Celestron Advanced GT C-8  (2005)

8" Schmidt-Cassegrain, f10, Starbright coatings, CG-5 Advanced Series GT mount, NexStar computer

C-8

Pros/Cons

+ Excellent optics.  Bright, very good contrast

+ Holds collimation well, I have yet to adjust it from the factory collimation

+ Least mirror shift of any SCT I've used.  Easy to focus without loosing your target and usually stays on the camera chip throughout fairly long unguided imaging sessions.

+ Comes with a usable 6x30 finder, much better than what they were providing during the Tasco days.

+/- Fair to good mount.  Not solid or accurate enough for unguided photography, but it is a major upgrade from their old Tasco-ized CG-5 mount.  Works very well with my TV-60is and a 10 second guider exposure with the ST-8E.  The C-8 tube needs guider exposures of under 5 seconds to minimize visible errors. 

+ GOTO is fairly accurate, not as fast as the LX-200, but it is not slow either.  About half the noise slewing as the LX-200.  Takes it a few seconds to finalize it's position, mostly because it overshoots in one or both axes and then slowly backs up to position to remove gear slack. 

NexStar - Pros/Cons, and how it compares to the LX-200 (classic edition)

+ The menus are mostly very intuitive.  (LX-200 menus are somewhat cryptic at times.)

- You must enter your date and time every time you start or realign the computer.  (LX-200 has internal clock circuit that keeps it's own time.)

- Only allows one location, so if you take the scope somewhere else you have to reprogram the location.  (LX-200 has five location memories.)

- It does not beep when it's done with any movement, so you have to pay attention to the display to see if it's done slewing. Using the keypad to center the object before the computer is done confuses it.  (LX-200 beeps whenever it finishes any operation.)

+ Allows you to specify an approach direction so when the slew is done the worm gears are loaded, not slack. (LX-200 takes the most direct route, so sometimes it takes a couple minutes for the tracking to settle out.)

- Requires three stars to align, a little tough with the limited horizons in my backyard.  (LX-200 can align with one or two stars.) 

+ It has four alignment modes.  The first mode it selects the alignment stars, if one is not visible you can hit "undo" and it will select another.  The second mode has you select the stars, keeping in mind that at one has to be on the opposite side of the meridian from the other two.  The third mode simply models the alignment based on your location.  If your polar alignment is not real close this mode is about worthless.  The fourth mode uses your last saved alignment.  Would work well if the scope was permanently mounted, just remember to put in the new date and time when you start up. 

2008 - Latest firmware upgrade, if you have an upgradable controller, uses a two star alignment (stars selected by you) and allows the addition of additional alignment stars.  Also has a one-star alignment for permanent setups, and solar system alignments. A quick align is available if you trust your rough polar alignment. 

If you have an older, non-upgradable, controller the ~$140 upgrade price is well worth it.  Several other features, mostly for photography and tracking/GOTO improvements have also been added.  Major improvement.

- Computer does not compensate for poor polar alignment while tracking.  To keep an item in the eyepiece for an extended time the mount must be well polar aligned.  (LX-200 does keep an object in the eyepiece, no matter how bad the polar alignment, though it will move around a fair bit if your alignment is not good.)

+ Even though it does not compensate for poor tracking it does keep track of where it's at.  When an object drifted away while I was fetching another cup of coffee, simply having the computer go back to it brings it right back into the FOV.

- Computer is not heated.  Celestron states that the display will quit working at about 25 degrees.  How often is it colder when you are using a scope?  (LX-200 has a heater circuit and has worked fine for me to just under zero degrees, then I give out.)

--- Big minus here - The hand controllers/computers are very heat sensitive.  I have two different controllers - the original (2005) and a new (2008) upgradable controller.  Both are heat sensitive.  Neither will work on a hot day.  Not an issue at night, but I also enjoy solar astronomy and it is a real pain when the mount won't start up and track the Sun.  (Never have had trouble using the LX-200 during the hottest days, even with the scope in a astro tent that is even hotter than the ambient air temperature).  It seems the motor controllers rely on the hand control for their basic instruction and with out the hand control working the motors remain idle.

- Short cord only stretches to about two feet.  Sounds like enough, but seems that no matter where I am looking I am stretching the cord a lot and/or reaching around the mount to use it.  Just another foot would be nice.  It is probably more than long enough for their fork mount where the cord plugs into the fork so the relation of the optical tube to mount doesn't change much.

Otherwise, the NexStar is about identical to the LX-200.  Both have several catalogs, tour modes, info modes, setups to set backlash compensations and other tracking/operational parameters, multiple manual slew/guiding rates, etc.

Got a great deal on this, brand new, from a local retailer ($300 less than the best price I found on the web).  Bought primarily to use in the backyard.  Light enough to carry in and out of the shed fully assembled.

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