Using SC4to counter image drift

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zerolatitude
Posts: 51
Joined: Mon Mar 01, 2021 5:24 am

Using SC4to counter image drift

Post by zerolatitude »

So this is a very specific situation.

1. Sky brightness at 17 or so (maybe 17.5 - 17.8 late at night if I'm lucky). So very short exposures
2. Restricted sky view between buildings. Polaris not visible. So polar alignment accuracy is limited.

So I can take several subs of max 10-15 sec each (which is incidentally very long for the sky brightness). But over a period of time, the inaccurate polar alignment results in the image drifting between subs.

My solution is to re-align every 5 minutes through a simple sequence like this
1. Plate-solve and sync the target
2. Wait 15 sec for mount to settle down
3. Take 20 subs of 15 sec each
4. Loop steps 1-3 till desired integration time is reached (in this case, looping 12 times will result in total integration time of 1 hour).

This works superbly. My sub rejection has dropped sharply and the stacked pictures have much fewer artifacts at the edges, needing less cropping. Of course, the specific numbers will vary with the mount and sky conditions.

Thanks to Robin for making this possible.
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admin
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Re: Using SC4to counter image drift

Post by admin »

Hi,

I'm guessing that this was possible using the sequencer? If so then (if you are willing to), could you perhaps share the sequencer script file for others to build on?

cheers,

Robin
zerolatitude
Posts: 51
Joined: Mon Mar 01, 2021 5:24 am

Re: Using SC4to counter image drift

Post by zerolatitude »

Sure. Its pretty straightforward.

This is the sequence for making 2 panels for Rosette - 1 hour of integration time for each panel. The "overhead" of platesolve and settling time adds about 15 min, so 2hr 15 min total.

The co-ordinates are from the NINA framing assistant. As requested elsewhere, would be great if we didn't have to convert RA/DEC to decimals (saw your reply on the file workaround, but direct entry in traditional form would be better).

I don't know how to enter a comment though. That would be nice.

SEQUENCE
PROMPT "Setting up profile. Press OK to Continue." ENABLECONTROLS True
SET COLOUR SPACE TO RAW16
SET RESOLUTION TO 1936x1096
SET BINNING TO 1
SET OUTPUT FORMAT TO "FITS files (*.fits)"
SET EXPOSURE TO 15
SET GAIN TO 65
SET OFFSET TO 25
WHEEL SELECT "Manual Filter Wheel"
WHEEL SELECT FILTER UHC
PROMPT "Rosette Panel 1: Press OK to Continue." ENABLECONTROLS True
TARGETNAME "Rosette P1"
MOUNT GOTO 6.5319 5.2972
LOOP 12 TIMES
MOUNT SOLVEANDSYNC
DELAY 20
CAPTURE 20 LIVE FRAMES
END LOOP
TARGETNAME "Rosette P2"
MOUNT GOTO 6.5319 4.5861
LOOP 12 TIMES
MOUNT SOLVEANDSYNC
DELAY 20
CAPTURE 20 LIVE FRAMES
END LOOP
END SEQUENCE
Attachments
Rosette_MultiPanel.scs
(781 Bytes) Downloaded 11 times
timh
Posts: 218
Joined: Mon Aug 26, 2019 5:50 pm

Re: Using SC4to counter image drift

Post by timh »

Thanks - just to say that it is always very useful to see lists of actual sequencer commands like that. I've always found the easiest way to get an insight and started in any scripting language is to start by adapting from somebody else' code.
TimH
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