Alt-azimuth mount
As I promised here, today I will present the alt-azimuth mount, why it’s good and why it isn’t for astrophotography.
The main difference between equatorial mounts and alt-azimuth mounts is the direction of moving of axis. While at equatorial mounts one (R. A.) axis is parallel to the Earth’s axis of rotation at alt-azimuth one axis is always horizontal and another is vertical. In the beginning it’s much more friendly for the user since it’s very easy to use but for astrophotography is practically useless. A lot of telescopes for visual astronomy comes with alt-az. type of mount. When we are watching an object and we don’t have a drive installed on our mount for automatic slewing we usually move the object in the center of the field, observe it for minute or so and then we move the telescope again. But that doesn’t work for astrophotography because the tracking has to be smooth and constant.
Another problem is that there alt-az. mounts are always less precise because the both axis has to be moved in the same time and that means that the controller has much more work to do and that every single moment the star has different direction and relative speed in the sky.
The last but not the least problem is field rotation wich occurs due to relative spped of the stars mentioned above. As we know the stars are virtually moving around the northern and southern celestial pole and when we have rotating the objects that are more distant from the centre of rotation are moving faster. And that occurs at alt-az. mounth that when we do some minutes long exposure – the stars in the centre of the field are sharp but on the eadges they looks loke they are rotating around the centre of the picture.
To conclude, if you like just to observe the sky the alt-azimuth mount is a good idea since it is easy to use and easy to build (it’s not expensive). But if you are planning to do the astrophotography then youhave to avoid alt-azimuth mounts.
Thanks for reading!
Image source: See Viewo
Recent Comments