Mickael Therer - www.360days.com

he technical progress in the domain of panoramic

photography along with the expansion of broadband
Internet connections have allowed for a considerable
rise in the quality of panoramas and their full screen
presentation.
The flipside of this breakthrough
is that any imperfection becomes
much more noticeable and
demands tedious retouching
prior to publication.
In order to near perfection,
starting from the shooting time,
it is crucial to match the entrance
pupil of the lens (also inaccurately referred to as nodal
point ) with the 2 axis of the
spherical panorama head (leftright rotation and up-down tilt).
This ensures a perfect stitch of
the pictures by getting rid of
parallax errors for good.

september 2004 - Alain Hamblenne /OUTLINE Graphic Designers - www.outline.be

How to precisely locate

the entrance pupil ?
For the beginner panoramist, this
quest often resembles that of the
Holy Grail everybody is talking
about it but its precise location
remains hard to find.
This is my method to locate the entrance
pupil with precision ... a simple grid !

(*) If you use a non reflex camera, it is definitely

possible to follow the method as described.
Check your step by step results in your favourite
image editor (Adobe Photoshop, ...).

Different methods, some more or less complicated, allow

achieving decent results for most cylindrical panoramas.
The difficulty increases, as multiple rows of images need to
be stitched in order to achieve cubic or spherical panoramas.
Often one believes to have spotted the darn entrance pupil,
then as it happens that they shoot a pano with a nearby
foreground, problems are revealed and perfect stitching
becomes impossible.
Here is the method I use. It will help you locate the entrance
pupil on any reflex digital camera, whatever lens or add-ons
it is mounted with.
Simple and error free, it also allows fine-tuning of settings by
eliminating slight horizontal and vertical shifts.

Page 1

The grid - Method for a precise location of the entrance pupil on a DSLR camera
The required hardware

The installation

A digital reflex camera mounted

on a tripod with a spherical
panoramic head.
For this demonstration, the following
hardware was used :
- A Minolta Dmage 7Hi (28-200)
- A Manfrotto (Bogen in the US) tripod
- A Manfrotto QTVR Kit (head)
- A Kaidan QuickPan spherical arm

Run the rope into the top meshes of the grid and tie the ends to the walls (or
posts) so that the center of the grid hangs approximately at eye level.
The weight of the grid strengthens the setup and allows near vertical selfstabilisation if there is no wind ! ;-)

a stiff grid as fine as possible.

Here a stand for kitchen utensils
is used. ;-)
a piece of rope to suspend the grid
a courtyard with 2 nearby walls (or
posts) to tie the rope onto
no wind (grid stability) !
a little patience !
You now have all the ingredients, lets
move on to the recipe !

september 2004 - Alain Hamblenne /OUTLINE Graphic Designers - www.outline.be

Fasten the camera on the tripod with the spherical bracket, and place the whole
setup as close as possible to the grid, leaving just enough free space to allow
rotating the camera without hitting the grid.

The hardware is set up in front of the grid.

Tip ! If you wish to centre the grid with the lens (it will look nicer !) all you need to
do is slide it on the rope to bring its centre in front of the lens. Then level the tripod height to match its centre.
Remark : it is not necessary that the grid be parallel to the camera or the ground.
But as soon they are both installed, the grid and tripod should not move at all
during fine-tuning.

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The grid - Method for a precise location of the entrance pupil on a DSLR camera
Step 1. Basic adjustment

Step 2. Fine-tuning during horizontal rotation

For a good adjustment, the horizontal

rotation must be centred on a vertical
virtual axis running through the
entrance pupil.
Start by positioning your camera so
that the centre of the lens (as seen
from the front) is as precisely as
possible at the vertical of the rotating
axis of the spherical bracket.
This basic preliminary adjustment can
be measured by eyesight, or better
with a plumb line.

The camera being perfectly levelled on the horizon

(inclination at 0 see spirit-level on the opposite picture),
sweep the camera from left to right and observe carefully
in the viewfinder (or on the LCD screen), the movement of
the background behind the grid. The grid is here the
nearest foreground.
Check the Spirit level !

