Set Values

Use this calculator to work out the true/actual field of view when using a telescope eyepiece.

All telescope eyepieces have an apparent field of view, which is normally something like 50^o or 60^o. This information is normally supplied by the eyepiece manufacturer. The true/actual field of view is much smaller than this, and will be more like 0.5^o to 2^o. This is the area of the sky you will see when using a particular eyepiece in a particular telescope.

The moon is about 0.5^o, so if the field of view is also 0.5^o, the moon will completely fill the telescope.

Once you have entered values into the following form, click the Calculate True/Actual Field of View button.

Download Source Files

The field of view calculator is written in PHP and is available as a free download.

Click here to download the free open source field of view calculator

JDT