galaxies near NGC253

[Shiraz (Ray)]

Originally Posted by astroron

Yes it's a pity you didn't remember Mikes galaxy, Ray
It's 253 season and I look at all the images being published for even a hint of Mikes galaxy,but none so far
Come on all you astrophotographers go deep enough to capture Mikes galaxy.
Cheers

just had a closer look and the main galaxy and Mike's do not fit in the same field on my system.

[Shiraz (Ray)]

Originally Posted by JA

Looks wonderful
Looking forward to the final image

Best
JA

thanks JA!

[Atmos (Colin)]

Originally Posted by astroron

Yes it's a pity you didn't remember Mikes galaxy, Ray
It's 253 season and I look at all the images being published for even a hint of Mikes galaxy,but none so far
Come on all you astrophotographers go deep enough to capture Mikes galaxy.
Cheers

The problem is that most of us don't have the FOV required to get it Those thy do are imaging through a straw! Like myself mind you

[marc4darkskies (Marcus)]

<1.5 arcsec seeing eh? You're dead to me Ray!

I had good seeing for my 253 - but it was still a lousy 1.8ish arcsec for a 3 hour stack. This looks outstanding so far - looking forward to the final result!

[astroron (Ron)]

Thanks Ray and Colin
I am sure someone will hear my plea.
Cheers

[silv (Annette)]

Reminds me of a German lullaby "Weisst Du wieviel Sternlein stehen... Gott der Herr hat sie gezählet, dass ihm ja nicht eines fehlet..."
Do you know how many stars there are? The good Lord has counted them all to not miss a single one.

Has someone counted them all? The galaxies in the photo?

[silv (Annette)]

24

[Regulus (Trevor)]

That's an impressive start Ray, and I am looking forward to the end result. Such an interesting project!
Well done.

Trevor

[andyc (Andy)]

Fabulous detail there Ray!

[DaveNZ (Dave)]

Wonderful image Ray. Which telescope were you using ?

[Shiraz (Ray)]

Originally Posted by marc4darkskies

<1.5 arcsec seeing eh? You're dead to me Ray!

I had good seeing for my 253 - but it was still a lousy 1.8ish arcsec for a 3 hour stack. This looks outstanding so far - looking forward to the final result!

thanks Marcus. that's what my stack was too, but the seeing was quite a bit better for part of the time.

Originally Posted by silv

24

Hi Silv - love background galaxies as well. gosh it's a big place out there.

Originally Posted by Regulus

That's an impressive start Ray, and I am looking forward to the end result. Such an interesting project!
Well done.

Trevor

thanks for the encouragement Trevor.

Originally Posted by andyc

Fabulous detail there Ray!

thanks Andy!

Originally Posted by DaveNZ

Wonderful image Ray. Which telescope were you using ?

thank you Dave. the scope is a 10inch f4 Skywatcher.

regards Ray

[Placidus (Mike and Trish)]

Ray, one thing I'm not understanding is the definition of the gain of 200. Do you know what are the units of the gain? The "gain" of a chip is often reported (irritatingly) in photo-electrons per ADU. For example, on the 16803 chip in our CG16M the "gain" is something like 1.8 photo-electrons per A/D count. A higher "gain" means you need more photo-electrons to register a count, so you get a darker image. I'm guessing from context you're describing something quite different.

We're so impressed by what you and others are doing with the ZWO camera we had a look at their web site. To our delight they actually offer a developer's SDK, so we might be able to integrate a future version into our system.

[Atmos (Colin)]

Originally Posted by Placidus

Ray, one thing I'm not understanding is the definition of the gain of 200. So you know what are the units of the gain? The "gain" of a chip is often reported (irritatingly) in photo-electrons per ADU. For example, on the 16803 chip in our CG16M the "gain" is something like 1.8 photo-electrons per A/D count. A higher "gain" means you need more photo-electrons to register a count, so you get a darker image. I'm guessing from context you're describing something quite different.

We're so impressed by what you and others are doing with the ZWO camera we had a look at their web site. To our delight they actually offer a developer's SDK, so we might be able to integrate a future version into our system.

The "gain" is, when in a DSLR like this chip is from, the ISO. From memory it is the same chip as found in this camera. As the gain is increased the read noise drops as does the dynamic range. At a gain of 139 it has an actual gain of 1, meaning 1e-/ADU.

