Crescent – CDK reducer first light

Crescent – CDK reducer first light

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Imaging Telescopes Or Lenses : Planewave CDK12.5
Imaging Cameras : QHYCCD QHY268 M
Mounts : Astro-Physics 1100GTO
Filters : Chroma H-alpha 3nm Bandpass 50 mm · Chroma OIII 3nm Bandpass 50 mm
Software : Pleiades Astrophoto PixInsight · Stefan Berg Nighttime Imaging ‘N’ Astronomy (N.I.N.A. / NINA) · PHD2
Guiding Cameras : ZWO ASI290MM

Acquisition details

Dates : Aug. 19, 2021
Frames : Chroma H-alpha 3nm Bandpass 50 mm: 33×300″(2h 45′) (gain: 56.00) bin 2×2 , Chroma OIII 3nm Bandpass 50 mm: 24×300″(2h) (gain: 56.00) bin 2×2
Integration : 4h 45′
Avg. Moon age : 11.57 days
Avg. Moon phase : 88.90%


The Crescent Nebula

An emission nebula about 5000 light-years away from Earth.
The result of the collision is a shell and two shock waves, one moving outward and one moving inward. The inward moving shock wave heats the stellar wind to X-ray-emitting temperatures.
This “narrowband” image captures Ionized Hydrogen (red) and Oxygen (blue-green)

First light with the CDK 0.66x reducer

With limited clear dark skies available, I’ve been trying to maximize the system efficiency and “speed”.

The CDK 12.5 (318mm aperture) is now operating at fast focal ratio of f/5.25 and a focal length of 1670mm.

The image scale is still under 1 arcsecond/pixel (binned) which was my target given the seeing here is typically 2.4 to 2.6 arc seconds.

The QHY268m performs admirably here.

The smaller pixels are binned 2x to create 7.5 micron pixels to further increase the signal.

Its extremely low read noise of only 1.5e coupled with the very high QE of 92% allows for

very fast and clean data capture.

The 16bit ADC, almost negligible dark current and the lack of amp glow are added bonuses!

Moderate light pollution also is an issue and the 3nm narrowband filters help block out much of the unwanted light.

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