**NAS Calculator Page**

*Revised 05/04/2003*

Need to know when is the best time to look at an object? That time is of course when the object crosses the meridian and is highest. This calculator allows the user to input any date and the Right Ascension of the object of interest. It then calculates and displays the Greenwich Sidereal Time at midnight GMT, the Hour Angle, and Transit Time across the meridian of the object.

**Telescope Parameter
Calculator**

This calculator allows the user to input a telescope's aperture (diameter), the focal length, a barlow power, and an ocular in units of inches or millimeters. It then calculates the telescope's effective focal ratio and length, the minimum guiding power required for photography, telephoto power over the standard 50mm lens, field of view using a 35mm camera, telescope resolution, light grasp over the naked-eye, limiting visual magnitude, minimum and maximum useful power, plus magnifications given by various oculars plus one user defined one.

**Telescope Dew Heating
Calculator #1**

Need to know what ohmic value resistor to use? This calculator allows the user to input the voltage of the source, the power of the resistor, and how many will be needed to make the loop. The calculator computes the exact resistance required, the voltage drop across each resistor, the loop amperage (current flow through the loop), and the total loop power. Use the Calculated Resistance to know what resistor to buy and always choose the next higher ohmic size. Generally a Total Loop Power of 2 to 3 watts is enough heat to keep your optics clear. After you have decided on the make up of the loop, use the next calculator to figure out the exact information on your loop.

**Telescope Dew Heating
Calculator #2**

Now that you know the source voltage, the standard resistor size you will use, and the total number of resistors, what kind of heat and current draw can I expect? This calculator allows the user to input the voltage of the source, the resistance of the resistor that will be used, and how many will be needed to make the loop. The calculator computes the voltage drop across each resistor, the power dropped across each individual resistor (must be less than resistor's rating), the loop amperage (current flow through the loop), and finally the total loop power. Generally a Total Loop Power of 2 to 3 watts is enough heat to keep your optics clear.

**Exposure Value (EV)
Photography Calculator**

Need to calculate what the exposure time should be for your optical system for a specific subject? Just input from our supplied auxillary subject tables the Exposure Value at ISO for the subject, the Film Speed (ISO) of the film to be used, and the effective Focal Ratio of the optical system that will be employed and then click "Compute". Computed results give the new EV index at the new ISO, the exposure time in fractions of a second, or decimal seconds, or decimal minutes.

*--- GLH
*

Return to NAS Home / Revised 05/04/2003