Help please..!! Did my camera rotate during flip..?

[geoflewis]

Hi all,

I usually avoid performing a meridian flip, preferring to guide through and well past the meridian, but last night when shooting the Bubble Nebula it seemed highly likely that my camera would crash into the pier, so after 3 hours of RGB I paused SGP, performed a flip and resumed to shoot a couple of hours Luminence. It was very much to my surprise to discover that the orientation of the L images was not 180 degrees from the RGB. See below rotation necessary to align L to RGB.

Am I right in thinking that after the flip I should see images that are rotated a full 180 degrees, or have I misunderstood something? I checked the camera at the end of the session and it seems to be securely attached to the Moonlite focuser, which in turn is tightly secured to the visual back of the scope, so to say the least I am confused about what happened...

Anyway, I continued to process what I captured, so here is my significantly corner cropped final version. It is approximately 1 hour each of LRGB as I lost the sky to moonlit fog before completing the L sequence.

My processing technique needs a lot of work, but I could do without losing a lot of the data due to rotation problems - it makes me think that my avoiding flips is a good idea, but I know that I have to overcome that fear....

Your thoughts, ideas and feedback will be very welcome.

Regards, Geof

[Starlight 1]

Look in SG-Pro help I was looking at it today .

[Dave Smith]

After a flip the image should just be rotated through 180 deg so it is a puzzle as to why you have any other rotation. Is there any chance the camera is loose so that when you flip it doesn't turn relative to the scope.  I use SGP and have never had this rotation.

Dave

[geoflewis]

3 minutes ago, Starlight 1 said:

Look in SG-Pro help I was looking at it today .

Thanks I will take a look. Cheers, Geof

[geoflewis]

2 minutes ago, Dave Smith said:

After a flip the image should just be rotated through 180 deg so it is a puzzle as to why you have any other rotation. Is there any chance the camera is loose so that when you flip it doesn't turn relative to the scope.  I use SGP and have never had this rotation.

Dave

Thanks Dave,

Thanks for confirming that it should be 180 degrees rotation after a flip, that seemed logical to me, but since I've never imaged that way previously it got me wondering. I don't know what happened, the camera seemed secure, but something must have happened, so I'll just have to put it down to experience. I had my Moonlite focuser modified by Ron at Moonlite recently to incorporate a rotating flange so maybe it moved. I'll have to do some testing with flips to see what happens, maybe a cable snagged and pulled the camera, but really I have no idea as I couldn't see any cable snags. The most likely would be a pull on the cable to the guide camera as I have that securely tied to the Lodestar so that it doesn't pull free from the socket, but that would mean that any tension might rotate the whole Moonlite assembly on that new flange.

Best regards, Geof

[John78]

Did your whole scope / image train rotate in the tube rings during the flip??

[geoflewis]

45 minutes ago, John78 said:

Did your whole scope / image train rotate in the tube rings during the flip??

Hi John,

Good idea, but no that's possible with my rig as the C14 is mounted using a dovetail plate not rings. I suspect that the camera/focuser assembly rotated in the new rotating flange incorporated into the Moonlite focuser. Its convenient having that flange, but I'll need to check that its securley locked down. I'm also going to add a couple of reference marks so that I can monitor any movement should I experience something similar again.

Many thanks, Geof

[sloz1664]

If it hadn't rotated 180 degrees you wouldn't be pointing at the bubble nebula, after it's initial plate solve it would then centre on the bubble, which on the other side of the pier is 180 degrees. this points out to some movement in your set up.

Steve

[geoflewis]

6 minutes ago, sloz1664 said:

If it hadn't rotated 180 degrees you wouldn't be pointing at the bubble nebula, after it's initial plate solve it would then centre on the bubble, which on the other side of the pier is 180 degrees. this points out to some movement in your set up.

Steve

Thanks Steve,

Yep, I think it's pretty conclusive that something moved, but it's still not entirely clear to me what that was as when I checked the rig everything seems pretty tight. Hence I've guessed it's the new rotating flange on the Moonlite focuser, but that is just a guess... I'll be sure to monitor it and the rest of the camera set up closely in future.

Best regards, Geof

[sloz1664]

Just now, geoflewis said:

Thanks Steve,

Yep, I think it's pretty conclusive that something moved, but it's still not entirely clear to me what that was as when I checked the rig everything seems pretty tight. Hence I've guessed it's the new rotating flange on the Moonlite focuser, but that is just a guess... I'll be sure to monitor it and the rest of the camera set up closely in future.

Best regards, Geof

Oh the joys of Astrophotography. 

Steve

[geordie85]

My apologies to everyone who has posted previously but they are all wrong. After a meridian flip you will have a slight misalignment. 

My camera is very secure to my scope and the rotator is also very secure but I (and many, if not all others) experience this on every flip I do. This is to do with the fact that when you perform a meridian flip you aren't just flipping your sensor, but also turning your sensor. If you hold your phone in front of you (imaging it's your sensor) if you flip it 180 degrees the screen will now be facing away from you instead of towards you. To correct this you also need to rotate it. Because your camera is in a fixed position on your scope, the image will have a slight misalignment. 

Theres been a few threads here about the subject. Hopefully this will explain it better.

 

[martin_h]

5 hours ago, geordie85 said:

My apologies to everyone who has posted previously but they are all wrong. After a meridian flip you will have a slight misalignment. 

My camera is very secure to my scope and the rotator is also very secure but I (and many, if not all others) experience this on every flip I do. This is to do with the fact that when you perform a meridian flip you aren't just flipping your sensor, but also turning your sensor. If you hold your phone in front of you (imaging it's your sensor) if you flip it 180 degrees the screen will now be facing away from you instead of towards you. To correct this you also need to rotate it. Because your camera is in a fixed position on your scope, the image will have a slight misalignment. 

