Specifications

Light energy from any observatory red light will be a serious source of error for this photometer.

Tungsten lamps are a rich source of IR in the spectral band that this instrument is most sensitive

to. Even interior observatory surfaces which are dimly illuminated by the red light and near the

front of the telescope will affect the reading substantially. What might appear as a good black

paint in the visible spectrum may appear gloss white in the J and H bands. Before taking any

readings with the SSP-4, it is recommended that the user experiment with the illumination in the

observatory to gauge the effect it has on the count. Tungsten lamps with a thick heat absorbing

filter or florescent lamps with a red filter are suggested for use as night-lights around the

telescope. Red LEDS would also be a good choice since they have no IR emissions. One other

note based on experience, the use of black vinyl electrical tape to provide a light seal is an

exercise in futility. Aluminum foil duct tape is best for sealing any light leaks.

3.2 USING THE PHOTOMETER

With the mirror down, site the star or sky region in the center of the reticule. After confirming

that the telescope is tracking properly, carefully flip the mirror up and record the readings.

To take a star or sky brightness measurement, three consecutive readings of 10 seconds

integration time (INTG set for 10) each are normally taken. Always ignore the first reading since

the mirror can never be flipped up exactly at the beginning of a new 10-second cycle. After

seeing the first count displayed, record the next three.

After the reading sequence is completed, return the mirror to the viewing position and confirm

that the star is still centered properly in the reticule. Normally, if the star is within a circle of 0.35

radius of the scribed ring center, the detector has collected more than 99% of the star’s light. This

rule of thumb does depend on seeing quality.

At this point, the user has successfully completed making a reading and is referred to other

sources of information about stellar photometry.

3.3 THE 2-BUTTON INTERFACE

Integration time, voltage-to-frequency gain and detector operating temperature can be selected

using the 2-button control. In order to get to the menu of selections, hold down the MODE key

until “STOP” is displayed. If the photometer is in the process of taking a count with a long

integration time, it will be necessary to hold down the key until the end of the process. “STOP” is

displayed for 1 second and replaced by a “Y N” over the SELECT and MODE buttons. If no

action is taken for 5 seconds or the MODE key is pressed, the program is returned to the normal

operating loop and a new count is initiated. If the SELECT key is pressed, the program is put into

the menu routine. See figure 3-2 for a guide to navigate the flow chart of all possible selections.