Gem Cluster

A Southern Hemisphere object.

Object Details:

NGC 3293
Constellation: Carina.
Visual magnitude: +4.7
Apparent diameter: 6.0 arc-min. (about one fifth of a Lunar Diameter).
Actual diameter: 13.2 light years.
Distance: 7,600 light years.
Altitude: 57° above SE horizon.

Also visible:

Also visible in this image are the outskirts of the Carina Nebula (bottom).


Exposure: 45 min
Date: 2018-03-17.
Location: Leumeah, NSW.
Environment: outer suburban.
Sky: mostly clear.
Moon: New Moon.
Image acquisition software: SharpCap.
Image post-processing:  Deep Sky Stacker > GIMP.
Cropping: no.

Imaging telescope: Skywatcher Esprit 120ED Super APO triplet refractor.
Focal length: 840 mm, focal ratio: f/7.
Imaging camera: ZWO ASI 071 MC Pro.
Guiding camera: Orion StarShoot.
Guiding control software: PHD2.
Guiding accuracy: 0.8″ rms approx.
Telescope mount: SkyWatcher EQ6-R.
Polar aligning method: QHYCCD PoleMaster.
Polar alignment error: 36 arc-min (!)
Field flattener: yes; filter: no.

Observing Notes:
This particular evening was dedicated to resolving the issue of Synscan providing poor celestial alignment, which has dogged me for months. As a last resort, I hit the ‘factory reset’ button and followed up with a perfect 3-star alignment!

I still had issues with my Polemaster and found out the next day that the camera lens had worked loose.

I also discovered that saving the images to tiff files produces black and white images from a colour camera. With all that nebulosity, this image might have looked much better in colour!

SharpCap Camera Settings:

[ZWO ASI071MC Pro]
Debayer Preview=On
Output Format=TIFF files (*.tif)
Capture Area=4944×3284
Colour Space=RAW8
Hardware Binning=Off
Turbo USB=80(Auto)
Frame Rate Limit=Maximum
Timestamp Frames=On
White Bal (B)=55(Auto)
White Bal (R)=38(Auto)
Cooler Power=100
Target Temperature=-10
Auto Exp Max Gain=300
Auto Exp Max Exp M S=30000
Auto Exp Target Brightness=100
Mono Bin=Off
Anti Dew Heater=On
Apply Flat=None
Subtract Dark=None
#Black Point
Display Black Point=0
#MidTone Point
Display MidTone Point=0.5
#White Point
Display White Point=1

Image © R.Powell


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