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seventyf

Imaging over many sessions

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I'm using a 200P and 60D and have some questions about alignment and rotation, I'm struggling to get to grips with this and it means that I can only use data from one session for my images

How do you make sure the images you take in different imaging session align so you can stack them, especially rotation?

Also how do you align you camera so the resulting image is the right way up, i.e. north at the top of the frame?

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I have been looking into this as I have to break my kit down each evening. Deep Sky Stacker is fairly resilient to some movement but extreme differences as you probably have found out mean the results are not usable.

Either keep all of you imaging kit attached and don't move it! Maybe some sort of non permanent marking of some sort? None of these are practical for me so I have been looking at Plate Solving.

Various programs such as Astro Tortilla, SGP and Astro Art offer the ability to take an image or use an image from a previous session (or even someone else's from the Internet!) .

When Plate solving the software will identify the co-ordinates and allow you to slew to it lcoation. That makes it sound easy but it can a bit of a challenge to configure the software and data libraries applicable to your scopes FOV etc. So patience is needed, at least I had a lot of issues to start with.

Whilst the initial plate solving is ok. I need to be able to then synch the plate solve with even more accuracy or else the images are still not an identical fit.. This is proving a challenge but I am close to finding a solution...

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It's a good question for the UK weather - I rarely achieve a satisfactory set of images from a single evening, and more typically need at least three evenings.  And I have to put everything away at the end of each session.  

I'm not sure about a DSLR, but I use Astrotortilla, which it's true, does take some setting up, but is well worth the investment of time.  This puts the centre of the new image within less than one minute of arc of the centre of a previous image.  

For rotation, and this applies to any camera, I judge the position of the camera against the scope by eye, and find it easy to get within one degree - I try to always use the same position, e.g. side of the camera label in line with the finder scope. 

Having the image "the right way up" is irrelevant because anyway it will be inverted after any meridian flip, and you will not lose image area.  Most stacking software is able to rotate images through any angle.  

Chris

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I've never had a set of images that wouldn't stack because of rotation between sessions/after a meridian flip. I've had plenty of other issues, but that's not for here...

I generally align the camera east-west or north-south and can usually do so by eye to within a couple of degrees, which results in acceptable cropped pixel loss. I worked just as hard to pay for the pixels at the edge of the frame as for the ones in the middle and, by golly, I'm going to get my money's worth! ;)

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I use the 200pds too and I know what you mean, you dont get much leg room to crop at all. Ive had this problem a bit recently too as ive been imaging over multiple nights. 

I use a Mac (although hopefully soon to be PC) for my guiding etc so astrotortilla is not an option for me.. So far ive just picked out the bright stars in the live view image then viewed the last image from my previous session and flick back and forth doing my best to align the stars so they dont jump when swapping from image to live view.

However ive got a 81mm frac on order so this will hopefully be a problem of the past for me soon! 

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I used to have the same issue, but plate solving definitely seems to be the best way for me now. Also, probably best not to remove or change the camera if possible in order to keep the same angle when setting up on another night.

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When I used to use my G11 for imaging then yes, plate solving was the way to go. SGPro offers all the tools you need to get back on target the next night including a 'manual' rotator which basically tells you which way to turn the camera and by how much, you do what it advises (i.e., a guess on your part!) and then check with another plate solve if it's back in position.

ChrisH

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For quite some time now I have been using the software package "RegiStar" for this purpose as I tend to mix and blend images from different focal length scopes using different cameras with differing pixel sizes and aspect ratios etc.

RegiStar is a one-function package, it seems rather expensive as it does not do anything else except align wildly differing images perfectly for stacking, even correcting for field curvature, but what it does it does brilliantly.

A non-time limited trial is available you just can not save your final image without buying a license.

https://aurigaimaging.com

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For quite some time now I have been using the software package "RegiStar" for this purpose as I tend to mix and blend images from different focal length scopes using different cameras with differing pixel sizes and aspect ratios etc.

RegiStar is a one-function package, it seems rather expensive as it does not do anything else except align wildly differing images perfectly for stacking, even correcting for field curvature, but what it does it does brilliantly.

A non-time limited trial is available you just can not save your final image without buying a license.

https://aurigaimaging.com

A one trick pony but what a trick! It's fabulous.

