First light - DSO with ZWO ASI 174mm Cooled CMOS

[dylan_odonnell]

I know a few people have been wanting to see how this relatively cheap camera performs for deep space objects so here are my thoughts on first light. I got mine from Bintel in Sydney who I recommend highly.

I'm used to a very nice large frame CCD (QHY12) which has a huge resolution but a slow read out time. As soon as I took my first test sub on M42 (30 seconds) I realised how fast this camera was. It was completely over exposed. So I put it down to ONE SECOND and it was still overblown!

I turned the gain in the camera settings down to zero and went to 5 seconds and got the exposure that you see in the attached image. It's a mono cam though so I ran a series of exposures in Ha, OII and SII to process in the Hubble Palette (my first try actually).

This camera is fast, especially with my hyperstar shooting at f2. Oh my god, I set it to run a sequence of 32 exposures and went to get the next filter ready and it was finished. I barely had time to look at my phone between sequences.

In the end I used :

64 x 5s Ha
64 x 5s OIII
64 x 5s SII

Total 16 minutes integration time! (Celestron 9.25" Edge HD, Hyperstar III lens & filter drawer system, Baader high speed f2 Ha, OIII, SII filters, EQ6 Pro mount, PHD2 guiding w/ Celestron 80mm guidescope & ZWO 120mm)

The resultant image here is totally uncalibrated, no darks, no flats, no bias. The camera was cooled to -30c. You can see a couple of hot pixels.

The final image isn't as big as I'm used to, only 1775 x 1182px and without calibration there is horizontal banding which causes pretty much all the visible noise you see in this image.

For the price I think this is a great starter camera for anyone just starting with deep space. It might take a little extra care in processing but this camera is as fast as lightning. Would perform well with especially dim targets.

(POST UPDATED - tightened SII level for better HST effect)

d

[Slawomir]

That's very cool Dylan, thank you for sharing your experience with this camera :thumbsup:

Do you think that quick over exposure might have something to do with 12 bit ADC?

[dylan_odonnell]

Thanks! The camera did default to high gain settings to start, and 1 second did *just* blow out some of the trapezium. Changing to it's default "low gain" settings helped.

The 12bit ADC definitely affects the dynamic range of the image though and there is far less dynamic range than a 16bit CCD offers.

[John K]

Nice work Dylan,

What software did you use to manage the camera and capture with?

[Atmos]

Looking great for 5s exposures!

What you might find worthwhile is calculating the best gain. You can do it inside without a telescope, just point the camera at the roof without the cap on. You start at 0.01s exposures and the gain at 0, keep increasing the exposure time slowly until the average ADU count over the entire image no longer increases, this is full well capacity.

From there you slowly increase the gain at that exposure time until it hits ~65535 ADU. You've got a camera with 12bits of data, you don't want to lose any of that by using presets :)

[alocky]

What an impressive result! it almost looks like it will be capable of planetary style imaging of planetary nebulae!
Looking forward to seeing more results.
Cheers
Andrew.

[dylan_odonnell]

Thanks! I'm using Nebulosity 3, though it connects to the camera via the ASCOM driver so I imagine it would work with anything.

[dylan_odonnell]

I did not know that, thanks for the tip!

[dylan_odonnell]

Thanks! Yup, it's a relatively small chip too, so good for smaller, dim targets. I'll be using it mostly for planetary and solar of course where it really shines.

d

[rmuhlack]

except that you'd surely only see a value of ~65535 if you had a 16 bit camera (2^16 = 65536)... (unless your software scales the output values to a 16bit equivalent)...?

[Atmos]

I know that Maxim DL does, never taken images with Nebulosity so I am unsure whether it saves in 16 bit or not.

[Shiraz]

nice work Dylan.

thanks for posting results with this camera - very interesting and intriguing. My vague understanding is that these chips do an internal auto calibration at each power up and this results in a unique bias structure depending on what the cal converges to - so you need to record a new bias image set each time you turn it on - is this correct?