K3's AstroPhotography
"When I consider your heavens, the work of your fingers, the moon and the stars which You have set in place, what is Man that You are mindful of him?" -- Psalm 8:3,4

Vixen GP-DX equipped with Astromeccanica's DA-1 drive system

Vixen GP-DX (Great Polaris - DeLuxe) equatorial mount is very well-known mount in the world. It can hold accessories up to 10-11kg and provides high tracking accuracy.

1, Making decision about suitable mount type and motor drive system
2, The first tests
3, DA-1 detailed review

1, Making decision about suitable mount type and motor drive system

The rivals ;-)
  After a year of deepsky astrophotography with my entry level GEM1 mount, in September 2002 I started to contemplate about a better mount.
Here are the reasons:
1, GEM1 mount has high periodic error - up to +/- 40arcsec (80arcsec peak to peak). You can do a lot of nice photographs also with GEM1 (see my Messier catalog - all photos till the start of November 2002 were done with GEM1!), but there is a problem with number of useful frames. When I used 20second exposure in prime focus, I could use only 25% of frames (frames without star trails)
2, Modified GEM1 mount with autoguiding system was my substantial step forward in deep-sky imaging, but the whole setup (8" Newtonian + 80mm guide scope) was rather big for my balcony, demanding on setup time and lot of cables, necessity to aim guidescope, ... Furthermore, the whole equipment was heavier than 8 kg - so it was at the boundary of possibilities of GEM1.
3, As I am an employed man, I cannot afford to spent a lot of time at night by gathering useless frames, because the next day I need to wake up to office ;-).

Then I started to decide about mount type. I read many articles about Synta's EQ6 mount, but I found it rather big for my balcony and also read about problems with periodic error (about the same range as my GEM1). The most accessible mount for me in European market was just GP-DX.

Just at the same time I started very friendly communication with Paolo Lazzarotti from Astromeccanica company. I knew Paolo from my previous contact with Astromeccanica, when I searched for suitable adapter for my Nikon Coolpix 995 digital camera - they offer the cheapest adapter for Nikon in Europe!.
After some communication I came into agreement with Astromeccanica company and we did a bussiness. I provided them permission to distribute a special release of K3CCDTools for Astromeccanica and they provided me GP-DX mount with DA-1 kit.

It was very nice offer for me, because Astromeccanica is manufacturing DA-1 Dual Axis drive kit. It has reasonable price, enables computer control, autoguiding. And it has a display - I love displays ;-))). Very important feature is, that it has belt system for driving - it reduces vibrations from stepper motors (look here to learn more about vibration problem - Carsten's page about DA-1).

2, The first tests

Finally, on December the 5th 2002, my mount and DA-1 drive system arrived :-)).
The small package, but more than 17kg!
Notice the nice DA-1 controller in my hand...

Here is a table with weights of components:

GPDX+DA-1 motors 7.6kg
Vixen counterweight 3733g
Astromeccanica counterweight 4077g
Shaft 836g
DA-1 hand controller 180g
Dovetail plate (from Orion Optics) 650g

Remark: The old plate for attaching my Orion Optics scope to GEM1 mount has weight only 180g. The new dovetail plate is 530g heavier.
Dovetail plate + cradles weight is 1491g.

As soon as sky was clear, I went to balcony to do the first tests - to check this exceptional mount with DA-1 drive system.

Here is my periodic error measurement of GP-DX + DA-1 system:

Click the graph to see detailed graph.
The periodic error was measured by K3CCDTools with its Drift Explorer.
Star: Alnitak (z Orionis - DEC=-1°56'26")
Scope: 8" Orion Optics Europa Newtonian + 2X Barlow
Resolution: 0.48 arcsec/pixel
Seing conditions were rather poor, so curve is rather jerky. Seeing error could be about +/-1arcsec.
But don't forget - it is high resolution graph - with +/- 10" limits in Y axis.

I must say, I am amazed by operation of GP-DX and its low periodic error - less than +/-8 arcsec! With good seeing it would be even +/-7 arcsec. But I will have to measure it again, when conditions allows it.

The page is still under construction. New informations are continually filled up.

DA-1 detailed review

See Equatorial Mount Tracking Errors page

See Tests and Analyses of Homemade GEM1 Guiding System

See Homemade GEM1 Autoguiding Setup

Back to AstroPhotography page

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Last Update: 11.02.2003