Refractor Telescopes
Increasing overall quality refractors, at increasing prices:
Celestron AstroMaster 70AZ Telescope
Celestron Inspire 100AZ Telescope Built in mobile phone adapter for imaging
One problem that novices have is pointing the telescope to an object you’d like to view. With their StarSense product and included finder scope, Celestron now makes this task easier with several refractors and Newtonian reflector telescopes:
StarSense Explorer DX 102AZ Refractor
Astro-Tech, based in Oklahoma, manufactures and sells telescopes (mostly refractors) direct to consumer. I do not yet own any of their telescopes, but they have an excellent reputation for quality and value. Currently selling for just over $400, this doublet refractor looks good and is a great value:
Moving up the price and quality scale, these appear to be a good value among refractor:
In general, the wider the diameter (aperture) of the telescope, the more rapidly light will be collected. And, other factors being equal, the longer the focal length of the telescope, the more detail will be present in the image. Additional factors, such as the quality of the glass in lenses, can have an appreciable effect on the image. Some glass, and some coatings applied to the glass, can dramatically reduce chromatic (color) aberration. Also, different scopes have different susceptibility to be out of focus at the edges of the image. Telescopes with “field flattener” attachments reduce this problem, as do scopes with multiple lenses designed to reduce this problem.
Reflector Telescopes
The value of wider aperture and longer focal length that we saw with refractors applies to reflector telescopes as well. This telescope design uses no lenses (except in the eyepiece), but rather curved mirrors to collect and focus the image. The most common type of reflector telescope are Schmidt-Cassegrain (SCT) designs, with Celestron being dominant in this space among manufacturers. Although the design has its limitations, it is an excellent choice for collecting light rapidly at long focal lengths. Accessory equipment, such as an attachment called HyperStar (mfg: Starizona) allows imaging at short focal lengths for objects such as nebulae and some large galaxies and, due to the wide aperture of these scopes (5 to 14 inches), the light from the image is collected very quickly. These telescopes can be unwieldy but weight is not excessive for most people.
The classic, with the greatest sales over many decades, is this model:
I have owned and operated that scope for about 12 years and am happy with it. One problem (apparent in the Andromeda Galaxy image in the Gallery) is distortion at the edges of the image. Celestron has greatly lessened this problem with their “EdgeHD” line of SCTs, but the cost is significantly higher. For example,
Celestron EdgeHD 8 (optical tube assembly only–no mount)
All-In-One Telescopes
In recent years, several telescope makers have marketed products that are self contained refractors, with much less complexity for the novice astrophotographer. Their capabilities are limited but work quite well for certain targets. Their strength–simplicity–turns out to be a limitation if you want your astrophotgraphy skills to grow beyond the limits of these devices. If instead you build your system in steps, you will have more flexibility for your growth, and you will develop an appreciation for the multiple separate tasks involved in astrophotography that the integrated systems do for you automatically and inflexibly. That being said, these systems can be relatively inexpensive ($350-$600), and might therefore be a great introduction to the hobby. Here are a few examples:
ZWO SeeStar S30 ($349, to be released November 2024)
These automated scopes track the curved movement of night sky objects as they slowly move across the sky. Star tracker devices do so as well, but are generally not suitable to handle the weight of a telescope. Telescope mounts also track celestial objects reliably despite the weight of the telescope.
TELESCOPE MOUNTS
A telescope mount is a device that moves the telescope to a specific target in the night sky. Because celestial objects move slowly throughout the night, the mount also moves the telescope slowly in order to keep the telescope locked on the target over time. When photographing a small target like a planet, given the small field of view necessary to see significant detail, the planet would move in and then out of the field of view in 10-20 seconds. This would make the photographer constantly have to re-center the planet for every 10 second burst of images recorded. Difficult to do, but it could be done. A mount keeps up with the movement of the planet and, if initially aligned correctly, keeps the planet more or less centered.
Mounts are essential in imaging deep sky objects. Because the faintness of these objects, the camera must be programmed to take very long exposures–such as 50 consecutive images of 3 minutes for each exposure. Using software, these 3 minute “sub-exposures” are then superimposed (“stacked”) on one another to bring out details of the target.
There are two main types of mounts: Altitude/azimuth, and equatorial. Alt/Az mounts track by making a series of straight-line movements in two dimensions according to the object you’re asking it to track. Over the series of sub-exposures taken, the target will rotate in the field of view, but the stacking software can compensate for this by de-rotating each frame according to alignment of the same stars in successive images. Equatorial mounts, on the other hand, move the telescope along a curved line. The shape of the curve depends on the observer’s latitude, which must be entered when setting up the mount. The movement of the telescope along a curve–the same curve that the target takes–means that there is no rotation of the target in successive images.
Alt/Az mounts are slightly preferable for visual observation, because the eyepiece stays in the same orientation relative to the telescope. And, if you plan to photograph only solar system objects, an Alt/Az mount is perfectly acceptable. For longer duration imaging of deep sky objects, equatorial is preferable for the reasons noted above. For visual observation through an eyepiece, the observer with an equatorial mount may be required to make some contortions in order to look comfortably through the eyepiece.
Star-trackers also track night-sky objects for photography but have limited load capacity. They are another option if you plan to take only wide-field images with a DLSR equipped with a telephoto lens. You should be mindful of the weight capacity of these devices, especially if your camera, telephoto, and other necessary equipment is heavy.
Below are examples of star trackers and both types of mounts. Many medium to higher-end scopes are sold with a suitable mount, either Alt/Az and equatorial:
Star Trackers
Sky Watcher Star Adventurer 2i
Telescope Mounts
Some of these are altitude/azimuth type, equatorial type and combination mounts:
Next, let’s look at dedicated astrophotography cameras.