Celestial hemisphere:  Northern  ·  Constellation: Cassiopeia (Cas)  ·  Contains:  IC 1795  ·  NGC 129  ·  NGC 281  ·  NGC 663  ·  NGC 7789  ·  NGC 7790  ·  NGC 896  ·  The constellation Cassiopeia (Cas)  ·  The star Caph (βCas)  ·  The star Navi (εCas)  ·  The star Ruchbah (δCas)  ·  The star Schedar (αCas)  ·  The star γCas  ·  The star ηCas  ·  The star θCas  ·  The star κCas  ·  The star ρCas  ·  The star υ2Cas
Getting plate-solving status, please wait...
Cassiopeia and the Northern Rim of the Milky Way, David McClain
Cassiopeia and the Northern Rim of the Milky Way
Powered byPixInsight

Cassiopeia and the Northern Rim of the Milky Way

Getting plate-solving status, please wait...
Cassiopeia and the Northern Rim of the Milky Way, David McClain
Cassiopeia and the Northern Rim of the Milky Way
Powered byPixInsight

Cassiopeia and the Northern Rim of the Milky Way

Equipment

Loading...

Acquisition details

Loading...

Description

A loose composite of 3 frames, 7 x 10 deg FOV, covering the constellation Cassiopeia, and showing the northern rim of our Milky Way galaxy. Shot with a severely red-chellenged stock (unmodified) Canon EOS-6D camera and a Canon 200 mm FL F:2.8 lens. Each frame used the background from 5 x 5 mins at F:2.8 and the stars from 5 x 5 mins at F:8. These are all unguided subs.

Not a perfect mosaic, but close enough. The image gives a nice sense of scale, which is what I wanted. You can see the trail of stars leading from the double cluster just off the lower right of the image. Reflection nebulae are visible near Gamma Cas in the center of the image.

I got tired of the postage-stamp FOV from the HyperStar C8 + ATIK 490 camera, and went back to the Canon EOS 6D to recapture that missing sense of scale.

After trying for several hours, I finally succeeded in making a (more) proper mosaic of the region. It actually took me the whole day to figure out a proper workflow in PixInsight, to reach the approximate balance between frames. That was a real challenge.

Also, we are working very close to the quantum limits of the system, and it is very easy to overdo the processing and start picking up camera artifacts that look like they could be Milky Way structure, but aren't. The hint is in seeing circular arcs or vertical / horizontal structure that is the same in every image. If you see that, then you know you've stretched too far.

My analysis of the Canon EOS 6D sensor shows that at ISO 400, the camera operates essentially at nearly 10 bits of dynamic range. Ignore the fact that it uses a 14-bit A/D. The dynamic range is the full well depth at this speed, divided by the readout noise. At ISO 400, I have a full well depth of around 6450 e- and a readout noise of 8 e-, so there are only 860 steps from nada to saturation, i.e., just under 10 bits, or 7.3 magnitudes.

So, while this is a PNG image, the FITs file contains lots more detail and depth than you can see here. This is just a sketch, so to speak. But if you spot any 12th magnitude stars in the image, then I must be saturating on 5th magnitude and brighter.

I shoot all my images at ISO 400 speed, since the analysis of others has shown this to be an optimal setting with respect to noise levels and sensitivity. There is no free lunch. Higher ISO settings increase the readout noise and diminish the overall dynamic range.

Comments

Revisions

  • Cassiopeia and the Northern Rim of the Milky Way, David McClain
    Original
  • Final
    Cassiopeia and the Northern Rim of the Milky Way, David McClain
    B

Sky plot

Sky plot

Histogram

Cassiopeia and the Northern Rim of the Milky Way, David McClain