330

30

Here, the camera is not well positioned. The rotation axis is just 10 mm behind the entrance
pupil. Note the shifts between the background and the verticals of the grid (window frame, flower
jars, table-tennis table, etc.).

september 2004 - Alain Hamblenne /OUTLINE Graphic Designers - www.outline.be

The centre of the lens and the rotating axis are

on a same vertical line.

Tip ! Level your camera perfectly at

-90 (towards nadir) and match the
centre of the viewfinder with the screw
on the central axis of the spherical
bracket. This is not always possible. In
my situation, this screw is hidden by
the rulers and by parts of the quickrelease Manfrotto attachment plate.

Adjust the camera positioning on the bracket by moving it to the front or to the
back and/or left or right (as in step 1) until no more shifting occurs between the
background and the grid during a horizontal rotation.

Warning ! If you are using a camera with a

zoom lens, lock the focal length at which
you will be working (e.g. 28mm) as well as
the focus point. Modifications to any of
these two during the adjustments will alter
the location of the entrance pupil and all
settings would be lost.
The same views after fine-tuning the horizontal rotation. No more misalignments between the
background and the grid in the foreground.

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The grid - Method for a precise location of the entrance pupil on a DSLR camera
Step 3. Basic adjustment

Step 4. Fine-tuning during vertical tilting

For a good adjustment the camera

must also tilt on a virtual horizontal
axis running through the entrance
pupil of the lens.

With the fine-tuning of the horizontal rotation done (see steps 1 and 2),
chances are high that the overall positioning of the camera is correct.

Position your camera so that the

centre of the lens (as seen from the
front) is precisely at the same height
than that of the tilting axis of the
spherical bracket.

To verify or fine-tune the settings, you can proceed the same way this time tilting the camera up and down and observing carefully in the viewfinder (or on
the LCD screen), the movement of the background behind the grid.

This basic preliminary adjustment can

be measured by eyesight, or better
with the help of a spirit level (see also
Tip ! at step 1).

The centre of the lens and the tilting axis are

on a same horizontal line.

+30

-30

september 2004 - Alain Hamblenne /OUTLINE Graphic Designers - www.outline.be

Here, the camera is misaligned. The tilting point is simply 10 mm behind the entrance pupil. Note
the subtle shifts between the background and the horizontals of the grid (window frame, water
hose, window sill, etc.).

If necessary, improve the camera positioning on the bracket by moving it to the

front or the back and/or up or down (as in step 3) until no more shifting occurs
between the background and the grid during a vertical tilt.

The same views after fine-tuning the vertical tilt. No more misalignments between the background and the grid in the foreground.
Your camera is now perfectly adjusted on the entrance pupil of the lens !

Page 4

The grid - Method for a precise location of the entrance pupil on a DSLR camera
Proof by sight
Most programmes used to stitch panoramas adapt for small glitches in camera
positioning with more or less distant subjects.
Pan = 330
Tilt =
0

Pan =
Tilt =

0
0

Pan =
Tilt =

30
0

Pan = 330
Tilt = -30

Pan =
Tilt =

0
-30

Pan =
Tilt =

30
-30

Pan = 330
Tilt = +30

Pan =
0
Tilt = +30

With a very near foreground (fence, balcony, etc.), it is another story ! It becomes
impossible to stitch images together (due to parallax errors) if the 2 axis of the
spherical bracket (horizontal rotation and vertical tilt) are not running precisely
through the entrance pupil.

Pan = 30
Tilt = +30

Different positions of the camera across nine

test shots (3 rows).

A poor setting for the entrance pupil does not allow for a good
stitching of the foreground. Artefacts and ghosts appear that can
hardly be recovered.

september 2004 - Alain Hamblenne /OUTLINE Graphic Designers - www.outline.be

Stitching in Realviz Sticher 4.0.2

Here, the position of the entrance pupil has been perfectly located for
the 2 axis (horizontal rotation and vertical tilt), the stitching process is
smooth and the result impeccable.

rue Destriveaux 10
B-4000 Lige
Belgium
Phone +32 (0)4 254 29 30
Fax +32 (0)4 254 15 13
studio@outline.be
www.outline.be

I hope you will find the grid useful and that it will help you achieve better
results with your panoramas.
If it turns out that you do improve your panoramas, I would be happy to hear
from you ! ;-)
Alain Hamblenne
studio@outline.be

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