Periodic error of my Star Adventurer
x-axis: time in seconds, y-axis: arcseconds
The peak-to-peak error of my Star Adventurer is about 87 arcsec (10 minutes period).
I did some further measurements, all with fully loaded equipment (DSLR, 400mm lens, Guidescope). The first one is done on Feb 12, 2017.
February 14, 2017, peak-to-peak: 78 arcsec (peak-to-peak) per 10min period.
April 13, 2017, peak-to-peak: 88 arcsec
April 13, 2017, peak-to-peak: 71 arcsec
I never achieved such a good DEC curve in the following measurements… the first one was a very lucky polar alignment 🙂
Curves from the 3th and 4th measurement:
Anyway. The (bad) DEC curve (peak-to-peak: 17 arcsec/period) wouldn’t be noticeable even on a 200mm, 60 seconds shot.
Regarding these values I could exposure unguided as follows with my Star Adventurer (at 0° Declination):
Dmax = P*Pi/T
Dmax is the max drift speed, in arcsec/min, P is the peak to peak periodic error, in arcsec and T is the worm gear period, in minutes.
Dmax = 71*Pi/9.97
Max Drift Speed: 22.365 arcseconds/min
Resolution formula: (Pixel Size / Focal Length) * 206.265 = arcsec/px
Example: A star moves 22.365 arcsec during a 1 minute shot. The resolution of my DSLR is 2.11 arcesc/px at 400mm focal length.
Calculation: 22.365/2.11 = 60s/5.7s
- 400mm: Resolution: 2.11 arcsec/px ~ 5.7sec exp.
- 280mm: Resolution: 3.02 arcsec/px ~ 8.1sec exp.
- 200mm: Resolution: 4.23 arcsec/px ~ 11.3sec exp.
- 100mm: Resolution: 8.46 arcsec/px ~ 22.7sec exp.
- 50mm: Resolution: 16.91 arcsec/px ~ 45.4sec exp.
(Canon EOS 70Da pixel size: 4.1 micrometer, Astronomy Tools Calculators)
My Star Adventurer performs bad after 2 years heavy use… On the net some other Star Adventurers have around 50 arcsec peak-to-peak PE.
I really thinking about a new SA 😉 A comparison between a brand new and a 2-year-heavy-use Star Adventurer would be interesting…
Used equipment in this video:
- Star Adventurer Mount (~2 years use)
- Lacerta MGEN-II AutoGuider
- Orion 50mm Mini Guide Scope (162mm focal length)
- Mounted EOS 70D with EF 400mm lens
- MGEN Windows Application
- Microsoft Excel
Setup Star Adventurer and start star tracking.
1. Setup MGEN
- Set date and time (it creates the file timestamp).
- Next create and open a new file.
- Go to guiding menu and search a star near to 0° Declination by aligning the guide scope.
- Go to page 5/5 in Guiding Menu and select “more..”
- Enable “Save pos.”. From this moment the absolute position of the star is beeing recorded.
- Wait at least one worm gear period (Star Adventurer: 10 minutes)
- Disable “Save pos.” to stop recording data.
- Close the file
- Power off MGEN
2. Download data from MGEN to PC
- Connect MGEN to PC via USB and power on the MGEN
- Start Lacerta MGEN PC app (download here) and go to “File control”
- Select file and set parameters. Check at least “Generate Periodic Error” and set focal length of your guide scope, worm gear period of your mount and the star’s declination coordinate.
Then click “Download + process file(s)”.
3. Create Graph (in MS Excel)
I used MS Excel to create a graph. Excel interface only in German… sorry.