exposure time curves for common integrated light sensors
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See also the do
it yourself kit incl PCB for a simple but reasonably accurate light
This is an interactive interface for generating exposure diagrams for
use with inexpensive and easily available integrated light sensors together
with familiar holographic emulsions; these diagrams are ready to use and
take all the relevant factors (like wavelength-dependent sensor and film
sensitivities) into account.
In principle, the optimal values (which may also depend on developer,
film age, etc) should be obtained by trial and error, starting from the
these data as a first approximation. However, I found these values to
be sufficiently accurate as they are, for the sensor/film combinations
I tried out. There is some considerable margin in the exposure time,
so that some tens of percents of variation are hardly noticeable in the
final hologram. Some crude estimates for tolerable margins (30%) are indicated
by the dashed lines in the figures.
beam incidence angle
Explanation of the possible settings
Most entries are for common, easily available light sensors that combine
photodiodes with integrated amplifiers, and give an output voltage that
is linear with the illumination over a wide range. Their sensitivity is
just right for the intensities typically used in holography. They thus
provide a cheap and extremely simple way to build photometers for holography
with sufficient accuracy.
See here for a more detailed
description of various monolithic light sensors, and a simple do-it-yourself
circuit based on the familiar sensors OPT101/OPT202.
I added also an entry for the wide area PIN diode UDT PIN10-AP used with
an external amplifier. This refers to my old-but-proven photometer circuit
Moreover, I also added an entry for the Thorlabs Silicon Power Meter S20MM.
Film types and wavelength:
Pretty much self-explaining. More emulsion types can easily be added
upon request. For the Slavich products the center line corresponds to
the illumination density associated with the highest diffraction index,
as listed in their data sheet (corresponding to optical density OD=2,
Reference beam incidence angle:
When the reference beam hits the film plane at an angle (typically the
Brewster angle, which is ca 56 degrees with respect to the normal), the
actual intensity per square cm on the film plane is less (by a factor
of 1/cos(alpha) = 0.55) than what a light sensor aiming straight into
the reference beam suggests. Thus we provide an option for automatically
taking this factor into account. Obviously, for holograms with perpendicular
reference beam, the zero degree incidence angle option should be chosen.
We consider the reference beam because it is stronger than the object
beam. The readings need to be modified if one has a high object intensity.
For zero incidence ref beam angle, simply add the average object beam
mV reading to the ref beam reading. For 56 degree ref beam angle, add
twice the object beam mV reading; in particular, for the usual 1:4 object/ref
beam intensity ratio, add 50% extra to the mV reading of the sensor.
Example 1 - transmission hologram (using the default
Assume you use a TSL250R at 633nm with a PFG-01 film, and when aiming
into the reference beam at Brewster angle, you get a reading of 1V. If
the object light is very weak, then the exposure time should be around
26sec. If the object intensity is, say 250mV (so you have a 1:4 ratio),
then you add twice this value to the reference beam value, which makes
1.5V. From the diagram you see that the exposure time should be around
Example 2 - Denisyuk hologram
Assume you use an OPT202 at 532nm with an Ultimate 08
plate, with a single beam setup where the reference beam hits the plate
at near right angle. Assume that when aiming into the reference beam,
you get a reading of 80mV while the object light gives 20mV. From the
diagram you see that the exposure time for 100mV total should be around
Example 3 - H2 image plane reflection copy from
Assume you use an OPT301M at 514nm with an Ultimate15
plate, with a reflection setup where the reference beam hits the plate
at the Brewster angle, and the real object image intersects the plate.
The intensity of the object light will thus be much higher as for a transmission
setup, and my rule of thumb is to find the brightest spot and aim for
a reference/object ratio of 1.5-2 at this spot. In a concrete example,
the maximal object intensity was 80mV and the reference was 170mV. So
alltogether we count 2x80+170=330mV, which yields approx 6s exposure time
according to the diagram. These are the actual data that
were used to create the ultra-bright reflection copy shown here.
I made some precise measurements and found that all detectors
I used (TSL250R, TSL251R, OPT101, OPT202, OPT301M, UDT PIN-10) gave consistent
answers within 20%. Specifically, for the sensor OPT301M and film VRP-M
developed with JD-2, I achieved an optical density of OD=2 right on the
line of the relevant plot (and OD=1 on the dashed line to the left) -
precisely as it is supposed to be !
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Vers 1.7, 10/05