M106 LRGB

[Clarkey]

It was a rare occasion when one of the weather forecasts was right last night. I managed to get about 5 hours on M106, before the cloud rolled in. 2 hours luminance and 1 each of RGB. Given my location and the first quarter moon I am not too displeased with this one. As always, it could do with a little more data....

Taken with a Stella Lyra RC8 reduced down to F6 and an ASI1600MM. Constructive criticism and comment welcome as ever.

[MartinB]

That's is really nice, plenty of detail in the core and beautifully smooth outer regions.  Have you thought about doing some Ha?  There are some lovely Ha "jets" in there.

[Clarkey]

55 minutes ago, MartinB said:

That's is really nice, plenty of detail in the core and beautifully smooth outer regions.  Have you thought about doing some Ha?  There are some lovely Ha "jets" in there

Thanks for your kind comments Martin. I'll have a go at the Ha next time I get a weather window. Maybe May😂 Thanks for the tip.

[tomato]

Great depth, detail and colour, nice framing too. And with the moon up too!👍

[vlaiv]

What did you use to reduce FL on RC?

By the way - you should look into incorporating at least bin x2 (or optimally x3 for this image) in your work flow - it will give you SNR boost and make processing much easier.

[Clarkey]

16 minutes ago, tomato said:

Great depth, detail and colour, nice framing too. And with the moon up too!👍

Thanks tomato.

4 minutes ago, vlaiv said:

What did you use to reduce FL on RC?

By the way - you should look into incorporating at least bin x2 (or optimally x3 for this image) in your work flow - it will give you SNR boost and make processing much easier.

It was reduced using a TS CCD47 reduced to about 0.73. I know the stars are a little out of shape - my scope needs collimating. I'm just waiting for some kit to do it. I know in theory you can do it with a Cheshire and a stars for closer alignment - but I am being a bit of a coward!

I have tried binning but it did not seem to make much difference. I tried binning in the camera and binning in software (Affinity) but I saw no significant difference. I am not sure the best time to bin the data. Should I bin each channel before combining, after combining but before stretching, or towards the end of processing? Obviously being a CMOS there are not huge benefits like with CCD. However, my slow PC would certainly speed up!

[vlaiv]

3 minutes ago, Clarkey said:

I have tried binning but it did not seem to make much difference. I tried binning in the camera and binning in software (Affinity) but I saw no significant difference. I am not sure the best time to bin the data. Should I bin each channel before combining, after combining but before stretching, or towards the end of processing? Obviously being a CMOS there are not huge benefits like with CCD. However, my slow PC would certainly speed up!

You should bin at linear stage, either after calibration and before stacking or stack once it is finished.

What software are you using for stacking?

CMOS and CCD binning provides almost the same level of benefit - only difference being in level of resulting read noise. Here CCD has slight edge, but CMOS sensors have lower read noise to start with so that evens out the playing field.

6 minutes ago, Clarkey said:

It was reduced using a TS CCD47 reduced to about 0.73. I know the stars are a little out of shape - my scope needs collimating. I'm just waiting for some kit to do it. I know in theory you can do it with a Cheshire and a stars for closer alignment - but I am being a bit of a coward!

Your stars look rather decent.

Here is crop form "worst" corner at good sampling rate (x0.5 or about 1.32"/px) :

Does not look bad at all.

[Clarkey]

28 minutes ago, vlaiv said:

Your stars look rather decent.

Here is crop form "worst" corner at good sampling rate (x0.5 or about 1.32"/px) :

I use APP for stacking and initial combining of LRGB. I'll try binning the linear image before processing and see what difference it makes. Before, I tried it in the camera and after the initial stretch but I saw minimal benefit.

28 minutes ago, vlaiv said:

Your stars look rather decent.

Here is crop form "worst" corner at good sampling rate (x0.5 or about 1.32"/px) :

The image has already been cropped slightly as the edges were not good despite calibration frames and gradient removal. On the full size image the corner stars a out of shape. This seems to be exaggerated by the reducer.

[vlaiv]

2 minutes ago, Clarkey said:

The image has already been cropped slightly as the edges were not good despite calibration frames and gradient removal. On the full size image the corner stars a out of shape. This seems to be exaggerated by the reducer.

Well, image is ~ 4400 x 3175px, so I assumed that you cropped about 100 or so pixels on each side due to aggressive dithering.

According to pixel scale (I measured distance between two stars and compared to Stellarium angle measure), it looks like reducer was working at ~0.7165 (assuming original FL is 1624mm, but that will vary by few mm depending on distance between mirrors due to collimation).

This scope should cover APS-C sized sensor without too much issues in the corners. That would be around 27-28mm on diagonal.

ASI1600 has 22.2mm diagonal and if we divide that with 0.7165 we get - ~30.98 or 31mm. That is probably a bit too much although TS website says that sensors up to 30mm can be used without flattening.

Maybe this reducer should be kept at 0.75 max - that would give 22.2 / 0.75 = 29.6mm

I also have this reducer, but when I tried it once - I did not really like what I saw. Maybe I was trying too much reduction. Will need to give it another go with less reduction - up to x0.75

[Clarkey]

Thanks Vlaiv.

The 0.73 was an estimate based on the TS look up table and the spacing. It may well be slightly lower. At this reduction it is not too bad. There is a small amount of vignetting (which is uneven due to the collimation) but this calibrates out. When I collimate it will give me a better idea of the reducer performance. I know the collimation is out as even with a Cheshire as I can see the secondary is a long way off. Optically it might not be too far out, but mechanically it is. This might be linked to focuser tilt but until I start to adjust it, I won't know.

I think the reducer is certainly worth using. Imaging at 1200mm really helped with the exposure times needed. Even binning 2x2 this gives a good pixel scale and if I happen to get an exceptional night of seeing (it does happen very occasionally) using 1x1 would be about right.

Interesting about the pixels though. I am pretty sure the image was cropped harder than 100 px but I don't have the original files on this computer. I wonder if AP re-sizes the cropped image to the original scale? Something I will look into.

[Clarkey]

14 hours ago, vlaiv said:

You should bin at linear stage, either after calibration and before stacking or stack once it is finished.

Tried again binning the stacked channels. I the black point is slightly different but is there a significant noise reduction? It is processed slightly differently so maybe difficult to tell.

[vlaiv]

16 minutes ago, Clarkey said:

Tried again binning the stacked channels. I the black point is slightly different but is there a significant noise reduction? It is processed slightly differently so maybe difficult to tell.

Yes, background is much nicer. I think you might pushed saturation a bit too far this time?