Lunar mosaicing, how to?

[ONIKKINEN]

Nights are getting shorter here and i am desperate to try and do any kind of shooting while i still can but with the Moon in the way i am discouraged to try and get some sub par data for any of my running projects, so why not shoot the Moon? It will be low in the sky and my setup is hardly ideal for this but whatever a shot is a shot and ill take it.

I have an 8'' F4.4 newtonian and an ASI120MM that ill put in a barlow for this, but the question is: How to really shoot or plan the mosaic? Is there some software that can have a Lunar mosaic sequence saved in or is this usually just done eyeballed and manually slewed? I can of course just manually slew and eyeball the framing but would be convenient to have some kind of auto sequence to deal with the way too many panels that i would need to fill the entire Moon with. I am planning to take the shots with sharpcap as thats what im familiar with, but i have actually never used the 120MM for anything but guiding so far. I may take RGB with my risingcam through my coma corrector (at F4.2) to make a composite, but well see how the mosaicing goes first.

[ollypenrice]

Not really my thing but my few forays into lunar mosaics were done by eyeballing (like my many deep sky mosaics) and combined simply in Microsoft ICE. I couldn't fault it on the moon, though I wouldn't use it for deep sky.

Olly

[vlaiv]

I usually eyeball it - but it is very simple procedure to do - not really eyeballing in common sense of the word.

Follow certain pattern - like left to right until you reach the end then "step down" and reverse direction for next row (do it row by row like that - each time stepping down and doing a row).

- Make sure your FOV is aligned in RA/DEC direction

- When moving single FOV - think about which direction you are moving in and then simply look at a feature in live view and position that feature on opposite side of FOV - simple as that.

For example - moving to the right would be like this:

Note feature that I outlined at the right side of FOV - slew so that it is positioned on left side of the FOV:

Always use feature that is roughly the same size - this will be your overlap zone for easy joining of the panels. When moving up/down - choose feature on appropriate edge (for moving down - use bottom edge and place one of features that is there - on top of subsequent FOV).

 

[ONIKKINEN]

3 hours ago, ONIKKINEN said:

an ASI120MM that ill put in a barlow for this,

Actually scratch that, my Rising Cam has much higher framerates than the USB2.0 120MM mini with a reasonably sized ROI so i will be using that. Halved the amount of panels needed! That is if coma doesn't start to become an issue with a larger sensor but i think something like a 1600x1600 capture would still be ok-ish, maybe, hopefully (just guessing).

[vlaiv]

53 minutes ago, ONIKKINEN said:

Actually scratch that, my Rising Cam has much higher framerates than the USB2.0 120MM mini with a reasonably sized ROI so i will be using that. Halved the amount of panels needed! That is if coma doesn't start to become an issue with a larger sensor but i think something like a 1600x1600 capture would still be ok-ish, maybe, hopefully (just guessing).

Radius of coma free field is F^3/90 in mm

If you have F/4.4 telescope - then coma free field is ~0.9465mm (radius or about 1.893mm diameter).

That scope is rather fast and you really want to use barlow lens with it.

Critical sampling will be at about F/ratio = pixel_size * 4 (that is for 500nm wavelength - good value to use for full spectrum sampling).

You want to be at ~F/15 so you'll need at least x3 barlow if you want to go for critical sampling.

In any case - diameter of coma free field will be enlarged by barlow factor. x2 barlow will make it ~3.8mm. That is ~700x700 ROI with 3.8um pixel camera.

With x3 barlow - you'll be able to do ~1024x1024 ROI.

 

[ONIKKINEN]

2 hours ago, vlaiv said:

Radius of coma free field is F^3/90 in mm

If you have F/4.4 telescope - then coma free field is ~0.9465mm (radius or about 1.893mm diameter).

That scope is rather fast and you really want to use barlow lens with it.

Critical sampling will be at about F/ratio = pixel_size * 4 (that is for 500nm wavelength - good value to use for full spectrum sampling).

You want to be at ~F/15 so you'll need at least x3 barlow if you want to go for critical sampling.

In any case - diameter of coma free field will be enlarged by barlow factor. x2 barlow will make it ~3.8mm. That is ~700x700 ROI with 3.8um pixel camera.

With x3 barlow - you'll be able to do ~1024x1024 ROI.

 

Ah my back of the napkin calculations where nowhere near correct then. Well i ended up using the 120MM since its mono and simpler to deal with. Not sure what strength of barlow i ended up with since i played around with the sensor to barlow distance but i think the 120MM is mostly free of noticeable coma, although seeing was not great and i doubt there will be a pretty picture in the end.

[ONIKKINEN]

Missed some of it...

Ill try some trickery with some previous data to see if it can be turned into a full image. Probably not great but ill see it through.

[ONIKKINEN]

Actually, turned out half decent and maybe even presentable with a half-moon crop:

All the detail is in the terminator side anyway, so ill call this a planned end result. Not sure if the seeing supported the resolution here, but its not awful at least.