Thursday, July 24, 2014

Sky Watcher Star Adventurer Portable EQ Mount

I purchased this portable mount in London from The Widescreen Centre in London (very close to Baker Street!) instead of lugging my old Vixen Polaris to the UK.  I got the "Astro-Photo Bundle" for £299.00 (about US$ 500) and am still waiting for the £40-odd VAT rebate, which would bring the price down to about US$ 400.  This mount is also available from Perseid in Malaysia for 1700 MYR, or about US$ 540.

The build quality is better than expected, with some nice touches such as the worm-and-sector drive for the altitude axis of the equatorial wedge, a design very reminiscent of the Astro-Physics Mach1 GTO, albeit with much slacker tolerances. There even is a ratchet on the altitude locking bolt (again, just like the AP). Here I have secured it via the 3/8" bolt to the aluminum tripod of the Vixen Polaris.  The mode dial and power switch is also visible here:



Right Ascension and Declination clutches are the large knurled plastic wheels.  On a less sturdy tripod, it is quite easy to knock off the polar alignment when tightening or loosening these clutches.


The declination slow-motion knob is visible in the photo below.  Note that the equatorial wedge, declination slow-motion, counterweight shaft, and counterweight, are all part of the "Astro-Photo bundle" and are separately priced if one purchases the base package.  On the other side of the Star Adventurer body are two electric RA slow motion switches (12X sidereal) to assist in centering objects, since tightening the RA clutch is a fiddly affair that tends to throw objects out of the field.


There is a fairly nice polar scope, although the reticle illuminator is attached to the far end of the polar scope bore, which is obstructed by the declination assembly.  Hence use of the illuminator requires removing the entire declination assembly (and any payload on top), which throws off the polar alignment.  The 4x AA batteries are under the top cover, and are supposed to last for up to 72 hours of tracking. Maybe that's with lithium batteries.


Below is a 100% crop of the area around Deneb, 2-minute exposures with a Canon 70-200mm f/2.8 lens at 200mm.  There is a bit of RA drift, and a much smaller DEC drift.  The RA drift is a combination of periodic error  and polar misalignment in altitude (as I only used the polar scope for alignment, this was in Lancashire in the UK).

Notice the nasty diffraction spikes on the bright star. A nifty trick I learned is to use a lens filter step-down ring to stop down the aperture (for tighter stars) while retaining nice round stars. If you use Canon L lenses, most of them have 77mm filter rings, so a 77mm to 67mm (or similar) step-down ring would be appropriate.


On returning to Singapore, I decided to load up the Stellarvue SV80ED, and a Meade DSI.  Widescreen hasn't received their shipment of counterweight shafts and counterweights yet, so the mount was severely unbalanced (no counterweights).


Using PHD2 I was able to measure a bit less than 2" RMS error in RA, after guiding.  The Star Adventurer has a standard ST4 guide port, but only can guide in RA, since the DEC is not motorized.



Unguided performance shows about 23" peak-to-peak periodic error, and there is no PEC.  The worm period is 10 minutes (144 teeth).  This implies that peak periodic error over a 2-minute period would be approximately 9" - so unguided exposures at 200mm and of 90-second duration should be possible at zero declination (the duration would be longer at higher declinations).

Guided performance should be acceptable at around 2" to 3" pixel scale, limited only by declination drift.  So a scope like the SV80ED would be a good choice if guided.  However, the mount is close to its limits with such a payload. A 200mm range camera lens or small refractor like a Takahashi FS60 is probably a better choice.



In summary, this mount is a far cry from my Mach1.  Although it looks better-built than other Chinese mounts, and some of the parts are CNC machined and not cast, the illusion of quality falls apart under close scrutiny.  That said, if you want something supremely portable for up to perhaps 300mm focal length, this mount will do very well.  It says something that the entire mount weighs not much more than a Mach1 Eagle half-pier (and also doesn't cost a lot more than said half-pier).

If I ever travel to Gran Canaria,  I will certainly not be able to bring the Mach1 along, but this mount will fit perfectly in check-in luggage.

I did manage to get about 30 minutes of the area around Deneb with the Star Adventurer from Lancashire, but I missed the Pelican Nebula by a small amount.  The wispy nebulosity next to Deneb that I thought was a DSO, turned out to be dirt on the DSLR sensor. D'oh!  image scale with the 200mm lens was about 6" per pixel.



1 comment:

Tomek said...

HI,

Great post! I have this mount and you are right that it is not specially price effective solution if you add a decent tripod. You are looking at $800-900 CDN. I have done some tests with PHD2, WO66SD scope and Orion TOAG (ASI120MM)
I have noticed that whole thing was flimsy and I could not polar align. Even when I was successful with the drift method any time I touched the mount the alignment was ruined. I am thinking about adding Arduino and a small stepper motor to guide in DEC as well. Have you tried it already?

Thank you!

Tom