Messier 94 and 100

[Hughsie]

With galaxy season in full swing I reluctantly decided to use my StellaLyra RC8 to capture some of the smaller galaxies in view. I say ‘reluctantly’ as this beast as consumed time and extra funds to get it to a point where collimation looks reasonable. Couple that with getting my head round whether to bin or not to bin then throw in off axis guiding as well and I hope you can sense my pain.

So what do we have...

First up is Messier 94.

Equipment

• RC8
• SkyWatcher EQ6R-Pro
• ZWO ASI1600mm Pro Cool, Bin 2x2 Gain 139, offset 39.
• Chroma 1.25” LRGB filters
• ZWO 8 EFW
• OAG with Lodestar x2

Data

• Captured across 4 nights (22nd to 25th March 2022).
• Luminance 229 x 120s
• Red 70 x 120s
• Green 74 x 120s
• Blue 75 x 120s
• Darks, Flats and Flat Darks x 50 each.

 

Next is Messier 100 captured with the same equipment, however, this time camera binning was left at 1x1 and down sampled in PixInsight.

Data

• Captured across 2 nights, 1st and 2nd April 2022.
• Luminance 244 x 60s
• Red 41 x 120s
• Green 44 x 120s
• Blue 19 x 120s (clouds stopped play)
• Darks, Flats and Flat Darks x 50 each.

 

 

M94 suffers from being captured just after a half moon and more time should have been spent removing gradients. In both images there appears to be some colour bleed around the edge of the stars. Naturally all data was aligned and then the resulting master of each channel was aligned again. The capture of M100 then software binning in PixInsight seem to have produced a better image but then I have to weigh that up with the Moon not being present too. Finally, the brightest stars. In M94 the large star above the galaxy suffers with a glare between the diffraction spikes. I reduced the Luminance exposure time to 60s in M100 to counter this but it still remains (see large star in the bottom left). I don’t know if this is symptomatic of the ASI1600mm as I have seen it in my refractor images too.

All thoughts and feedback welcome. I am just waiting on the next clear night when I have resolved to complete a star test and hopefully fine tune collimation.

Thanks for dropping by.

John

 

 

 

[ollypenrice]

Those are great. In your place I'd want to be looking at the slightly saturated cores in both. What I've found effective is not to take short exposures for the cores but to do an image in which you only concern yourself with the cores and only use the RGB data.  With less signal it tends to be less over-exposed than the L.  You can then layer mask or otherwise blend the less-stretched core into the present LRGB.

Olly

[Hughsie]

1 hour ago, ollypenrice said:

Those are great. In your place I'd want to be looking at the slightly saturated cores in both. What I've found effective is not to take short exposures for the cores but to do an image in which you only concern yourself with the cores and only use the RGB data.  With less signal it tends to be less over-exposed than the L.  You can then layer mask or otherwise blend the less-stretched core into the present LRGB.

Olly

Thank you Olly.

For my shorter focal length scope (568mm reduced) I would typically use the RGB master at a low stretch, up the saturation and then blend in the L channel. Going by your comments, am I correct that I should stretch the RGB master further then blend in the L channel to suit?

Do you have any thoughts about lowering camera gain to increase full well depth to avoid over saturation of the cores? I have seen on Astrobin some images using a similar focal length (1600 mm) and gain as low as zero or slightly higher, say 75, well below unity gain for the ASI1600mm?

Thank you for your kind feedback, it is much appreciated.

John

[ollypenrice]

10 hours ago, Hughsie said:

Thank you Olly.

For my shorter focal length scope (568mm reduced) I would typically use the RGB master at a low stretch, up the saturation and then blend in the L channel. Going by your comments, am I correct that I should stretch the RGB master further then blend in the L channel to suit?

Do you have any thoughts about lowering camera gain to increase full well depth to avoid over saturation of the cores? I have seen on Astrobin some images using a similar focal length (1600 mm) and gain as low as zero or slightly higher, say 75, well below unity gain for the ASI1600mm?

Thank you for your kind feedback, it is much appreciated.

John

Hi John,

I would first finish the LRGB image and accept the cores as they are. You already have that.

I'd then open up the linear RGB and stretch it only for the quality of the core. I'd ignore the rest because it won't be used. The idea would be to get the outer parts of the core (or the area just around it) to a brightness as close as possible to that part of the main image. You need to do that in order to get a seamless blend later. However, I'd be using a stretch, probably done manually in Curves) to keep the core itself as free from saturation as possible. 

Next comes the blending of the gentler core with the rest. The proper way involves a layer mask. I'll use 'short' for the new RGB image and 'long' for the main LRGB here.

1 Copy-paste the short over the long as a layer. 

2 Add a layer mask for the top layer. 

4 Copy-paste the long onto the layer mask. Considerably increase its contrast to make the light parts lighter and the dark parts darker and then give it a big gaussian blur, maybe 3 to 5 in Ps.

5 Adjust the short till you see a seamless blend. Use levels or curves and the colour saturation tool for these adjustments.

Now for the bad boys' way! (It usually works on round targets like cores and stars...)

1 Paste the LRGB on top of the short RGB stretch.

2 Take a fully feathered eraser a little larger than the core and apply centrally over the core on the top layer. Now you can see the short RGB core in the context of the main image.

3 Play with the RGB layer in Curves till you get a seamless blend.

Before doing any of this, be sure to check that your RGB core isn't saturated at the linear stage. If it is, you'll need short exposures. I would only bother with RGB because the point of luminance is to get more signal and what we want here is less.

I can't help with the gain question since I've only recently started using CMOS but, as ever, I'd experiment.

Olly

[Hughsie]

Given the clouds I am in the process of reviewing all my old data and reprocessing it. Here is Messier 100 using the data from 2022.

 

 

[PatrickO]

I have no skill in DSO, but these are beautiful images. Well done.

[RobertI]

This looks great, lots of detail in the core now. More detail all round too. Great job. 👍

Edited February 10 by RobertI

[Hughsie]

6 hours ago, PatrickO said:

I have no skill in DSO, but these are beautiful images. Well done.

Thank you Patrick, I appreciate your comment. I just muck around with the data, throw it together and keep going backwards and forwards until I get where I want to be.

Edited February 10 by Hughsie

[Hughsie]

5 hours ago, RobertI said:

This looks great, lots of detail in the core now. More detail all round too. Great job. 👍

Cheers Rob. 2022 must have been my "blurry period" lol