The Shorty Plus 3-Element 2x Barlow was an accessory I decided would be a sensible and immediate addition so as to make better use of the two standard eyepieces supplied with the Orion XT10.
A Barlow lens is a very useful item, and I constantly make use of it now, with all my 1.25" eyepieces. Basically this provides 2x magnification to anything you use it with, so effectively the 25mm eyepiece which has (1200mm / 25mm =) 48x magnification can now also give 96x, and the 10mm (1200mm / 10mm) = 120x, so you get 240x with the Barlow.
Not only does it provide double the magnification for each of my eyepieces, it can also attach to the 1.25" nozzle of my webcam for astrophotography.
The full Moon is an incredibly bright object on a clear night.
Through the XT10 it has a very white surface, and can literally be almost too much to look at. If all you want to look at on a given night is the moon then you can look at it directly through the telescope, but it can be quite uncomfortable at first until your eyes iris closes down and gets used to the brightness. Looking at the moon like this will ruin any chance of seeing dim stars later, for a good half hour or more. That's why a moon filter is usually used to lessen the brightness, and it will increase the contrast of your view.
A 13% density moon filter was an additional item that didn't cost too much, so I decided it would be a handy accessory. It simply screws into the bottom of the eyepiece you use.
IntelliScope Computer Object Locator
The IntelliScope Computer Object Locator unit (COL) was, for me, always on the cards as not just "an optional accessory", but more of a neccessity.
While I do know my constellations and major stars fairly well, I certainly would not know at any given time where to point the telescope to view the planets, clusters or DSO's (deep sky objects).
Since owning and using my XT10 for 4 months, I think the computer object locator is great! It's very easy to setup and use, and is a godsend when it comes to repositioning on an object you may have been observing, but has since moved out of view (remember that the XT10 has no motors to track an object, so getting back to something easily is very important, particularly on DSO's or when zoomed very close into planets at high magnification).
If you've already read my comments about the, err - "buttery smooth azimuth bearing" (!), you'll understand why sometimes the COL comes in very handy if you've overshot an object while trying to track it. Sometimes you overshoot but you totally lose where it was in the eyepiece, and the COL helps you get back on track again.
The other attraction of the COL for me is its ability to integrate with some astronomy software packages to show what part of the sky the telescope is pointing at, on the display of your laptop computer.
Metal Holster for the COL
The metal holster can be screwed to the Dobsonian mount, usually on one of the upright stand sides. The Computer Object Locator simply slips in and out of the holster for quick and easy access.
It is made out of folded steel, so it is rock solid, and finished with black paint.
It's quite expensive for what it is! But serves its purpose.
Some people use velcro instead to stick the COL either to the stand or even to the telescope tube. I think velcro would be too sticky, and removing or replacing the COL to the velcro would likely move the scope again after you have aligned it. With the holster you can gently lift and replace the COL without disturbing the direction of the telescope. That is quite important if you later modify the azimuth bearing to use a Lazy Susan turntable type ball-bearing, which makes the scope rotate very freely!
Other Topics in the Assembly section: