As stated many times, a telescope is only as good as its mount! You can have amazing optical quality, but if you can’t get the object centered, let alone find it, then the mount makes the telescope useless. But there are mounts that are designed for different things, and it’s important to know which does what, so you, the telescope buyer, has the idea.
Alt-Az Pros and Cons
Alt-Az is short for Altitude – Azimuth. Of the two types, this one is the simpler type to use, considering the two axes are your standard directions. The Altitude axis is your up and down movement, allowing you to get the telescope pointed as high as you need it, while the azimuth axis is your left and right movement, allowing you to point the telescope in any direction at will.
Pro – Portability and Ease of Set Up
Most Alt-Az mounts are simple open fork mounts that don’t have to worry about counterweights, which make the set up much lighter and more portable. Even larger Dobsonian mounts are much easier to set up, which gives you the power of a larger telescope with the portability of a smaller telescope.
Pro – Scanning the Sky At Low Power
On your Azimuth axis, you can have the telescope pointed straight at the horizon or below, and move along the entire horizon in a complete circle!
As such, you can get your telescope pointed in the direction of the object along the azimuth axis, and then use the altitude axis to get it at the correct height. This makes finding bright objects easy at low power, and the movement of the telescope feels much more natural to the directions you’re used to.
Con – You Cannot Track That Well at High Magnification.
While finding the object is easy, staying on the object is another matter. It’s not as big of a deal at low magnification, as the apparent movement is slow and easy to follow, but when you get into higher magnification, the movement due to Earth’s rotation is much more obvious, and you may get a few seconds before you have to re-center the object.
Since Alt-Az mounts are not designed to move along Earth’s rotation, manually tracking at high magnification can be a chore!
However, Alt-Az mounts equipped with Go-To systems solve that problem!
Con – By Default They’re NOT the Best Option for Long Exposure Photography!
Getting lunar shots and filming short “movies” for stacked planetary shots is still possible, but long exposure? Not so much.
Even if you had automated GoTo Software equipped with an Alt Az mount, You will still have to deal with field rotation – while the telescope will still track the object, over time the objects in the FOV will appear to rotate, thus the stars will appear to form circle trails in long exposure. This means the longest you can do before the rotation is about 15-20 seconds.
Is there a way around this? Yes, but it takes a lot of work, patience, and processing! You’d be diligently taking dozens to hundreds of sub exposures at 15-20 seconds each, and then stacking/aligning them. I know it’s possible because I’ve met people who have taken great finished shots using this method.
Equatorial Mount Pros and Cons
The two axes on an equatorial mount are your Right Ascension and Declination. RA is your east-west movement, but is essentially your axis that matches the object’s paths with Earth’s rotation. Your Dec axis is your north-south movement, which helps you find objects based on their positions north or south of the celestial equator.
Equatorial Mounted Telescope
Pro – Their Design Makes Manual Tracking Much Easier!
Because an equatorial mount is designed to move along with the Earth’s rotation, they give you much more time observing the object rather than readjusting. When set up and correctly polar aligned, even non-motorized equatorial mounts will only require you to readjust on one axis, and it will just be a simple twist of a fine adjustment control!
Pro – They ARE more suited for Long Exposure Astrophotography!
As such, when you have an equatorial mount equipped with a motor drive that automatically moves the telescope along the RA axis, this gives you the capability for long exposure astrophotography! Unlike Alt-Az mounts, you don’t have to worry about field rotation, as the mount keeps the field of view angled the same way no matter how long.
Depending on how well aligned your mount is, and how good the guiding is, you can easily get the desired exposure times you want. Even if you’re dealing with a max exposure time before your “mistakes” start to show in the exposures, it’s still way less sub exposures and stacked images than you would if you used an Alt-Az mount.
Pro – Learning Coordinates and Using Setting Circles Help Precisely Locate Hard to Find Objects
While Alt-Az mounts are technically easier to move and point, they won’t help when trying to precisely locate a deep sky object. That’s where using the celestial coordinates come in, and equatorial mounts are designed with these in mind! For more explanation, read Using the Setting Circles on a German Equatorial Mount.
Con – Their Tracking Capabilities Only Work IF Properly Set Up!
Equatorial Mounts require polar alignment, and thus you need to learn how to do it. Even if you have learned the steps, getting it as aligned as possible still takes time to set up, and even then there can be a margin of error, which does affect how long an object stays centered in the eyepiece, and how long of exposure you can realistically do before the stars start showing trails from drifting off.
Con – They’re Not as Portable and May Feel Awkward!
Equatorial Mounts have counterweights that keep the telescope balanced. Depending on the size of the telescope and mount, these counterweights can be heavy, making the entire set up heavy to move once fully assembled.
Moving an equatorial mounted telescope can feel awkward as well, since you’re not moving along the straight directions you’re used to. Relative to an Alt Az mount, an equatorial mount moves in diagonal directions, especially when fine adjusting, so even if you’re moving up, you could also be moving to the right.
Other Not As Important Points
- Telescopes with equatorial mounts have difficulty finding objects near the celestial poles, while Alt-Az telescopes have difficulty staying with objects near the zenith.
- Alt-Az mounts are also good for terrestrial observing, while equatorial mounts make it awkward due to their design.
- Equatorial Mounts take longer to set up versus Alt Az mounts.
- Alt Az mounts can become equatorial mounts with the addition of a “wedge.”