by David J. Watkins
Astrophotography Aquiring Images - Locating Your Target
If you are using a GoTo system, then you will first want to perform the alignment either 1, 2, or 3 star. Sometimes it helps to first perform a one or two star alignment before performing the three star alignment. The (1, 2, or 3) star alignment for the GoTo system, aligns its internal map of the sky in the handset, with the actual position of the stars selected during the alignment process. Once aligned the GoTo mount can find and closely position on any object in its database. Obviously a three star alignment is the most accurate. Sometimes a two star alignment will be close enough.
GoTo mounts typically have tens of thousands of objects in their database. You simply select the object that you wish to view, and the mount will slew to that object. In reality, you still need to sort of know your way around the sky, as it does not always put the object in the view of the eyepiece, especially on longer focal length scopes. It will get you close, but not always close enough. This can be frustrating if you are trying to image something that you cannot see through your scope. Often times I find myself taking many test images with long exposures to see if the object is even in the view. When the GoTo is on, it usually will put the object in the eyepiece, though it may not be centered exactly. Reasons for not being accurate might be if you bump the mount, if either of the clutch adjustments for RA or Dec axis are loose, or if the mirror on an SCT scope shifts position. Sometimes performing another 3 star alignment will put things close again.
If you know your way around the sky or if you are just imaging a planet, you can skip the star alignment (not using the GoTo feature), and just manually slew your scope to the objects then set the tracking mode to sidereal or lunar, depending on what you are tracking, and the mount will track your object. I never perform the star alignment if I am only imaging or viewing the larger planets, the moon, or the sun.
Since I started using a Telrad Viewer, I rarely use my finderscope. Before you can use a finder scope you must first align it with the telescope. I usually try to do this in the daylight by pointing the telescope to a distant object like a radio tower, then center it in the telescope eyepiece, then adjust the finder scope so that the tower is centered in the finder scope as well. If you have to align it in the dark, planets or bright stars like Vega work the best.
Once you have aligned the finder scope with your telescope you can slew your telescope close to the object you want to view, then use the finder scope (since it has a much wider field of view) to position the object so it is centered. Then the object should be centered in the telescope eyepiece as well. This works well for bright objects but does not work so well for Deep Space Objects that are dim and difficult to see in the telescope.
Just like a finder scope, before you use the telrad viewer, you must first align it with the telescope. I use the same method mentioned for aligning a finder scope.
I use my Telrad viewer often. The telrad viewer is just a projection system that projects a cross-hair pattern (and concentric 2 and 4 degree circles) on a piece of glass that you look at the sky through. There is no magnification and the view is exactly as it is in the sky. The telrad viewer appears to be placing the cross-hairs in the sky. I find this to be the easiest way to position objects in the eyepiece of the telescope. I typically use the telrad viewer during the three star alignment of the GoTo system. I also use it to find planets or bright stars when not using the GoTo system, and will use it if the GoTo system is not perfectly aligned. One thing to note is the telrad viewer is the first thing to collect dew, so you should get the dew shield for it if you get one. And just like the finder scope, it works best using bright objects. You can use it if you know about where a dim object is in relation to other bright objects. I have used it to locate the Ring Nebula (M57) by first finding Vega, then navigating through the parallelogram in Lyra to the location where M57 should be.
A green laser pointer works best for pointing out locations of objects to a group of people. It's not really the best method for attaching to the telescope and locating objects. For one thing the lasers will typically still cast an intese light 4 miles away, some will work much further. It can be dangerous as in temporarily blinding a pilot if you shine it in the cockpit of an airplane or helicopter. You will likely attract the attention of the police if you keep shining it near aircraft and may end up in jail or have to pay a large fine. Another problem is as the temperature gets cold, the laser will quickly lose power unless you heat it.
Learning to use a star chart is probably a good skill to have. It is confusing at first, as east and west are swapped from how you would think they should be. I hardly use my Sky & Telescope Pocket Sky Atlas, probably because I am spoiled by the GoTo mount. So I never have mastered the skill of using it. Maybe one day I will!