Error difference between a manual pointing file and Sequence and MLPT

[rharter]

Hi all,

 

After a successful repair of my DDM85, I have made a manual pointing file with 18 stars (e+w). Everything looked good, even after the meridian flip the star was almost in the field of view with almost the same deviation. The first test shots worked until 10 min at different declinations. After that I made a Sequence Mouse Grid pointing file ​​with about 40 stars (e+w), error at about 4 arcmin in RA and DE ! Tracking only until 1 min possible. Also MLPT error (RA, DE) at 3 arcsec. I do not understand why this glaring difference between the manual pointing file and the automated methods is possible. Second attempt, after a restart, same game. My manual pointing file is functioning properly. At the zenith 15min is possible. Sequence auto pointing failure is much too big. MLPT sometimes worked until 8min but not always.
I cannot see a pattern when and what works where? Itself the originally good manual pointing file also does not always work properly.
Anyone had similar problems, even with the manual pointing file that it works on one day and the other not ?
I must admit that I expected a lot more from Sequenze and MLPT. Where does the much larger error compared to the manual pointing file came from? Would anyone have an idea how to get a little more continuity ?

 

Thanks for your help!

[RamaSpaceShip]

Hi,

 

My little experience with the DDM85 tells me that if a pointing file is good one day and bad another, this often means that something is moving in the mechanical setup. In my case it was the dovetail screws which were not tightened enough. But it can be anything else in the OTA.

 

You need first to verify every screw or similar. Check also your pier if there is any chance for it to cause the move.

Don't be lazy, even if it appears very surprising, the evil hides there.

 

 

Good luck and happy new year.

 

Bernard

[gmalits]

Hi,

 

as Bernhard mentioned, ...so tell us a little bit about your equipment (optics) are there "moving parts" like a mirror who shifts in an SCT, or similar?

[rharter]

Hi Bernard,

Hi Gerald,

 

A 14" ODK and a 70mm refractor are mounted on the DDM85.

Of course, moving parts are a tremendous source of errors. But is it not contradictory that the

tracking with the manual pointing file do work in principle (at least up to 15min without tracking

problems) and with Sequence actually does not and limited with MLPT?

kind regards

Ralph

[RamaSpaceShip]

Hi Ralph,

 

It is not evidently contradictory. The move may occur when the mount is under the control of Sequence, due to some movements that only Sequence do. Or the move is due to a vibration that occurs because the link between your two OTAs is too soft and Sequence leaves not enough time for the vibration to cease. It is difficult to answer your question without the knowledge of what is moving.

 

As I already told you, you need first to verify each screw, including the pier screws, the tube rings screws, the OTA screws, and the refractor link screws.

Once you are absolutely sure that nothing can do a move because you have carefully verified everything, then you can start looking at another issue. Nothing else can be done before.

 

You can also remove the refractor and check if you still have the problem.

 

 

Regards.

 

Bernard

Edited January 2, 2014 by RamaSpaceShip

[rharter]

Hi again,

I seriously followed your hints, but..
yesterday MLPT created an admittedly extreme tracking (see attached pic). But my problem is good visible. Previously, I had tracked in the same region with a manual pointing 8min without problems! I had previously checked all screws and parts several times for rigidity. Unfortunately I have no explanation for this and I must admit that I doupt the only explanation with loose parts. ;-)
I have repeatedly reinstalled the software several times. Does anyone else have a suggestion?

 

kind regards

Ralph

 

 

[lukepower]

Hi Ralph,

 

I once had a similar problem. I tried to solve the pointing exposures with different catalogs (GSC 1.1 is not enough for my narrow field of view) and it helped. It was then resolved once I figured out that I should aim for a perfect solve of every image - sometimes the residual error was big enough to get everything messed up. Maybe you could try with another catalog or other settings for Pinpoint...

 

Good luck

[rharter]

Hi Lukas,

 

your hint sounds quite plausible.

If I want to use e.g. the UCAC4 how is it possible to use it because Sequence 0.9 does not list this catalog in the reference list?

 

Kind regards

Ralph

[lukepower]

Hi Ralph,

 

personally I switched to USNO A2.0 because it's denser field. UCAC3 was usable only by editing the Sequence ini file (can't remember exactly what I had to set, though), there is a setting for the catalog type which is passed to Pinpoint.

by the way, I uploaded the A2.0 catalog as a RAR file on my homepage (http://www.astro-dolomites.com/the-observatory/downloads/), maybe it's helpful for all those not wanting to download from the extremely slow Flagstaff Station FTP server.