galaxies near NGC253

[Shiraz]

Hi
got a bit over an hour of good seeing on this, so decided to go for broke and bumped the gain to 200 on the ASI1600 - at which the subs were sky-limited in 20 seconds. The loss of dynamic range was more than compensated for by the short-sub improvement in FWHM and some sections of the session yielded subs with FWHM<1.5 arcsec.

I still have days of work ahead on this - the seeing was so good that the subs were slightly undersampled (at 0.76 arcsec sampling), so there will be a smidgin more resolution available from drizzle and with over 500x16mp subs, that will take a long time. For now though, this is a crop from the first quick evaluation stack of uncalibrated subs, showing some of the star formation regions in the galaxy and also some of the far distant galaxies that abound in the field. This is a long way from being a finished article, but I was so excited by the early signs of what the sky had provided that I had to post something :P. Thanks for looking. regards Ray

[plantnerd]

That is spectacularly impressive detail!

[Atmos]

That's amazing Ray!!

[batema]

Yes stunning detail. Wonderful.

[RickS]

Looking forward to the finished version, Ray! Don't take too long now that you've started teasing us :)

[DJScotty]

Very nice detail.
The ASI camera is a cracker!

[codemonkey]

Looks awesome so far, Ray, looking forward to seeing the finished product!

[Shiraz]

thanks very much folks.

This is going to take a lot of processing yet, but thanks for comments on an interim result.

Sorry that this looks like a teaser - I just didn't want to post the whole thing before I process it properly. Guess I let my enthusiasm get the better of me - oh well:P.

[alpal]

Hi Ray,
500 subframes! -
that's 1/22 of the noise & it looks as sharp as CHART32.

cheers
Allan

[topheart]

Wow!!

Tim

[Placidus]

Incredibly sharp. This is another world.

[Camelopardalis]

Crikey Ray :thumbsup: can you send some of that seeing this way please? ;)

[astroron]

Your finished product may have the galaxy in it discovered by Mike Sidonio
(strongman Mike)
Looks fantastic. :)
Cheers:thumbsup:

[Peter Ward]

Your excitement about the results to date is totally understandable

Very impressive. I'm really looking forward to seeing the entire field at that level of depth and resolution. :thumbsup::thumbsup:

[plantnerd]

What software are you using for Drizzle?
I have a 32 CPU Core workstation with 64GB Ram that might process your images pretty quick. Oh and the hard disk is PCI E SSD that reads at 1400mb per second to keep the CPUs fed with data.

I can process 2500 16MP images into a 5 Gigapixel mosaic in 56 Mins!

[strongmanmike]

Wow, I can see plenty of evidence of the many faint field galaxies in the background and filigree structure within 253 itself :eyepop:

Marcus will be hating you right now.....:lol:

Looking very spegtagular :D

Mike

[Shiraz]

thanks Allan - I have been using the ESO image as a guide, although my system cannot produce anything like the big scopes.


thank you Tim


Thanks M&T. it all comes down to seeing in the end - nice to have a bit of good stuff.


The seeing surprised me, but this site does best at the change of the seasons, when the nearby ocean is at about the same temp as the night air. During winter it is like imaging alongside a power station, with the sea about 10C hotter than the night air.


hi Ron. Unfortunately, I don't have Mike's galaxy in the field - pity really


thanks Peter - we shall see.


blimey that's fast Luis. I only have a quad I7 with 16G RAM, so it churns along relatively slowly. I plan to use both Nebulosity and PI for the deconvolution and choose the best result. Nebulosity in particular is slow with a large stack, but it can sometimes do better than PI in recovering resolution.

[Shiraz]

Thanks Mike. Seeing is still king. I doubt that it will get to the same level as Marcus' image, but I hope it will come out OK - now to find the time to process everything. Pity the field doesn't include your galaxy though - didn't think of trying for

[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:thumbsup:

[JA]

Looks wonderful :thumbsup:
Looking forward to the final image

Best
JA

[Shiraz]

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

[Shiraz]

thanks JA!

[Atmos]

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 :P

[marc4darkskies]

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

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]

Thanks Ray and Colin:thanx:
I am sure someone will hear my plea.:lol:
Cheers:thumbsup:

[silv]

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]

24

[Regulus]

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

Trevor

[andyc]

Fabulous detail there Ray! :eyepop:

[DaveNZ]

Wonderful image Ray. Which telescope were you using ?

[Shiraz]

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


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


thanks for the encouragement Trevor.


thanks Andy!


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

regards Ray

[Placidus]

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]

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 (http://www.sensorgen.info/OlympusOM-D-E-M1.html). 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]

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]

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 (http://www.cse.wustl.edu/~jain/cse567-11/ftp/imgsens/index.html)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]

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:lol:

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]

:eyepop::eyepop: