Scope Calculator 2

Scope Calculator 2 is tool for storing, comparing, and determining the characteristics of up to 7 eyepieces when used with a given telescope, for example, magnification and exit pupil. It is designed to be a simple and flexible alternative to doing these calculations on a traditional spreadsheet program such as Excel. All the parameters the application uses can be changed by the user, and if desired stored for later use.

Installation

Place the application in the folder of your choice. The Macintosh version of Scope Calculator 2 is designed to work on any computer running OS X, the Mac Classic version on any computer running Mac OS 9, and the Windows version any computer running Windows 95 or better.

Quick Start

Launch Scope Calculator 2. The application opens to the main Calculator panel that contains a row at the top for the telescope parameters, and then seven rows for the eyepiece parameters. By default, these are all empty. If you want to quickly see how the application works, click on the Settings button to switch over to a second panel. You'll see a button labelled Defaults; click on this button and some values based on my telescope and eyepiece will be loaded. Before you go back to the Calculator panel, notice three values have been filled in at the top of this panel. The first is a maximum magnification estimate, which is for historical reasons usually quoted as some number per inch of aperture. A common value used for this is 30, but with exceptional telescopes or on nights of very good seeing you can sometimes get away with a much higher value. The second value is the magnification of a Barlow lens, and the third is the value of a reducer-corrector lens.

Now go back to the Calculator panel. You'll see three buttons running along the middle of the window, labelled Normal, Barlow, and RC. Each time you click on these, the values in some of the boxes will change. This is Scope Calculator working out the various parameters based on the characteristics of the telescope alone (the Normal button) and then with either a Barlow lens (the Barlow button) or a reducer-corrector lens (the RC button). You'll notice that as well as working out magnifications, fields of view, and exit pupils, it also colours the backgrounds to the magnification boxes, either green or orange. The box is green for values below or equal to the estimated maximum magnification the telescope will deliver, and the box is orange when this value is exceed. Put simply, if the magnification for a given eyepiece appears in an orange box, it's probably too high for your telescope. 

Adding you own data

When you're done playing with my telescope and eyepieces, you can enter your own. Go back to the Settings panel and press the Clear button. Now go back to Calculator panel. Move the mouse over the boxes and buttons and tool tips will appear (Mac OS X and Windows versions; Mac Classic users will need to turn on balloon help).

In the top row are boxes for the telescope parameters: the telescope name, its focal length, its aperture, its f/Number (or speed), and the maximum magnification it will allow. You only need to enter the Aperture and Focal length. Scope Calculator will work out the f/Number and Maximum magnification. You only need to type in the telescope name if you want.

The seven eyepiece rows are also labelled for eight different parameters. Only two need to be filled in for Scope Calculator to work, focal length in millimetres (FL mm) and apparent field of view in degrees (AFOV). The eyepiece name, field stop, and eye relief can be filled in if required, but do not need to be. The final three parameters, magnification, true field of view in minutes of arc (TFOV), and exit pupil are worked out by Scope Calculator.

Now click on the Normal button. Scope Calculator calculates the f/Number and maximum magnification of the telescope and then the magnification, TFOV, and exit pupil of the eyepieces when used with that telescope. Clicking on the Barlow and RC button does the same thing but using the appropriate modifications for increased and decreased effective focal length.

Saving your data

When you're done adding your data, you can save it. Go to the Settings panel. Press the Save button. Your data will be saved to a file in the same folder as Scope Calculator called data.txt. This is a plain text file and you can go ahead and open it in TextEdit or Notepad if you want to. You'll also see the data that was exported in the field at the bottom of the Settings panel.

Unless you use the Save button again, any subsequent changes will be lost when your quit. If you press on the Clear button, all the fields will be emptied, but the save file will be left alone. You can either enter some new data, or reload from the save file. To reload your saved data, press on the Reload button; you will be prompted to locate the data.txt button, and then Scope Calculator will load the saved data.

You can create as many of these save files as you want. Go to the Scope Calculator folder and locate the data.txt file. Duplicate it, and then rename it to something else (for example LX90.txt). When you click on the Reload button, open this file instead. You can thereby easily create different setting files for all your telescopes.

Provided you leave the data.txt file in the Scope Calculator folder, when you restart Scope Calculator, it reads the save file and will load these settings automatically. So it's best to leave this file where it is to act as your "default" settings.

Development

Scope Calculator 2 is a reworking of Scope Calculator, a HyperCard stack and application designed for the Mac OS.

2.1 -- Rewritten in RealBASIC; various modifications to layout; first Classic and Linux versions
2.0.2 -- Bug fix (Export data file handles blank Barlow and RC fields properly)
2.0.1 -- Bug fix (Calculate button erroneously reset Barlow and RC buttons)
2.0 -- Scope Calculator 2, produced using Runtime Revolution
1.4 -- Final HyperCard-based version Scope Calculator

Bugs

I'm not aware of any, but if you find some, let me know!

Neale Monks, January 2005
neale_monks@mac.com