M81 Bode's Galaxy + Holmberg IX (10 hours of data)

[Menno555]

M81 Bode's Galaxy including Holmberg IX (faint smal area at the top in the middle), a mag 16.5 dwarf irregular galaxy. It's very young with 200 million years and is the youngest nearby galaxy.

My first capture with more integration time, in this case 10 hours

There were finally a few clear nights but (of course) full moon on top of my Bortle 7/8 sky. So decided on the fairly bright M81.
The first set was with the Optolong L-Pro filter but there was SO much red in it.
So decided for the more neutral Baader Neodymium Skyglow filter in the next set.
This helped but still not that much blue. But by now I understand that that is way better shown with a mono camera with color filters.

All in all a good result (I think). And again amazed by the Ioptron CEM25EC mount: for the Optolong set I did 411 second exposures with tracking only.
The 2400px version with more details visible can be viewed here: https://i.ibb.co/Hg3TX4Y/M81.jpg

Bortle 7/8
Meade LX200 8" f/10 ACF OTA
Ioptron CEM25EC mount (no guiding)
Baader Neodymium Skyglow filter
Optolong L-Pro filter
Zwo ASI071MC Pro camera

Captured with SharpCap Pro @ -10 Celsius
Optolong L-Pro: 38 x 411 sec / Gain 10 / Offset 4 / White balance R60 B99
Baader Skyglow: 85 x 240 sec / Gain 0 / Offset 4 / White balance R50 B50
For each set set: 40 x Darks / 100 x Flats @ 3 sec 25500 ADU / 100 x DarkFlats

Stacked in DeepSkyStacker
Stacked the Baader and Optolong set and also stacked the 2 resulting stacks, so 3 stacks in total

Processing for several hours in Siril and Photoshop
Siril: processed the 3 stacks separately. Photometric color calibration, Background Extraction and Histogram
Photoshop: placed the 3 images on top of each other and then several steps which I forgot: it really was trail and error with it all. It included levels, curves, brightness/contrast, color balance, some noise reduction with Neat Image Reduce Noise, crop.

[timh]

Hi Menno,

I am guessing that the 071MC is your replacement camera for the ASI294? The specs look good. Anyway nice sharp image again even with nearly 7 minute unguided lights which certainly attests to the quality of that CEM mount - and even more so since a 200 mm scope must be near the top of its weight range?

One of the reasons that I like this Gallery (thank you Robin) is that it is such a good opportunity to compare different equipment set ups and the various tips and tricks that folk use and to see what they do in practice.

On galaxies, nothing in my limited filter box (UHC-E, UHC) has seemed to help at all (although never tried the Neodymium) and my best images by quite a margin were all obtained under fortuitously dark skies whilst on holiday (Bortle 4). Nevertheless I have been imaging galaxies under the usual Bortle 6 skies but only during those short windows of opportunity with clear skies and no moon. Thus opportunistically collecting RGB lights for an hour or using the fastest optics configuration and the OSC camera.

So, naturally, I compared one of my M81 images (120 min RGB blended with about 50min of lum and HA all at F4.5) with the image you posted. Your 10 h capture time has clearly helped but I suspect that with Bortle 7/8 skies the gods are against your capturing much more of the faint detail than you have? At Bortle 6, my images have gone slightly deeper and thus show more extension to the spiral arms and a clearer view of Holmberg IX (thanks for naming it - I had yet to do the research to find out what it is ) although I always get the impression that your images are just that bit sharper (maybe to do with being at F10?). I find galaxies and galaxy fields some of the most fascinating astronomy objects but the dark sky opportunities to really image them as I would like to all too rare.

Tim

[Menno555]

Hi Tim

Yep, the 071 is the replacement for the 294. And the weight of my 2032mm scope is really not that much: I am at a total now of around 6.4 kg and the maximum payload of the mount is 12 kg, so well within that.

And yes, those very faint things are limited here by the Bortle 7/8. Plus the full moon in the sky. And being f/10 it is just harder to capture the larger faint structures. Plus I did not capture in real Ha (yet). But also, I am still learning all kind of things: it's quite possible that this will work better with more and shorter exposures, lets say 150 x 180 seconds with Gain 20. But in this case I did use the Smart Histogram solution for the 411 sec exposures and my own "gut feeling" with the 240 sec ones.

As far as I know f/10 will produce "larger" stars giving the impression that it is less "sharp" (the bloated stars) then with for example an f/8.
With the 071 I did notice though that a lower gain really helps to make that less bloated and give a sharper effect. That plus the excellent optics of the scope and checking my focus every hour or so with a Bahtinov mask and the free Bahtinov Grabber software I did try the SharpCap focusing assistants but that's not for me.

And the gallery here is indeed cool. Of course for showing off our work but also like you said for tips and comparison.

Menno

[timh]

Hi Menno,

Thanks. I didn't even notice that it was done under full moonlight - very good picture then - maybe those filters did help a bit?

Clearly you are right that F10 will inherently produce a bigger image and each star occupy more pixels.... thinking it through though - relative to the size of the image itself - will stars just scale to look the same realtive size ? Not sure. A lot of the apparent star size is probably more to do with brightness spread and image stretching etc.. not really sure ...

