LBN564 and a few galaxies

[wimvb]

LBN 564 in Cassiopeia. What caught my eye when I was researching this nebula was the irregular galaxy ugc 12887 / pgc 73185 near the top of the image (about 240 Mly distant, with a brightness close to that of the galactic cirrus), as well the galaxies near the bottom (pgc 073101, about 180 Mly distant, very faint pgc 2307034, about 2.3 Gly distant). There are also several unidentified galaxies in the background.

This image is just shy of 6 hours integration time, of which 90 minutes L and the rest RGB. I combined the luminance data with the RGB data to create a synthetic luminance.

Telescope SkyWatcher MN190 with ZWO ASI294MM camera @ 0 gain.

[Adreneline]

Hi Wim.

I took the liberty of plate solving your image so I could be sure I was identifying the galaxies you identified in your post description above.

I recognise you point out that there are "several unidentified galaxies" in the image but I for one find it interesting just how few galaxies there are in the image. I am interested primarily in imaging nebula targets and so tend to "turn off" PGC objects in the PI Render AnnotateImage script otherwise the whole image turns blue with an overwhelming number of PGC objects. In this region there are just seven PGC objects! I have this naive and uneducated view that the density of galaxies ought to be pretty much uniform where ever you look - that is clearly not the case. There are huge regions devoid of catalogued galaxies - which just seems odd to me.

Thanks for another thought provoking and interesting image.

Adrian

 

[Ags]

11 hours ago, wimvb said:

elescope SkyWatcher MN190 with ZWO ASI294MM camera @ 0 gain.

Why 0 gain? Doesn't that mean you are not counting all the photons?

[Adreneline]

1 hour ago, Ags said:

Why 0 gain? Doesn't that mean you are not counting all the photons?

A Quick Look at the 294MM spec and graphs would help to explain it:

https://www.firstlightoptics.com/zwo-cameras/zwo-asi-294mm-pro-usb-30-cooled-mono-camera.html

 

 

[wimvb]

4 hours ago, Ags said:

Why 0 gain? Doesn't that mean you are not counting all the photons?

Any camera has its largest dynamic range at its lowest gain setting. This means that a stronger signal won’t saturate a pixel. When you increase the gain, you will get lower read noise, but also a lower saturation (full well, if you like). ZWO cameras have their highest saturation level at the lowest gain, in standard read out mode as well as in high conversion gain mode. The problem with the sensor in the ASI294 is that it doesn’t behave well at low gain values in high conversion gain mode. Using the camera at 0 gain means that I can choose longer exposure times and still have colour in the stars. If the total integration time is kept the same, I also have fewer exposures, and use up less storage space on my hard disk.

[Ags]

Your results speak for themselves (unlike mine 😭) but if you are not converting every photon to an electron, I can't see how you are not throwing away data. It's like saying a camera with 25% QE has great well depth and subs even 10 minutes long don't blow out stars. I can't see how a camera with 90% QE and tiny well depth wouldn't beat it with a lot more 1 minute subs. Yes the disk space of all those subs would be larger, but they would genuinely contain more data.

I'm not saying I am right, I must be missing something somewhere?

[wimvb]

1 hour ago, Ags said:

Your results speak for themselves (unlike mine 😭) but if you are not converting every photon to an electron, I can't see how you are not throwing away data. It's like saying a camera with 25% QE has great well depth and subs even 10 minutes long don't blow out stars. I can't see how a camera with 90% QE and tiny well depth wouldn't beat it with a lot more 1 minute subs. Yes the disk space of all those subs would be larger, but they would genuinely contain more data.

I'm not saying I am right, I must be missing something somewhere?

With low QE,  you don't get any electrons to begin with; it's only the electrons that are generated that count. One would think that a gain of, say, 4 e/ADU must introduce discrete levels, with lost intermediate steps, because only 4, 8, etc electrons are counted, whereas 1, 2, 3 fall below the detection threshold. But that's where stacking comes into play. Craig Stark, the creator of the PHD guiding software, wrote an article a long time ago, about how stacking will restore those intermediate levels and gain bit depth. It has all to do with noise. If noise is added to a constant (in time) signal, then even fewer than the 4 electrons needed, can lead to a pixel value at times reaching the next discrete level. Let's say that a pixel receives just one signal electron. Without noise, that pixel will always have a value of 0 ADU. But with noise, sometimes that pixel will reach 1 ADU. Because of that one signal electron, the pixel will reach 1 ADU more often than if it didn't have that electron. If the pixel has 2 signal electrons, then with noise, it will reach 1 ADU even more often. Now, stacking will add those ADU values and average them. The 1 electron pixel will reach an average value of 1/4 of the original ADU, and the 2 electron pixel will reach a value of 1/2  of the original ADU. This is what Stark argued. I recreated Stark's experiment and explanation here.

[Ags]

Thanks for the further explanation, I'll have to think this over!

Sorry to distract the thread from your great image, just trying to learn.