The Jewel Box

Located at 60° South, the Jewel Box (in Crux)  is one of those southern gems which I keep returning to but this is the first time I’ve imaged this object with my ZWO astro-camera.

The cluster is a closely bound group of over a hundred stars, all very young – reputed to be ‘only’ about seven million years old. 

Most of them are blue ‘giants’ but at least one of the brighter stars is a ‘red supergiant’ – and this is easily seen when I show this object at public nights.

Unlike a lot of astronomical objects, it actually bears some resemblance to its name!

I followed the  exact exposure and gain levels which were recommended by the SharpCap “Brain” histogram tool – but I’m wondering, with this type of object, whether it  should be factored down a bit.

I had to locate the object by manually searching, because the EQ6 mount 3-star alignment routine was not aligning.

American date format? ✔   Time? ✔   Daylight Saving? ✔   Coordinates? ✔   Altitude✔  Hemispheres?  ✔   Polar alignment?   ✔

It has to be one of the above settings. I tried four times but each time I sent it to an alignment star it went somewhere else not even close. Even a 1-star alignment failed.

I checked the handset entries again in daylight the next day and they seemed correct……

It’s only five months since I resolved the last alignment issue I had with it.  😨


Object Details:

Designation: The Jewel Box Cluster, NGC 4755, Caldwell 94.
Constellation: Crux.
Visual magnitude:  +4.2
Apparent size:  10′ x 10′.
Diameter: 18.7 light years.
Distance:  6,400 light years.
Altitude: 47° above SW horizon.


Exposure: 2700 sec (45 minutes) 113 frames @ 23.9 sec
Gain:  92
Date:  2019-06-11
Location:  outer suburban.
Conditions:  clear.
Moon:  yes, FQM+1, 62° from target
Sky:  2.66 e/pixel/s  


Image acquisition software:  SharpCap, live stacked.
Image post-processing:  GIMP.
Cropping:   slight edge trim only.


Telescope: SkyWatcher Esprit  Type: 120ED triplet refractor
Focal: 840 mm F/7 Mount: SkyWatcher EQ6-R Pro
Camera: ZWO ASI 071 MC Pro Type: CMOS 28.4mm 16 Mpx
Optical aids: Flattener: Y; filter: N Guiding: No
Polar aligning: QHYCCD PoleMaster Polar Error: 03’ 50”


Jewel Box Cluster taken in 2015 with Canon 60D and 8″ Schmidt-Cassegraine telescope.

Geek Log:

[ZWO ASI071MC Pro]
Debayer Preview=On
Output Format=FITS files (*.fits)
Capture Area=4944×3284
Colour Space=RAW16
Hardware Binning=Off
Turbo USB=40
Frame Rate Limit=Maximum
Timestamp Frames=Off
White Bal (B)=50
White Bal (R)=53
Cooler Power=100
Target Temperature=-15
Auto Exp Max Gain=300
Auto Exp Max Exp M S=30000
Auto Exp Target Brightness=100
Mono Bin=Off
Anti Dew Heater=Off
Banding Threshold=35
Banding Suppression=0
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 © Roger Powell



  1. I just started following your blog and look forward to seeing some sky views new to me. Beautiful shot of the Jewel Box. Located 42˚ north in the central US, we see very different things.

    I had to look up Campelltown and saw it was not far from Sydney.

    Liked by 1 person

  2. Hi Jim, thanks very much for the follow.

    Yes, Sydney is to the north of my two observing sites. I know it’s there because I can see the ever-increasing light pollution in that direction.

    I look forward to reading your blog posts too.

    Best regards from Down Under. 🙃


  3. Hi Roger
    How do you get on with Sharpcap for deepsky work, I’ve tried it a few times with mixed results, I,m all for free software if it works for me that’s why I changed to Astrophotograpy Tool for deepsky imaging and only use Sharpcap for Planetary work however I tend to use Firecapture more now.
    The jewel box is a nice image, bet your pleased with the ZWO ASI071MC Pro.

    Liked by 1 person

  4. Hi Will,
    SharpCap is probably the only software I currently use which I am prepared to pay for the pro-version. I’m still gaining experience with it and feel that I need to fully understand its various features before considering what other products may offer.
    ‘Live Stacking’ and the ‘Brain’ function have been very useful in understanding how to set exposure levels to get an improved final stacked image, rather than chasing good individual subs. Also in lowering the desirability of long exposure subs when using a lower noise cmos camera.
    I was aware of only SharpCap and Firecapture when I bought the ZWO and I opted for SharpCap simply because it had been recommended by a friend. As I get a bit more experience, my thoughts may stray to alternative software – or I may opt to remain inside my comfort zone. We’ll see.
    However, thanks for asking and for prompting me about Astrophotography Tool! ✔


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