D800E night sky shots

Started Mar 21, 2013 | Discussions
Jack Hogan
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Re: D800E night sky shots: Fabulous. ISO?
In reply to Astrophotographer 10, 11 months ago

Astrophotographer 10 wrote:

So ISO 1600 things peak on a noise.dynamic range basis. Interesting. So then to optimise the exposure I am looking at what length tracked exposure do I get good exposure at ISO1600.

My suggestion would be to choose Exposure (ss and f/number) independently of ISO: for instance in your Rho Ophiuchi 10x30s stack at f/2.8, you chose 30s and f/2.8 for good technical reasons - so stick with them.  Then set ISO at base and increase it until you reach 1600 or you start clipping desirable highlights - whichever comes first.  It looks like in the case above you would have set it at 1600, so the out of camera images would look a stop darker than you are used to.  Not a problem, you can correct brightness to your delight in the raw converter without a SNR penalty, per my previous post.  Using ISO 3200 like you did did not give you a cleaner image, but it did reduce your available DR by 1 stop unnecessarily, which looks like would have been useful.

Do you understand why the 5D3 and other Canon graph looks so wildly different in shadow DR than D800?? Does it mean for a 5D3 ISO3200 is more optimum?

Yes, if you want to maximize SNR with a 5D3 in a case such as the one above you would HAVE to go to ISO3200 at the expense of 1 stop of DR.  The reason is that Canon's ADC implementation has not progressed as much as the competition over the last few years so they have less latitude and more often need to compromise SNR for DR and vice versa.  Looking at their performance at DxO it appears that in a situation such as this the D800e SNR performance at ISO 1600 (or 3200/6400 - don't forget it's one and the same since it seems to be done digitally after 1600) would be better than the 5D3's at ISO 1600 and about the same as the 5D3 at ISO 3200.  But with the D800e at ISO 1600 you would have 1 stop better DR than the 5D3 at 3200, and similar SNR.

Once you realize that Exposure is all about getting the most photons possible given your technical/artistic constraints, and ISO is an independent variable about processing those photons iinto a raw file while maximizing SNR and DR without clipping desirable highlights you are on your way.  Give it a try and let us know if it works for you.

Jack

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Per Baekgaard
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Re: D800E night sky shots: Fabulous. ISO?
In reply to Jack Hogan, 11 months ago

Jack Hogan wrote:

[...] Not a problem, you can correct brightness to your delight in the raw converter without a SNR penalty, per my previous post.

Jack, which raw converter do you suggest for this use ("clean" ISO boost in PP).

- Per.

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Astrophotographer 10
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Re: D800E night sky shots: Fabulous. ISO?
In reply to Jack Hogan, 11 months ago

Thanks Jack for the very thoughtful and fabulous advice. I will certainly be implementing your suggestions.

Greg.

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Jack Hogan
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Re: D800E night sky shots: Fabulous. ISO?
In reply to Per Baekgaard, 11 months ago

Per Baekgaard wrote:

Jack Hogan wrote:

[...] Not a problem, you can correct brightness to your delight in the raw converter without a SNR penalty, per my previous post.

Jack, which raw converter do you suggest for this use ("clean" ISO boost in PP).

Hi Per,

If you find undesirable hue twists  or other raw-converter introduced artifacts at high ISOs I understand that RawTherapee  with the 'neutral' profile is as 'clean' as it gets, and it lets you correct up to 10 stops.  It also lets you choose demosaicing algorithm, which may come in handy in certain difficult situations, and has pretty good sharpening/denoising.  It also does flat fielding (don't know about stacking).

I suggest trying a few with your intended image type to see what works for you.  You may not notice or you might like the non-neutral rendition.  Most are fine with linear brightness increases (+EC) of a few stops so I wouldn't worry about it.  I use CNX2 and if I need more than the 2EV compensation it allows I use an LCH step in Master Lightness mode - but I don't do astrophotogaphy, yet so I do not know if that's a good way to go in that case.

Jack

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Per Baekgaard
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Re: D800E night sky shots: Fabulous. ISO?
In reply to Jack Hogan, 11 months ago

Jack Hogan wrote:

[...]

I understand that RawTherapee  with the 'neutral' profile is as 'clean' as it gets, and it lets you correct up to 10 stops.

Great tip -- especially as I'm doing most of my (non-photo) related work in a Linux environment where RT also works well. Hadn't thought about that for this application. Thanks!

[...]  I use CNX2 and if I need more than the 2EV compensation it allows I use an LCH step in Master Lightness mode

I'm normally using LR for most of my work, but have and use CNX2 from time to time as well. Haven't done too much astronomy work with CNX2 though, but I'll try the "ISO boost trick" there also -- there is also an option for noise reduction that tries to take care of stars in CNX2, which might also help some.

Thanks!

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