200mm LMC

[SimmoW]

while the MyT mount is being repaired (Software Bisque have kindly offered to swap the main board), I am bedding down my latest setup, the ASI1600 and filter wheel with the 200mm lens. Very happy with these early results, although guiding needs to be improved due to terrible Dec balance of the guidescope side by side setup. Soon to be fixed with use of the oag.

Also focus changes considerably between blue and Ha and the other filters, so an arduino elec focus conversion is in the works.

Not a bad FoV eh?

Best version (https://www.astrobin.com/full/347560/)

[skysurfer]

Probably strong Halpha filter ?
Nice picture.

I once did it with the Canon 200 2.8L and the 6D + UHC filter and showed the red nebulas, but that did not come near to this.

[SimmoW]

Haha, only a 3nm ha filter.

[Atmos]

You've picked up some really nice detail Simon but the Ha has overpowered everything more so than complementing it :) You're using PixInsight?

What I do is use LinearFit on all of the subs when then allows PixelMath to be used to create the image. I have found that using the Red channel as the reference works best. What this will do is make the Ha, L, G and B frames so that they are at the same intensity as the R channel.

Then in PixelMath I use:
R: Max(R,Ha)
G: G
B: B

This will create a RGB image that is almost colour correct but you will need to change the black point.
Because the Ha and L frames have been fitted against the R frame, you can use:
Max(Ha, L)

This will create a new master luminance with the added Ha but it won't be too overpowering.

[SimmoW]

Thanks so much Colin, am definitely trying to experiment with the best way to combine so I'll give your ideas a try. I've been doing a lot of combining in Photoshop but it is very labour intensive

[Placidus]

The H-alpha is what makes the image seriously special. I wouldn't reduce its impact (as opposed to colour balance) very much at all.

The zero point for the image is too high by about 6500 counts out of 16 bits, making everything washed out.

The broad process should be to prepare an H-alpha image that is publication ready, then separately an LRGB image that is publication ready. The LMC will have a great abundance of very bright blue stars. Then combine the two images. The R = Max(R, Ha) is one approach (in PhotoShop layers, use LIGHGTEN blending mode with opacity of 100%.). Another almost opposite approach is R = (R + Ha)/2. In PhotoShop that's NORMAL blending mode, with an opacity of 50%, though you can use any opacity you like. Use each separately produce the nicest image. Then blend the two approaches to produce the nicest compromise.

(I use GoodLook, not PhotoShop).

Once again, an excellent image, especially if viewed as a whole. Its strength and importance is in the depth of the H-alpha.

Very best,
Mike

[RickS]

https://www.youtube.com/watch?v=vKj4upY1VYI

Nice image, Simon.

[SimmoW]

Haha thanks Rick, I think! One of my most fave bands as well.

So here is a quick revision, what ya think? I used Colin's suggestion to linearfit the Ha to red, can't believe I didn't do that! Seems to have toned things down more. But I have lost some of the fainter tendrils. Not really an issue with this test shot as I had pretty low ha data so the fainter stuff is enmeshed with noise.also use that new photometric colour calibration tool to improve the colours Mike n Trish.

Oh I use the NBRgb script in PI to combine the images, too lazy to use pixelmath. Seems to work very well. Pity that great SHO-AIP script is no longer supported!

[Paul Haese]

That's a nice shot of this weirdly shaped galaxy. I like the composition, it seems to fit quite well.

[Placidus]

Hi, Simon,

To us that is much better than the original. There's still considerable room to make the blacks less milky, and to give more emphasis to the stars without touching the red. In the attached, all I've done is to adjust the black point, increase the blue rather a lot, and increase the green a half smidgin. I've not touched the red. Of course working off a 200KB image means it won't do your underlying image much justice but it gives the idea.

Once again, you've captured a fantastic wide field record of the structure of the LMC.

Very best,
Mike

[SimmoW]

Thanks M&T for spending the time, I must have a preference for lighter backgrounds. I will examine the histo when I can, to compare to my last revision.

I normalised the colour via the PI colour calibration tool that uses plate solving, I noticed my star colours were a lot bluer.

Thanks Paul, yes it's a rather deformed thing eh. So full of interesting formations though

[Placidus]

We promise to stop nagging. :D

[SimmoW]

Don't stop, I often use your nagging to remind me at the end of the processing to check my levels!