Eta Carin-Ha

[Camelopardalis]

Folks,

I'd been experimenting with Ha late one night out in the bush and this is how it turned out.

The fast-enough 'frac (Esprit 100) and cooled CMOS (ASI1600) make for quite an interesting narrowband combo :D

This shot is 24x 3 minute subs.

Cheers,
Dunk

[glend]

Yes indeed Dunk. Nice field of view at the f 5.5. That looks like Unity at that sub length, is it? Did you try longer subs, or a mix to find where they might start to "over cook" ?

[Camelopardalis]

Yeah unity...I tried 5 minutes but it was overblown :lol:

Next opportunity I might drop the gain down to 75 and see if there's any more dynamic range to be had, but I don't reckon I'd see much difference.

[codemonkey]

Very nice Dunk :-)

Regarding going below unity in future, just keep in mind the fact that this is only a 12-bit camera, so you want to do lots of short subs which will get that effectively back to 16-bits (or above), lest you incur some posterization.

[Camelopardalis]

Thanks Lee!

I've gleaned lots of interesting nuggets about this camera from the "other side" but I'm also a believer in finding the sweet spot, which may vary from unit to unit.

According to Pixinsight, my camera has maximum dynamic range (a full 12-bits) at gain=75. I have captured a couple of subjects at that and I can't see the difference :lol: I've not noticed any posterisation either, maybe I'm just blind :lol: :lol:

[Atmos]

Looks better in yours than mine, slightly wider field :)

Disregarding the slight difference between each camera there is only a 22% increase in dynamic range between Gain 75 and Unity. Gain 75 has a little more than double the well depth BUT the read noise is lower at Unity so only about half the exposure time is needed to be read noise limited.

[Camelopardalis]

Thanks Colin! It was your HH that reminded me that I had these subs somewhere :D

I have to say, I'd been torn between unity and 75 with the subjects I'd imaged so far. When you put it like that, it makes unity a no brainer :thumbsup:

[Atmos]

From the single run of calibration frames that I used for my testing (there may be some variance if I did another run as there always is) I was getting 11.93 bit at Gain 75 and 11.25 bit at Unity. Now every camera is a bit different as well and if I run it again it may be different also.

Ray uses a Gain of 100 so your thought of half way between the two may be very well on the money :P

[RickS]

Looks good, Dunk!

[Camelopardalis]

I'd like to think we were being scientific about it, but it seems to be as much about balance as anything. Good to have the variable gain option IMO



Thanks Rick!

[Placidus]

Well done!

Extraordinary how far amateur astrophotography has come in the last ten years.

[Camelopardalis]

Thanks Mike & Trish!

Barely a year ago I'd have thought that it wasn't possible...

[SimmoW]

Nice detailed images there Dunk. I've settled on 75 myself, seems to get me the best star colours. No science used, just tried various length subs at differing gains to decide the setting visually. I believe my eyes. But I may be lucky, had some bloke in CN saying he didn't believe that I could do 10 min subs and still get good star colour.

Hoping you do yet more experiments on varying settings, but the weather is back to intermittent here and whenever the skies clear I just get greedy for photons!

[Camelopardalis]

Thanks Simon! I should probably post a shot of the core at full resolution ;)

I'd imagine there are at least a few variables at play in getting good star colour. I've used 200 and been happy with the results too :shrug: it's a very versatile camera!

[Camelopardalis]

For those that are curious...here's a crop around an area with contrast/details. This is 100% resolution, barring saving as a JPEG of course :screwy:

When processing, I haven't "progressed" to masking regions and applying different levels of enhancement, so I look at the image and see what works well across a few carefully selected regions before picking the settings I like best.

And just keep in mind...this is 72 minutes of exposure time with a 4" apo, I'm sure it could be improved upon :D

[cometcatcher]

Looks very good Dunk!

[Camelopardalis]

Thanks Kevin!

[codemonkey]

Looks great to me, Dunk, if there's any posterisation there then my eyes aren't good enough to detect it. I'd be very happy with that data :-)

[Camelopardalis]

Thanks Lee - it just makes me wonder what it'd be like with a bigger scope ;)

[strongmanmike]

Nice Dunk :thumbsup: the Eta neb looks quite magnificent in B&W and I agree with M&T, when I compare with work I did over 30 years ago with film and cold cameras etc....the mind boggles :eyepop: :)

Mike

[Camelopardalis]

Thanks Mile! It's very tricky extracting any contrast out of the wedge of cheese and balancing the rest of the field too.

Maybe if I was braver I'd post my RGB too ;)

[kkara4]

wow Dunk, i finally got round to checking this out! great effort, it looks fantastic, and the stars look as round as they can be from being made up of squares :P.

sadly, i have yet to even get metaguide guiding my mount properly yet. :rofl:. i have a long way to go, ill be stoked when i get something that even resembles what you have :eyepop:

[Camelopardalis]

Thanks Krishan! The EQ6 is indeed quite capable of round stars :P