How to make a mosaic image ?

[Stellaris]

I use a SW 150P explorer with a SW NEQ3-2 Pro Goto.

Simply put, I have no idea how to make a mosaic image. I don't even know what software to use to set it up or to control my rig.
So I guess my questions can be summed up to: What and How?

[Elp]

Is your setup already automated (auto guiding, auto goto/computer controlled)?

I use the telescopius website to plan my mosaics, then copy the CSV data into my asiair, et voila all the panels are imported into the plan.

I assume other astro software like NINA work the same. If your setup is fully computer controlled, and polar aligned, the software will auto slew to each mosaic panel, take an image, plate solve, decide if the scope is centered, take the specified number of images then auto slew to the next panel etc. But usually I only do one or two panels at a time, as total image duration per panel still applies to get a good image.

Edited August 22, 2023 by Elp

[tomato]

You can use software to plan your mosaic and then let it do all the clever stuff all on its own, but if you are not there yet you can start off in pure manual mode.  Pick an object that needs a couple of panels to cover it, e.g. my first mosaic was a two panel image of the Eastern Veil Nebula. Align your field of view for the first panel, then once you have those subs move the FOV so around 10-20% of the first image is still visible either along the top or side edge then take your second panel. I’m not sure what free software will align the two images post calibration but I use APP which makes combining the panels really straightforward and creates a seamless join to boot.

[Fegato]

I use NINA for acquisition - it's free, and among many other things, it will frame a mosaic for you. And then it can plate solve (via ASTAP) in order to get precise positioning. I'd recommend it.

For mosaic production (and everything else post acquisition), I use Pixinsight - obviously that costs money and has a learning curve, so may or may not be for you.

[Stellaris]

My rig has a go to mount, however my scope is manually focused each time. That’s as automated as it is.

What’s plate solving ?

[Elp]

Plate solving: an input image is taken or entered to be analysed, and cross referenced with an existing star database, then sky location, coordinates, and any identified objects can be identified within the input. It's an invaluable tool when framing, even more so when doing mosaics.

If your mount is goto, all you have to do is start by having your target centred, then move in Ra or Dec slightly to increase to the next "panel". Keep a log of the coordinates in the handset so you can repeat in another session.

If you use the telescopius website as I advised, you can use the Ra and Dec coordinates it provides to input into your hand controller. The only thing you'd have to recheck is your camera/scope rotation matches your previous data if you're doing the imaging over multiple sessions to maximise the final usable imaging area as the borders will need cropping to a rectangular or square final size if you care to finish and present the image.

Edited August 24, 2023 by Elp

[Fegato]

Well, I guess one step at a time, but if you are keen on astrophotography, automation sort of becomes inevitable...   plate-solving is where software uses the stars to precisely point your scope at a particular position / target.  A pre-requisite is that you have your mount attached to a computer (Windows is pretty much standard, as some components only work on Windows) - there'll be explanations of how to do this in your mount documentation and/or elsewhere on the net if you want to go down that route.

 

[DaveHKent]

It depends on what you are imaging. I have only ever done a mosaic for lunar imaging and I do that manually, though I'm aware there are tools that can help.

Once I have stacked the videos and got my final stills, I use GIMP

• Create a new image and make it large enough to fit all the stills. I often default it to a bright green background, rather than black so I can really see where I have put things
• Open all the other images as layers, either as a bulk operation or pull one in at a time as needed.
• If you open all of them, make sure the Layers tool box is open and use the eye icon to make them all invisible
  • You may wish to name your layers at this stage if that will be helpful
• Make the first layer visible and position it to roughly where you think it should go in your final image
  • Lock the layer in place
  • Hit save! Hit save again and keep saving after every operation.
• Now make the next layer visible. This should be one that overlaps a little with the first.
  • Drag the opacity slider down to about 50%
  • Use the move tool to position the second layer over the first. With the lower opacity you should be able to align far easier, placing craters directly over the same crater from the previous layer
  • Once you are happy, drag the opacity back to 100% and you should have a neatly aligned image
  • Optional: Sometimes you can get a visible but not too obvious line where they join, due to slight colour variations. On the second layer select the erase tool with a fairly wide and medium hardness airbrush. Go down the joining edge and remove some of the image to give a softer edge
• Repeat for the other layers.
• Crop the final image to remove the green around the borders, or if you do need to fill in border gaps, use the colour dropper tool to select the background sky from the image and flood fill that colour. If you pick black (#00000) from the colour pallet you will find the sky you captured was less black than you thought. (Fans of Father Ted, think priest socks)
• Once complete, you can leave it as it is or merge all the layers down. When you export into another image format it will merge the layers down anyway, so I usually leave all the layers in my GIMP .xcf file in case I want to go back to it later.

Depending on your equipment, you might also have to rotate some images. I have an altz mount, so if I'm imaging an almost full moon, for me that is 9 images and the final shots can be rotated in relation to the first by a couple of degrees, depending on how long the imaging session took.

 

[WolfieGlos]

On 22/08/2023 at 19:51, tomato said:

I’m not sure what free software will align the two images post calibration but I use APP which makes combining the panels really straightforward and creates a seamless join to boot.

As for free software, ASTAP does it, I’ve used it twice so far and it was quite easy just following the help file. Granted they were only 2x1 mosaics and they were manually framed in NINA, but it worked. Both posted on SGL somewhere, the NA/Pelican and Lagoon/Trifid nebulae. 

[900SL]

On 22/08/2023 at 19:50, Stellaris said:

I use a SW 150P explorer with a SW NEQ3-2 Pro Goto.

Simply put, I have no idea how to make a mosaic image. I don't even know what software to use to set it up or to control my rig.
So I guess my questions can be summed up to: What and How?

Have you tried typing 'astrophotography mosaics' into Google and spending some time looking at relevant youtube guides etc?

[ollypenrice]

Plate solving is great when and if you have it but even a 35 panel can be done by hand, this one by Tom O'Donghue and myself.

http://megamosaic.astrophotography.ie/mosaics_page.htm

AstroPixelProcessor is the software of choice, at the moment, for constructing mosaics. It is important to use good flats per panel and also to gradient-remove each panel first.

Olly