Astronomy Hacks

Enhance Lunar and Planetary Contrast and Detail

Choose a basic set of filters to improve the view.

Just as photographers use filters to alter the images captured by their cameras, astronomers use filters to alter the images visible in their eyepieces. A filter, by definition, can add nothing to an image; it can only take away. But, like the sculptor who creates an elephant from a block of stone by cutting away everything that doesn’t look like an elephant, an astronomer may use filters to create more detailed views of some objects by removing extraneous light to allow the subtle details of the object to show through.

Astronomical filters are available in several sizes. The most common are those that fit standard threads on 1.25” and 2” eyepieces and the visual backs of Schmidt-Cassegrain Telescopes (SCTs). Meade goes its own way, using a non-standard thread on their 1.25” and 2” eyepieces and filters, and Questar uses still a different thread. A few filters are available for 0.96” eyepieces, which are common in Japan and with some old telescopes but rare elsewhere. Filters for 1.25” eyepieces are available in by far the widest variety. The selection for 2” eyepieces is somewhat more limited, and those for SCT visual backs are even more limited.

Tip

If you use both 1.25” and 2” eyepieces, consider buying only 2” filters. Although a 2” filter cannot be attached directly to a 1.25” eyepiece, there are two common workarounds. First, many 1.25"/2” focuser adapters provide threads for mounting ...