I have a real problem with getting good consistent focus probably partly because the sweet spot is inherently tighter at low F numbers but probably mainly because - even after tightening it all up - my Skywatcher focuser really isn't up to the task and I can't get consistent results moving in versus moving out. The other sometime big issue here is seeing - wherein the frame to frame variation in FWHM outweighs changes as you approach best focus. Maybe the bhatinov mask is a way to go? I do also wonder whether under marginal seeing your unguided approach works better than guiding and if some of the problem is chasing the seeing.

Tim

[Menno555]

Hi Tim

Well, my first version with processing was indeed not that good when it came with processing. The version you see below (2400px version on https://i.ibb.co/BjkzsnJ/M81-II.jpg is way better. Yesterday I learned a few new "tricks" for processing, also with noise reduction. I use Photoshop and I never payed attention to the Camera RAW filter. I really thought this was only for RAW-images but it works just as great for TIF-images. It is SO much better for processing nd also gives less color noise
The colors now are way better, it looks more "natural". And also more details: the dust lanes in the center for example are there now and in the arms there is a lot more going on

And yes, filters do help with a (full) moon sky. I used the Optolong L-Pro and that filters out the spreaded moonlight, keeping the background darker, giving more contrast. Still, details of an object will get lost due to the moonlight. Technically the L-Pro is no light pollution filter though: it's a multi narrowband filter (Ha, Hb, OIII, NII and SII) but the ranges are big enough to use it for multiple things. If you use it for example on M33, you will get a "normal" capture with a bit of Ha added.

And yes, stars will have the same relative size in between themselves. But indeed the combination of "flooding" pixels and processing makes them "bigger". I did look for a larger pixel size camera for my cope but these are just astronomical in price. My camera has a pixelsize of 4.78 µm while a pixelsize of around 9 µm would be better.

On the focus: I have no experience with guiding, so really couldn't tell. I can imagine though that it makes sense that if the guiding is doing to much corrections, it will have it's effect on sharpness and then it might look that the focus is off? And with my methode the movement is just steady because no corrections are made.
I also pay no attention on FWHM or whatever. I just use the Bahtinov and the Bahtinov Grabber software

[timh]

Hi Menno,

That is an impressive improvement making for an attractive image. It is taking me an awful long time to understand the capability of all of the various bits of post-processing software I have now accumulated.

You make a good point about the pixel size of the camera - but you could perhaps 2x BIN it? In fact I think that this can be done post capture (although SC has that as a capture option obviously) and then no need to capture the BIN2 darks and flats that are othewise needed. You can do it in PI software - probably in other software too? I haven't tried it myself but there is a discussion here on https://www.cloudynights.com/topic/6554 ... esampling/ and it might be interesting to try on your existing data set to see if simply resampling it gives a significant improvement in SNR?

Just for interest also here is an image of M81 which is quite comparable in that it was also accumulated using an 8 inch reflector but at F 4.5 and under ( relatively) darkish ~ Bortle 6 skies with no filters (other than UV/IR blocking). At F 4.5 the roughly 2h accumulation time should be about equivalent to your 10h at F10 in terms of the illumination of the image ? - however the F10 image scale is bigger so more of the total captured light contributes to the area of interest ...not sure whether the latter point actually matters though?

As well as 2h of RGB lights the attached image also has a little added luminance (which made no perceptible difference) and also about an hour of H alpha added to the red channel. To be honest, having discovered the technique, I got slightly carried away -- it is too much and looks like a smattering of tomato sauce everywhere. It is interesting to see though that while Holmberg IX has blue stars - which presumably formed recently - there is no obvious H alpha - so maybe it has run out of or been stripped of gas?

The main dilemma I have with the M81 image here is whether or not to invest any more time capturing lights to try and improve it? Clear sky time is the most precious resource and what to spend it on the biggest decision. At the moment I am on the page of probably another couple of hours to reduce the chrominance noise but not to expect to go any deeper unless I can get to a truly dark site? I like the brighter galaxies and the cores of M94, M82 and M106 for example are interesting under any conditions but the outer precincts are probably out of reach under most skies?

best wishes
TimH

Skywatcher 8" Newtonian, 0.9X reducer flattener, F 4,5, ASI 294 PROMC and ASI 294 PROMM at - 10C , HD2 guiding AII 120MM and 9 x 50 finder
187 X 40s lights, gain 124 ; 60 x 40s luminance ; 27 x 2min HA (7 nm Optolong) at gain 124.

[Menno555]

I see what you mean with going overboard Looks great though

And I really must read better sometimes. I totally missed your f/4.5
That totally explains the fact that you can get better/sharper detail, the light gathering is way more ... or different, I don't know the best description :p
I do know that with my f/10 the light is more "spreaded" (or however that's called). A bit like with a 25mm and 10mm eyepiece: the 25mm will give a brighter and sharper view over a larger area, there where the 10mm gives a dimmer, bit less sharp view but with more detail over a smaller area.
I can compare it myself with my Owl Nebula captures: with the ASI385MC camera it looks "fuzzier" in comparison with the ASI 071MC Pro which gives a lot bigger FOV. Yet in the 385 there is more "detail" hidden.

On the binning: I tried that. But with a color camera like mine it makes way more sense to scale down with processing. Plus when I do bin2, the sharpness is really less. I thought that was caused by my settings but it seems that that is a common thing with OSC.

And I will gather more data for M81. Have to wait for a really clear, moonless night and then with the Optolong L-eNhance.