Field-of View

When you click the FOV Icon, you open a dialog box that allows you to display or print customized eyepiece (FOV) Field-of-View Maps that match the view through your own telescope and eyepieces.

This feature has been designed specifically for telescope use, and will add a whole new dimension to your lunar observing program. You now have the capability of creating Field-of-View (FOV) Maps that will closely match the view through your telescope eyepieces.

This capability makes identifying lunar features easier than ever. When used in combination with the phase display, zenith angle, and correct map orientation, you have a powerful reference tool for direct lunar observation.

In order to calibrate the FOV Tool (shown below), you will have to enter your Telescope Focal Length(s), Eyepiece Focal Length(s), and the Apparent FOV of your eyepiece(s). If you are not using a Barlow Lens, you should have number 1 displayed in the Barlow Lens window.

You can enter as many telescope focal lengths and eyepieces as you wish. Each time you type a new value into a box, the Add Button is highlighted. If you click the Add Button, the entered data will be added to the FOV Manager. If you click the Apply Button, the added information will become your default data, and appear each time you open the FOV Dialog Box.

To delete unwanted data from the display, click the Delete Button. Use the < and > buttons to scroll through your telescope or eyepiece list. If you are unfamiliar with this terminology, or you do not know the FOV of your eyepieces, you can click the Info button to access some useful eyepiece FOV data.

In the following example, we will assume you are using an 8” f/10 Schmidt-Cassagrain (SCT). If you are using a star diagonal you should choose a North-Up Reversed Map. The telescope has a focal length of 2032mm, and we will begin with a 26mm Plossl eyepiece to observe the entire lunar disk. Like most Plossls, the eyepiece has an Apparent FOV of about 50 degrees.

When you enter the data in the FOV Dialog Box, and click the Apply Button, the software, (as shown below) calculates the magnification and True FOV, and enters it in the lower window. At the same time, the moon is redrawn to the correct scale, within the eyepiece field.

Once you are ready to increase your magnification, use the Centering Tool to center the same feature on the map display that you centered in your telescope field. In this example, we clicked on the crater, Longomontanus.

Now you are ready to add more magnification. Let us assume that you choose a 10mm Plossl and a 2X Barlow Lens. The Apparent FOV is 50 degrees. As you can see from the Field-of-View Dialog Box, the new magnification is now 406X, and the displayed map will match the view through your eyepiece. The phase mask was changed from opaque to semi-transparent, to allow the features on the night side of the terminator to become visible.

IMPORTANT: Never use the Zoom Buttons on the Tool Bar if you are using the FOV Dialog Box. Using the Zoom Buttons will throw the calculations off. The only correct way to increase or decrease the image scale is by entering shorter, or longer focal length eyepiece values into the FOV Dialog Box, or by entering a Barlow factor greater than 1.