Theres been a few threads here about the subject. Hopefully this will explain it better.

 

Beat me to it.... There was quite a long thread on here a while ago discussing this very thing.....now can I find it?

 

[geoflewis]

8 hours ago, geordie85 said:

My apologies to everyone who has posted previously but they are all wrong. After a meridian flip you will have a slight misalignment. 

My camera is very secure to my scope and the rotator is also very secure but I (and many, if not all others) experience this on every flip I do. This is to do with the fact that when you perform a meridian flip you aren't just flipping your sensor, but also turning your sensor. If you hold your phone in front of you (imaging it's your sensor) if you flip it 180 degrees the screen will now be facing away from you instead of towards you. To correct this you also need to rotate it. Because your camera is in a fixed position on your scope, the image will have a slight misalignment. 

Theres been a few threads here about the subject. Hopefully this will explain it better.

 

Thanks for pointing (no pun intended) me to this very interesting thread. Lots of things for me to consider.....

My scope is on a permanently pier mounted AP1200, which has been reasonably accurately polar aligned (<5 arcmin). The C14 is attached to the AP mounting plate via a dovetail plate, so no rings involved which might allow some rotation slippage.

I used astrometry.net to plate solved images pre and post flip abd get the following orientation values:

Pre flip - Up is -162 degrees E of N

Post flip - Up is +5.95 degreees E of N

If I add 162 to 5.95 (say 6) then I get 168, which is 12 degrees off the expected 180, so I conclude that the camera must have rotated orientation pre and post flip.

As a test I took the TSR aligned post flip lum image into MS Picture Manager and rotated it -12 degrees; sure enough that brings the long edges of the image horizontal to the laptop screen (confirmed by using the crop tool), so there was a 12 degree rotation.

There is no way a 12 degree rotation can be an orthonagonality issue with my mount/scope alignment - well I seriously hope not...!!!

If I had a +/- 1 degree rotation then I could live with that, but not 12 degrees, so I'm sure hoping that I never see this again...

Thanks everyone for your feedback.

Best regards,

Geof

[Starlight 1]

Did you look in the help? With SGP after the flip it will take a photo and tell you how far the camera is out , so you can ajust it before it start taking the new data.

[geoflewis]

12 minutes ago, Starlight 1 said:

Did you look in the help? With SGP after the flip it will take a photo and tell you how far the camera is out , so you can ajust it before it start taking the new data.

Hi Starlight 1,

I did look, but did not find it. Please could you let me know which section(s) of SGP help I need to review. BTW I did not use SGP's meridian flip tool as being a new SGP user I've yet to work out how to set that up. I just stopped the squence then restarted it so that SGP moved the mount to the 'correct' side of the pier. Ths was not a pause and resume, I actually aborted the sequence then unchecked the RGB events so that it started over at the L event on run sequence. As you can probably tell, I'm still muddling through the correct operating procedures.... .

All help gratefully received....

Regards, Geof

[Starlight 1]

PAGE 68/70

[geoflewis]

4 minutes ago, Starlight 1 said:

PAGE 68/70

Thanks, but I don't see any page numbers in the help section, so I've no idea how to get there. What topic heading is it? Where in Norfolk are you, could I phone you perhaps, if we exchanged phone numbers by PM? Cheers, Geof

[Starlight 1]

http://www.mainsequencesoftware.com/content/Sequence Generator Pro.pdf do this link work. it may be on page 96  

[geoflewis]

9 minutes ago, Starlight 1 said:

http://www.mainsequencesoftware.com/content/Sequence Generator Pro.pdf do this link work.

Thanks, I have downloaded and will check it out. I was searching the help notes within the application. From an initial read I see this requires a rotator to be set up and connected, which I don't have, but I also see reference to a manual rotator so is an actual rotator required, or can I just rotate the camera using the rotatable flange on the Moonlite focuser? Cheers, Geof

[Starlight 1]

After the flip it use Plate -Sol so you have be on the inter-net for it to work and tell you how far the camera out in manual rotator  . just check links in pagers as well As I may have seen it in one of the link.

[geoflewis]

1 minute ago, Starlight 1 said:

After the flip it use Plate -Sol so you have be on the inter-net for it to work and tell you how far the camera out in manual rotator  . just check links in pagers as well As I may have seen it in one of the link.

I used PS2 with ANSVR (local astrometry.net) as blind solver, to get on target after the flip.

I need to read / understand more about the rotator option to get the rotation error reported as so far as I know the existing plate solve is not reporting that and once the target is centered it resumes the capture sequence without me having any opportunity to adjust the camera orientation.

Like I said though, I'm completely new to SGP so its all part of the learning curve, so thanks for the pointers. Hopefully my issue was a one off mechanical one that I won't see again.

Many thanks, Geof

[Starlight 1]

let call it plate sol live , it look at the last sub before the flip and take a new one after the flip and tell you how far to move your camera left or right and then it take one more sub and check you have move by the right amount.

[geoflewis]

14 minutes ago, Starlight 1 said:

let call it plate sol live , it look at the last sub before the flip and take a new one after the flip and tell you how far to move your camera left or right and then it take one more sub and check you have move by the right amount.

Sounds great, I'll see if I can get that functionality working. Many thanks, Geof

[Starlight 1]

Its no good me trying tell you how to set it up ,I come by this way after my rotator pack up and trying to work it out with a protractor and reading a post on here about rotators on domes. 

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[geoflewis]

2 minutes ago, Starlight 1 said:

Its no good me trying tell you how to set it up ,I come by this way after my rotator pack up and trying to work it out with a protractor and reading a post on here about rotators on domes.

No worries, I'll work through the help pages and manual rotator set up notes. Something to test when the sky isn't up to serious imaging maybe....