[Shiraz (Ray)]

M&T

The chip has variable (inverse) gain that is controlled by a "true" gain number that sets the on-board conversion ratio (a higher gain number gives more ADU per electron). The translation between the gain number and the (inverse) gain is provided on the website charts - 200 is 20"db" gain although it is not specified "referred to what" - anyway, from the charts, a gain number of 200 corresponds to an (inverse) gain of ~0.6e/ADU with 12 bits output.

Then to make it a bit more complicated, the (hardware or the software?) changes the data from 12 bits to 16 bits by padding the bottom 4 bits with zeros. This is effectively an additional "true" gain of 16x, so the (inverse) gain in 16 bit ADU terms is ~0.6/16 e/ADU. ie gain 200 corresponds to an (inverse) gain of ~0.0375 e/ADU. At this setting, the well depth is only ~2000e, but the read noise has dropped to <1.5e.

I really hope this is some help - it was bad enough that everyone started calling the e/ADU conversion ratio a "gain". But then ZWO introduced a "true" gain number and also neglected to mention the hidden additional true gain of converting from 12 bits to 16 bits. Aaaargh.

if you are thinking about incorporating the 1600 into your acquisition software, perhaps be aware that it uses a streaming mode of USB3, which apparently puts heavy demands on the PC and doesn't tolerate faults. I am out of my depth on the details, but as far as I could tell, none of the standard acquisition packages worked properly when the 1600 was first released and the SGpro developers in particular had to modify some memory management? aspects of their package to make it work reliably.

[Placidus (Mike and Trish)]

Originally Posted by Shiraz

M&T

The chip has variable (inverse) gain that is controlled by a "true" gain number that sets the on-board conversion ratio (a higher gain number gives more ADU per electron). The translation between the gain number and the (inverse) gain is provided on the website charts - 200 is 20"db" gain although it is not specified "referred to what" - anyway, from the charts, a gain number of 200 corresponds to an (inverse) gain of ~0.6e/ADU with 12 bits output.

Then to make it a bit more complicated, the (hardware or the software?) changes the data from 12 bits to 16 bits by padding the bottom 4 bits with zeros. This is effectively an additional "true" gain of 16x, so the (inverse) gain in 16 bit ADU terms is ~0.6/16 e/ADU. ie gain 200 corresponds to an (inverse) gain of ~0.0375 e/ADU. At this setting, the well depth is only ~2000e, but the read noise has dropped to <1.5e.

I really hope this is some help - it was bad enough that everyone started calling the e/ADU conversion ratio a "gain". But then ZWO introduced a "true" gain number and also neglected to mention the hidden additional true gain of converting from 12 bits to 16 bits. Aaaargh.

if you are thinking about incorporating the 1600 into your acquisition software, perhaps be aware that it uses a streaming mode of USB3, which apparently puts heavy demands on the PC and doesn't tolerate faults. I am out of my depth on the details, but as far as I could tell, none of the standard acquisition packages worked properly when the 1600 was first released and the SGpro developers in particular had to modify some memory management? aspects of their package to make it work reliably.

Thanks so much, Ray. That makes complete sense now. And thanks for the warning about the brittle USB3 interface. My next job is to start to understand the physics of why increasing the "true" gain reduces the read noise. I found an old and out-of-date article on the electronics of a CMOS pixel which shows the presence of a per-pixel mosfet amplifier (must have an input impedance of tera-ohms not to deplete the charge during the exposure, and runs off the smell of an oily electron) that measures the charge. If that is where the "true" gain is applied, (i.e. assuming the top FET of the right hand pair in the diagram) before the A/D converter, I can see how it might reduce both the read noise and the well depth, though I'd like to understand better.

Sorry about the appalling typo in my original question, where I put "So you ..." instead of "Do you ...?"

Thanks Colin also for the extra info. It all helps.

Best,
Mike

[Shiraz (Ray)]

FWIW, my interpretation is that the way the amplification is split between the charge converter on each pixel (or maybe pixel group?) and the final ADC is the key. When the gain up the pixel end is high, both the signal and the pixel read noise contribution feeding into the ADC are amplified. The amplified pixel read noise simply overwhelms the fixed read noise contribution from the ADC and the S/RN drops to be that of the pixel at high gain. Expressed in terms of photoelectrons, the total read noise decreases as the gain increases. If you find a better or more accurate description of the actual mechanism, would be very grateful if you would post it.

I didn't see the typo - I can't ever see my own either

edit: I guess that it is a little bit like the photomultiplier process where gain is applied up front and any electronic noise that comes along further down the chain is completely swamped.

[graham.hobart (Graham stevens)]