Nanotracker - peak-to-peak of 280 arcseconds??
Posted 09 February 2014 - 07:42 PM
What I get is:
- one period per 30 minutes
- 15-16 pixels peak-to-peak
This means (according http://www.astro.sho...lc.htm#details) that the peak-to-peak error of the mount is around 280 arc-seconds??? Anyone care to check my computations?
This is a horrible horrible error. I have seen other sites in Japan measuring it at +-2.5 arcminutes but I couldn't believe it until I tried.
Posted 09 February 2014 - 08:26 PM
Posted 09 February 2014 - 09:36 PM
this is the type of mount revolution that mmalik is looking for
Posted 09 February 2014 - 10:47 PM
Posted 09 February 2014 - 10:53 PM
Seriously. I have an answer to this which is "revolutionary."
Put a $10 Bourns 8-bit absolute encoder on the worm shaft. Now you can index the worm position and apply a PE correction at the factory (since the encoder is absolute). You'd need a processor (rather than a dumb quartz-driven stepper motor controller) to read the encoder and apply PE corrections, but we're talking another $10 in parts here.
et voila. Probably sub 10" p-p periodic error.
Now that's revolutionary, because it leverages cheap electronics to address a horrible mechanical problem.
Posted 09 February 2014 - 11:12 PM
Posted 10 February 2014 - 12:18 AM
Posted 10 February 2014 - 05:03 PM
Posted 10 February 2014 - 10:33 PM
I suppose it is just all right for taking short exposure wide field image of the night sky and cannot expect too much from such a small unit.
K W TONG
C8+CG5 GT, TSA102+HEQ5 PRO, MK67+Voyager, NexStar 6SE, C5+Mizar K, WO ZS80FD+Kenko NES, Megrez 72FD+Kenko KDS, Mini Borg 50, PST
Posted 11 February 2014 - 12:16 AM
Posted 11 February 2014 - 01:25 AM
Posted 16 February 2014 - 09:17 PM
And in the end, I tried again, and I recorded a PE of...... 280 arcseconds.
OK, I'm dropping the ball on that one. At least it seems this device has everything done to make the PE as "small" as possible at the factory...
Posted 17 February 2014 - 11:34 AM
Even worse than 2 minutes. The period being 30 minutes, one peak to the other will be done in 15 minutes. So an average deviation of 18 arcseconds per minute - and my resolution at 50mm being 18 arcseconds per pixel... I'm already toast! I'd say that close to the peaks, my subs would be good, but in the interval subs will get back. So throw away around half of 1min subs at 50mm? Not glorious
The extemely long worm period works in your favor provided the other gears do not throw in really large and fast PE of their own. It is possible you might be able to go greater than 50mm and still have only a 50% throw away rate. Have you tried 90 or 120min subs with the 50mm, you may still only have 50% throw away rate if you are lucky. Looks like it will do well around 28mm or less. Should not take long to image the entire sky!