Observing with a Tak FS-102/Vixen Great Polaris/SkySensor 2000

by Ray Gralak


I took out my Takahashi FS-102 refractor last night for some backyard observing in San Jose. My intent was to determine if I had resolved a problem with my SkySensor 2000/Vixen GP mount. At my last visit to Fremont Peak the gear came loose on the motor driving the right ascension axis of the GP mount. The solution was simple... simply to tighten a set screw that had come loose. I also took the time to adjust the backlash for each axis.

You don't need to polar align the GP mount to get good accuracy with the SkySensor, but I always roughly polar align it. When you turn on the SkySensor it asks you to move the scope until it is pointing to the western horizon. Having a known starting point allows the SkySensor's internal algorithms prevent cord wrapping and possible contact between the scope and the mount.

I find that I can achieve 1-star alignment easier if I use a level to help position the scope at a "virtual western horizon". I can choose any reference star with the hand controller and the SkySensor points the scope pretty close to the star. I then can center the star and press the "align" button. The SkySensor is then "1 point aligned". You can then follow up with a second star to get 2 point aligned. Once you reach two-star alignment it is easy to get to 3 point alignment as the mount will almost center the third object when you slew to it. You can add more alignment objects later but the mount always uses at most three points to maintain alignment. It increases the resultant pointing accuracy if you use a high powered eyepiece or an eyepiece with cross-hairs to accurately set alignment points.

As an aside, I was curious why the SkySensor displays "N point aligned" so I looked in the manual. The answer is that you can align on land objects as well! There is a database to store such land objects so you could align the scope in daytime. I guess you could then slew to the sun, the moon, planets, and even bright stars and other land objects.

I used Saturn, Rigel, and Pollux as alignment objects. Once I had the scope "3 point aligned" I could move all over the sky and have each object virtually in the center of the eyepiece at low magnification (23 x) or in the field of view at a much higher magnification (164x).

My first object was the moon. It was very low and a thin crescent. I didn't try high magnification on it but I did notice Mars next to it (maybe 1 degree away) and in the same field of view. Jupiter was even lower and to the left of the moon. Again Jupiter was so low I didn't even bother to use higher magnification than 23x.

Next stop was Saturn. At 164x Cassini's division was noticeable when the seeing steadied. The seeing, by the way, was not too bad from my backyard. Pretty good, actually, for a winter evening.

I went on to M42 and even at 23x the Trapezium was clearly resolved. To get this magnification I use a Panoptic 35mm eyepiece. The star fields produced with this eyepiece are excellent in this Takahashi FS-102. Although I still see a little astigmatism near the edge of the Panoptic's 68 degree field of view, the stars are much sharper than they were in my Traveler with this eyepiece. This is probably because the FS-102 is an F/8.1 while the Traveler is an F/5.8.

On the other hand, I think the color correction of the Traveler is superior to that of the FS-102. I never noticed any color when looking at stars with the Traveler, but I noticed a violet tinge around Rigel with the FS-102. I think this is because the FS-102 has only a two lens objective while the Traveler has three lens. I did notice that I could easily see Rigel's companion star, which has been difficult in my 17.5" even with an aperture mask. I moved on to Castor for the first time with this scope. At 164x the FS-102 split it easily with lots of space in between.

I've had my SkySensor 2000 for about 2 months during which time I've used it perhaps half a dozen times. I can now navigate well through the menus but I am still not always pushing the correct button to get the scope to move the way I want it while looking through the eyepiece. I guess I'm used to way the dob-driver on my 17.5" moves. The most annoying thing about the SkySensor is that it makes a lot of noise at maximum speed, although I'm not sure if it makes more noise than a Meade LX-200 mount. I'll have to try setting up next to Bill Arnett sometime :-) However, like the LX-200, you can reduce the maximum slew speed and dramatically reduce the amount of noise it makes. I'm always in a hurry, so I like to use it at the maximum rate (2000x sidereal) for slewing.

Next I tried for some Messier objects. M44 was low and in the arriving clouds so I couldn't see it. M1 was centered and easily visible. The Sky senor also nicely centered M31 and M32 at 23x. M33 was visible, although I might have had a difficult time noticing it had I not known that it was centered in the eyepiece. M35, M36, M37, M38 where all nice and again well centered. I could just make out the dim companion NGC cluster near M35.

As a relative novice to equatorial mounts it was a pleasure selecting an object from the SkySensor's menus and pressing "GOTO" to get to it. I find that using an alt-az mount is simple compared to an equatorial to locate objects. Maybe with more experience (and a finder scope :-) I would feel differently.

Next I went back to Saturn and tried the highest magnification I can achieve with the eyepieces and barlows I have (405x). Saturn was holding up very well at this magnification. At times Cassini would become visible, but it was obvious that this was too much magnification for this night. I did notice the sky immediately surrounding Saturn was a little brighter. I don't know if this halo is normal or not. I don't remember seeing this effect with my Traveler. It might be the eyepiece, barlow, or diagonal. I'll have to check them in the daylight.

One last thing that I noticed was the color of Saturn. Saturn looked a very "earthy" yellow. I don't remember its color being as vivid with my Traveler.

Around 7:30 I packed up as the clouds where now covering most of the sky. I missed Mir and the space shuttle as I didn't know until later they going to be visible. The SkySensor has the ability to track artificial satellites, but I haven't even considered trying that yet!

Overall I'm very pleased with the performance and features of the SkySensor 2000. For sum of its cost and the mount's (thanks John!) I could have almost bought a GM-8, which I'm sure is a much more stable mount. However, at its base level the GM-8 does not have slewing, built-in encoders, and versatile and feature-laden control firmware.


Posted on sf-bay-tac Jan 30, 1998 19:52:35 PT
Converted by report.pm 1.2 Feb 20, 2005 09:01:23 PT