Regarding rotation, surely it's easier always to align along RA and Dec in either portrait or landscape to save time in the future. I rarely feel the need to deviate from this. Like cfpendock I do this initially by eye but then I go to the camera and take a 5 sec sub while slewing very slowly. This produces a star trail which shows the current camera angle clearly. You just repeat this, rotating the camera slightly each time, till the trails are horizontal or vertical.

If I have to take off one of the cameras on our carefully aligned dual rig I'll set the CW shaft to horizontal with a spirit level and the OTAs ditto. I'll then stick a bit of masking tape on the back of the camera, hold the spirit level up against the tape and draw a line once the level has been set to horizontal. When I put the camera back on I just hold the level to the line and rotate the camera to level again. This doesn't take long and saves time when time's precious - at night.

Rotating to a random angle rather than to RA and Dec takes absolutely ages so, for me, random angles are a no-no.

Olly

Edit. If you are not using a camera with filterwheel you can use a blob of Tippex spanning the camera and the focuser to recover an exact angle. If you have to separate a FW from the camera then this won't work.

Edited by ollypenrice
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I've two nights of Horsehead data to stack.

If I stack all the lights without darks and flats, I've found DSS isn't bothered by the slight rotation between nights.

But if I stack each night separately with their matching flats and darks, the resulting two images can't be stacked - they are different sizes (4271 x 2844 and 3986 x 2797) and are slightly different "zoom" too, and DSS objects.

Is there any way to match lights to flats for each night in the same stack?

Michael

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I find the 'Framing Mask' feature in APT software very useful for getting the camera rotation close between imaging runs.

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Michael re different size images out of DSS check what you have set the output to, it can be one of three, everything, fully overlapped or original size based on start image. For multiple sessions you need the last one. The others will give different sizes over different sessions.

Rob

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I find the 'Framing Mask' feature in APT software very useful for getting the camera rotation close between imaging runs.

+1 for plate solving or APT ... 2 different approach that can be used depending on your needs.

I'd like to point out that there is a similar feature in BYEOS that lets you overlay an image from a previous session over one snapped on your DSLR, then you can adjust transparency and adjust the 2 images to frame them.

Edited by Vox45

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Quote:    

"Michael re different size images out of DSS check what you have set the output to, it can be one of three, everything, fully overlapped or original size based on start image. For multiple sessions you need the last one. The others will give different sizes over different sessions. 
Rob"

Many thanks Rob, I see now how that would help.

Michael

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Hello.

Sorry to dig up an old thread.

 

Droogie 2001.  did you ever get AA5 to plate solve and sync your mount ?    I had hoped there would be a method without using scripts, I got the impression you were getting to the bottom of the puzzle.    If you have what is your method?

 

cheers

Mark

 

 

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I have just been looking through my notes. I did have some success but the main issue I had with AA was the frame and focus. It was very difficult for me to align the stars for star alignment, I seem to remember the frame alignment windows were tiny?

So I went over to SGP and never looked back.  Since then I realise I may have been making things difficult for myself in the first place in that I may not have had to do a manual alignment, just solve and synch.
Again SGP has helped with this so as I have committed to that software I did not go back to Astro Art.

The Astro Art Forum was very helpful

http://www.astroartforum.net/forum/

(posted wrong link first time...)

If you can get Plate solving working on AA it is very fast and accurate.

 

 

 

 

Edited by Droogie 2001
Wrong link

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Hello Mike, thanks for your reply.

All I want is to do is take an image , AA plate solves, I sync the RA+ Dec centre co ordinates and off I go, im not too worried about plate solving an older image and perfect re-alignment.   Were you using CDC do you recall, when you Sync in AA did it update the position in CDC ?

Ive had a look at SGP before , nice features but I got the impression you need to be online to use plate solve ? 

Regards

Mark

 

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Hi Mark,

I honestly cannot recall and I have since removed the trial software from my PC. Not much help on that, sorry. :sad2:

However you can setup offline plate solving on SGP. In fact this is what I use with my SGP.

This link may help get you started. If not check I am sure there are other Forum thread on the SGP Forum about this common requirement.

http://forum.mainsequencesoftware.com/t/astrometry-net-local-solver/584

Basically you amend SGP so that it looks locally on the HDD, its not that difficult to setup.

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