**Exposure**

This section is for performing Exposure calculations.

For the **Exposure
Ratio** calculation enter any three inputs Aperture Diameters D1 and or D2,
and or Exposure Time 1 and/or 2. Which ever of the 4 is missing will be
calculated. Press “Calculate” to compute or “Clear” to erase and try
again.

For the lower **F
Exposure Ratio** calculation by selecting the check box value the user can
select pull down combo entry of f/ ratio or hand entry to a text box.
The exposure ration is a factor ratio on f/1 at 1 sec exposure. Press
“Calculate” to compute or “Clear” to erase and try again.

For the upper **F
Exposure Ratios** calculation by selecting the check box value the user can
select pull down combo entry of f/ ratio or hand entry to a text box for f/
ratio for input 1 or 2. Next enter the one of the exposure times and ISO
settings for input 1 or 2 and the calculation for the other exposure and ISO
values will be calculated. Press “Calculate” to compute or “Clear” to
erase and try again.

For the **Exposure
and Star Trails** calculation enter the exposure time and f/ ratio and
selecting the Min/Sec will be used to determine if answer for Trail Length is in
minutes or seconds. Also select the detector (CCD, Camera etc.) ASA setting and
the Object type (thus the brightness factor) and the Max Time for No Star Trail
and Exposure time will be calculated. Press “Calculate” to compute or
“Clear” to erase and try again.

For the **Brightness** calculation
you may enter the Magnitude and area in square arc-sec and press calculate the
brightness. Entering the Brightness with the magnitude box empty, will calculate
the Magnitude from brightness. Press “Calculate” to compute or “Clear”
to erase and try again.