Imaging Over Two Nights

[Graeme1858]

Hello, I have captured some subs of M81/82 for the June astrophoto challenge but around the summer solstice and on a school night the time available is only an hour or so. It's clear again tonight so I contemplated going out again for some more subs. Not having tried a two successive night session before, I was wondering how to ensure the camera is aligned in the telescope in exactly the same orientation?

I composed the light frame images last time using the lucky coincidence of M81 and M82 being on the same declination. I know the coordinates of the target so I can get the centre of the target in the centre of the frame. I can take a single image and send it to Stellarium which will show how the camera is orientated and I can then rotate the camera to get it about right. But then is that close enough for DSS to sort it out and accurately stack the frames from both nights or is there a trick I need to know about?

Regards

Graeme

[OhNo]

What are you using to capture your images? Some (meaning "not all") capture programs have a Plate Solving area integrated into them. Declination shouldn't matter., unless your doing short exposure on a Alt/Az mount, but I see you have a CGX listed in your signature.

I use a couple programs for capture. Sequence Generator Pro and APT both have the ability to reproduce framing on different nights. I'm sure there are others that will perform the task as well.

[starfield]

Graeme,

I've used a process similar to what you described before I started Plate Solving. If your center point or rotation is off, it's going to make your borders "rattier" and means you need to crop more to get the portion of the two stacks where everything is lined up. Not sure how much wiggle room you've got based on the framing but give it a whirl. One other thing I'd recommend is putting the second group of subs in a separate group tab in DSS with it's own flat.

Good Luck

--Steve

[Graeme1858]

What are you using to capture your images? Some (meaning "not all") capture programs have a Plate Solving area integrated into them.

I'm using APT for capturing. I can plate solve an image and the excellent APT Goto++ function gets to the centre of the target but the camera rotation is down to however it's put into the telescope. I only told half the story though! I've captured some frames on M81 and I've added a few minutes of RA (same Dec) to capture more frames of M81 on the edge of the frame in order to stitch the two in ICE to create an image of both M81 and M82 for the June AP challenge.

Because I only captured 10 x 240 seconds of each I was contemplating getting some more data on a subsequent night.

So, I wondered how you people that are imaging over multiple nights are able to ensure that the camera is aligned accurately between sessions? Or can DSS sort it out?

I've used a process similar to what you described before I started Plate Solving. If your center point or rotation is off, it's going to make your borders "rattier" and means you need to crop more to get the portion of the two stacks where everything is lined up. Not sure how much wiggle room you've got based on the framing but give it a whirl. One other thing I'd recommend is putting the second group of subs in a separate group tab in DSS with it's own flat.

I'm confident the camera is roughly orientated correctly because I placed the edge of the frame parallel to the RA line in Stellarium. But only by eye, so I wondered how accurate it has to be for DSS to be able to handle it and if there was a secret APer trick that proper APers know about that I still have yet to learn.

Separate calibration frames was something I had considered but DSS group tabs is something that is new to me. I'll have to read up about it. Thanks.

As it goes, I was out last night but the CPWI software was unable to see the mount. Nightmare. The HC is quite new because the original one packed up. I'm getting various error messages. I hope it's not a problem with the mount! The telescope fell to bits a few months before the HC packed up. I need to fix the problem, there's a new camera in my birthday box!

Regards

Graeme

[OhNo]

Ah, now I understand better. There are a couple things I have done in your situation. Number one: I only ever take my camera out of the scope to collminate the scope. Two: I note a reference point on the scope and camera.

A minor rotation of the camera isn't a big deal breaker for DSS. Rotating to add to the edge of the data could necessitate doing a mosaic. Lots of people tend to forget one thing about a GEM mount, if your imaging and doing a meridian flip the image ends up inverted to your chip, DSS still stacks it, right!