Comet Machholz passes near M45, the Pleiades. Taken with a Canon EOS 1D Mark II DSLR camera and a 70-200mm zoom lens at 200mm of focal length at f/2.8 at ISO 800 with a 3 minute exposure with the camera and lens riding on top of a telescope on an equatorial mounting tracking the stars.

The next step up in long-exposure deep-sky astrophotography is to place a camera with a longer focal-length lens on top of a polar-aligned, equatorially-mounted telescope.

Because the scope and camera are mounted on an equatorial mount, it can track the stars with movement of only it's right ascension axis. If the mount is accurately polar aligned, it can follow the stars for longer time exposures of up to several minutes. Such a setup can yield time exposures with longer focal length lenses that reveal more detail in celestial objects. Here, the greenish-blue color of the coma of the comet can be seen, as well as some blue reflection nebulosity around the Pleiades.

The photo above was taken with an zoom lens piggybacked on top of a refractor that was on a Losmandy equatorial mount. It was shot with a Canon 1D Mark II DSLR camera at ISO 800. The photo is a 3 minute exposure taken at f/2.8 at 200mm of focal length.

At this focal length of 200mm and exposure time of 3 minutes, the mount had to be fairly accurately polar aligned. In this case, polar alignment was accomplished with a polar-alignment scope. Drift polar alignment was not necessary for this combination of focal length and exposure.

If you are going to use a push-pull zoom lens, make sure you tape down the zoom as well as the focus because the focal length can change if the zoom moves during the exposure. This can happen very slowly during the exposure just from the weight of the optical elements in the lens.