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Old 21-10-2014, 07:53 AM
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Creating a mosaic with TSX and PixInsight.

I've wanting to start my first mosaic this summer. the target I'm choosing is Orion's belt and sword.
I have TSX set up with the mosaic grid set up and framed for my image scale and rotation and I can import that target list to CCDAP5 no problems. I hit go the other night but had some guiding problems but by the looks of things everything imported ok and was working well for image acquisition.

The question I have is about strategy. what is the best way to go about it in your experience?
How many subs per panel would you normally take. I know this would be dependent on the target. But I was thinking that as a mosaic would be pretty high resolution the noise should be buried in the signal pretty well.

Also do I take say 10 images of each panel then move on to the next or take one image each panel and start again. I think I know the answer to this one but worth asking just in case.

Also I dont see how to to stack and align them in PixInsight. Any tips on how to achieve this would be great.

I'll get to processing once I've figured out all of the above.

Thanks
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Old 21-10-2014, 08:20 AM
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RickS (Rick)
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You can get away with less data per panel if you're going to downsample the final mosaic. This is effectively software binning. Apart from that the individual panels are no different to any other image wrt the amount of time you need to spend on them.

I'd recommend that you do at least one sub of every panel and make sure the mosaic is going to fit together before you spend too much time on it. I share a scope at SRO and we've had problems with a couple of mosaics planned with TSX where we didn't check the fit until the end (and had to reshoot a couple of panels.) We're still trying to figure out what the problem was. It has been claimed (on an Internet forum, so it must be true!) that TSX doesn't account for the curvature of the sky but it could just be that we didn't match PA correctly between plan and execution.

Spreading your imaging time each night across several panels might help a little with matching them to each other but I don't have a strong preference between doing it that way or doing complete panels one at a time.

Cheers,
Rick.
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Old 21-10-2014, 09:32 AM
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Octane (Humayun)
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I've had curvature issues with TheSky6 mosaics. It's almost like as if each panel needs 1-2 degrees of rotation to fit.

Rick's right; make a scaffold mosaic first -- that is, take a 30-second exposure of each (I use a 10-20% overlap -- to help account for the curvature issue) and then join them together to see if it's going to work.

Joining mosaics is a time-consuming task.

I can write a detailed reply once I get home tonight on how to do it.

H
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Old 21-10-2014, 09:37 AM
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Cheers guys appreciate it.
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Old 21-10-2014, 10:11 AM
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25% is a good amount.
You can do it manually its just as easy. I used the mosaic tool on my last mosaic (yet to be processed - warning they are time consuming).
But I went for 20-25% overlap as you want plenty for good stitching points. Too little and there are not enough stitching points for a good combine.

The main advantage of the Sky X tool is speed. You click on the panel and it go-tos the centre of the panel. Nice and fast but you would still be wise to double check it by using the focus image against your last panel's luminance image (reduce it so its the same size) and manually line it up if necessary.

Automation is good but it does not replace your need to control things.

With mosaics its best to image the same time of night for each panel, the same exposure lengths, the focus is critical so make sure its spot on for each panel (one panel with poor focus stands out). Usually the problem with mosaics is the background's are different, hence the previous statement. Overlap 25%, about 2.5 hours per panel, under the same circumstances. You'll find that is hard by itself as one night is clear the next may have high thin cloud causing halos, or wind causing guide errors. You end up with some incomplete panels that need to be imaged to complete them on a different night. So keep good admin, do a manual drawing where each panel goes (some panels in a multi mosaic can be undistinctive and hard to work out were they go so number them like Sky X does and save them that way).

Best to do a 2 panel one and see how you go. If successful do a 4 panel one. I wouldn't try an 6 or 8 panel one to start.

I notice Rogelio often uses 2x2 binning to reduce exposure times at the expense of resolution but when viewed at regular sizes the resolution is fine because its such a wide field of view. He goes 1.5 hours per panel which is low but then he'll do a 16 panel mosaic and he uses Pix Insight which is a difficult program to use.

Greg.
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Old 23-10-2014, 11:56 AM
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Thanks for the info Greg. I think TSX only has 5% overlap as standard so I'll change that when I gets some decent weather.

Sandy.
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