Tuesday, March 18, 2014

Review of the Bushnell NorthStar 78-8890 90mm Catadioptric Telescope

Last weekend I picked up a Bushnell NorthStar 90mm Catadioptric Telescope for a reasonable price of $150 off of craigslist.


I bought this with the idea of a cheap "goto" scope that is small and very portable.

The downside was that, though it is a motored scope, it cannot be used in the equatorial mode.

The upside is that the scope can be removed from the mount and mounted on a tripod via the typical tripod socket and used as a super long telephoto with the addition of a t-adapter. In addition it can accept my 0.5x Focal Reducer 1.25" which both reduces the power and lets in 50% more light. I also have in mind to piggyback this on my Celestron C8 scope as it is reasonably light.

As is, it produced a good image but upon further inspection it was out of collimation
Since the from secondary mirror can't be adjusted I checked out the back cell and found there were three Allen wrench screws that adjusted the back mirror.  I inserted a home made plastic cap with a tiny hole in the center.

By making tiny adjustments I was able to bring it closer to collimation.  But when I inserted the right angle mirror it appeared to be out of alignment by a big amount! What happened?  Upon more inspection I found that the rights angle unit fits too loosely in the rear cell and when secured by the two set screws they pushed the unit out of alignment.

By adding a few small strips of ordinary tape to one side of the unit and spinning the screw housing around 189 degrees it brought it back into collimation!

Now I can take it to a more precise collimation with higher powered eyepieces.

As for the "goto" part of the mount... not so good. Even when I selected and followed the directions (what there were of them would be confusing for an absolute newbie) when I asked it to go to a known planet or star... it missed it by enough that even the low power 25mm eyepiece wasn't even close. If you didn't know where the object really was, you would be lost.

Anyway, the optics are more than acceptable and I look forward to using it as a guiding scope or a quickie scope (I will have to do the pointing) for an "out and in" session.

Here is where you can download the manual for this Bushnell NorthStar 78-8890 90mm Catadioptric Telescope

UPDATE: One nice thing about this scope is that the tube at the back of the scope that holds the eyepiece only needs a T-adapter that is made for one's DSLR camera. Since I have a Canon DSLR all I needed to use the scope as a telephoto was a Canon T-adapter (like this one from Amazon.com).


2 comments:

  1. I too have this telescope and own a DSLR. I am looking for a way to take pictures through the telescope. I am trying to figure out what pieces I would need to buy. Would you be able to post links for what accessories you purchased and what worked for you?

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  2. I updated my page to place a link for the only thing you should need! Clear skies!

    ReplyDelete