ngc 7686

[wimvb]

NGC 7686 is a small open cluster in Andromeda, consisting of approximately 80 stars. Its magnitude is 5.6 and it covers about 15 arc minutes of the night sky.

Imaged during a full moon on the night of December 3rd.

Image capture details:

SW 150 PDS on a SW AZ EQ6 mount

ZWO ASI174MM-Cool camera at -30 C, 0 gain

no guiding

Equipment control: Ekos/Kstars (Windows) with INDI (Linux on Raspberry Pi).

R, G, B about 75 best frames of 100 per filter at 30 seconds each. Total integration time just under 2 hours. I would have gone for longer exposures, if it hadn't been for the moon.

Processed in PixInsight, using photometric colour calibration, and @sharkmelley's arcsinh stretch to bring out the colour in the stars.

Only the day after did I notice moisture in my tube. This caused the bright area around the main star. Weather permitting I might just revisit this target to get a more decent image.

(click on image to enlarge)

[Allinthehead]

Still a nice image despite the moisture problem. I must try that arcsinh stretch.

[MikeODay]

Wonderful image Wim.  I really like the colours of the stars.

[wimvb]

2 hours ago, Allinthehead said:

Still a nice image despite the moisture problem. I must try that arcsinh stretch.

 

2 hours ago, MikeODay said:

Wonderful image Wim.  I really like the colours of the stars.

Thanks guys, I like it too. And this cluster seems rarely imaged, that's why I decided to post it here. The arcsinh stretch, together with photometric colour calibration, is much better at star colours than the standard histogram stretch or masked stretch. Here I applied it twice. First I used the preview to find out the maximum total stretch (was about 700), then I applied the stretch twice with strength = square root of this max value. In this case strength = 25. Each stretch with a new value for the black point.

[gorann]

Actually Wim, from an artistic perspective maybe that moist made the image more interesting, making the cluster shine. Maybe it is my old eyes and dirty glasses but a shine around bright stars looks natural to me. Doing star clusters at full moon with short exposures is a good idea!

[wimvb]

3 hours ago, gorann said:

a shine around bright stars looks natural to me.

Maybe it's the constant cloud cover and haze that makes us believe the shine should be there. But I agree, it isn't entirely unpleasant.

Imaging star clusters is about the only thing one can do under a full moon. The cluster actually is more varied in star colour than I first thought. It would be nice to reshoot it under better conditions. Otoh, I also want to image fainter stuff, so I do hope there will be a few clear nights when the moon is out of the way.

[toxic]

very nice wim 

[wimvb]

5 minutes ago, toxic said:

very nice wim 

Thanks, Chris. With the few gaps we've had lately, I basically grab whatever is within reach. And under a full moon lighting up my gear, clusters are the only possible target. At least there's less frost on the scope, so the air is getting drier. The moisture on the mirror probably got there when I stored the cold scope last time.

[gorann]

2 hours ago, wimvb said:

Maybe it's the constant cloud cover and haze that makes us believe the shine should be there. But I agree, it isn't entirely unpleasant.

Imaging star clusters is about the only thing one can do under a full moon. The cluster actually is more varied in star colour than I first thought. It would be nice to reshoot it under better conditions. Otoh, I also want to image fainter stuff, so I do hope there will be a few clear nights when the moon is out of the way.

Star clusters are nice, but not as exciting as nebulas and galaxies so I doubt you would be turning your data starving equipment towards a star cluster when the moon is gone and the sky finally clears, which it will one day.

[wimvb]

You're right of course. But that hasn't kept me from posting a cluster image in the rgb challenge subforum. Two moonlit clear nights in a row. And I also managed to get some colour data on ngc 206 in the Andromeda galaxy. With a dry tube this time.

[gorann]

I had missed those subforums. Maybe I will get something to submits to the RGB challenge. What are the rules?

[wimvb]

The rules are simple, but darn near impossible to follow: you need clear nights during the challenge period.

The precise wording of the rules is in the first posted topic in the subforum. This challenge is aimed at DSLR imagers, but mono is also accepted.

 

[Star101]

Imaging Challenge #9

I was thinking of putting my Orion M42 in for that but just checking...It was taken on 26 Nov  lol

[lux eterna]

Over the years I have been appreciating star clusters more and more - and this is a beauty with nice colors and background. Just add a big screen and some nice music, and the waiting for clear skies is not so hard.

Ragnar

[MarsG76]

Moisture or not, still looks like gems spilled in the sky...

I had the rear cell haze over on me in the past, gives a soft focus 70s adult movie look... 

Are you using a dew heater?

[wimvb]

4 hours ago, MarsG76 said:

Are you using a dew heater?

On the secondary only. But I do have a small fan behind the primary. This is surprisingly good at keeping dew away.

The moisture on my primary was most likely caused by me putting the cold scope away in a warm shed.

[MarsG76]

2 hours ago, wimvb said:

On the secondary only. But I do have a small fan behind the primary. This is surprisingly good at keeping dew away.

The moisture on my primary was most likely caused by me putting the cold scope away in a warm shed.

I went the same option, heat the secondary and just 3 fans behind my primary on my SW14 Dob.