Crux w/ DSLR: lots of detail but almost no colour (?)

[Camelopardalis (Dunk)]

Originally Posted by janoskiss

Yeah sure once you're above a certain threshold. But only then; as you were implying with your "broken record" comment. Otherwise we would not need tracking. We'd just take short snaps, or a video even of deep sky and stack like mad, like panetary imagers do.

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@Camelo yeah I know about Gimp 2.9 and I have the sources sitting on my computer, but the dependencies for compiling it on my current system are a pain I'm yet to be prepared to deal with. I'm quietly hoping Gimp folk will finaly release a stable 2.9 version (at long last: it's been 10+ years wait for more-than-8-bit-colour support).

Yes and no...if the noise has higher values than the background sky (underexposed) then you can still stack a lot of subs and reduce the noise, it just takes more subs. The noise reduces with the square root of the number of subs, whereas the signal is additive. Exposed optimally, the noise is swamped by the values of the background sky.

Just to blur the boundaries, lookup lucky imaging...it's basically where small sensors suitable for planetary imaging (high sensitivity, very low read noise) are being used with fast scopes and taking lots (thousands) of short exposures and getting some really interesting results with DSOs

For testing GIMP development, look into virtualisation platforms such as Virtual Box, VMware Player or similar. You can then install one of the more cutting-edge distributions into the virtual machine, with all its dependencies, without messing up your running system

[janoskiss (Steve H)]

Originally Posted by Camelopardalis

Yes and no...if the noise has higher values than the background sky (underexposed) then you can still stack a lot of subs and reduce the noise, it just takes more subs. The noise reduces with the square root of the number of subs, whereas the signal is additive.

Assuming the noise is completely random and independent of the signal, yes. Thank you Central Limit Theorem (what a gem of a theorem!). But there is a garbage-in = garbage-out point where it becomes futile to do anything practical with short exposures. But why am I telling you this? You're the one who keeps emphasising the need to expose for long enough to get the background sky above the noise floor.

Just to blur the boundaries, lookup lucky imaging...

I watched a few talks on youtube last night on AP and heard "lucky imaging" mentioned several times. I thought I got the planetary vs deep sky thing but I'll look into it some more. I presume if you have an ultra low- (near no-) noise sensor and enough processing power you could in principle take very short exposures.

The ultimate form of this is a photon count detector, where each "exposure" is just a single photon hitting one detector pixel. For scientific/medical applications there is work under way on detectors that can not only log where and when each photon hits, but the energy of the photon as well (the precise colour). I understand that apart from the energy detection part there are CCDs available that come as close to no-noise as stray light and cosmic rays allow. But for the foreseeable future I'll have to make do with my cheap DSLR and all its inherent shortcomings.

I realise there are ways to get Gimp 2.9 going but unless it comes bundled and ready to go with a bleeding edge distro I don't think I have the time and/or patience to make it work.

I am very impressed with dcraw btw and that it provides direct access to each raw pixel value beneath the Bayer filter.

[Camelopardalis (Dunk)]

Glad to hear you've been listening

While the perfect sensor doesn't exist, a good sensor exhibits read noise that is normally distributed, or thereabouts.

The latest sensors...like the IMX224 (in the ZWO ASI224MC) have <1 e read noise in high conversion gain mode.

Previously I mentioned that another factor in getting good results is to know the equipment and play to its strengths. Regardless of what the read (or thermal) noise behaviour is, once you know what it is you can expose accordingly and overcome it There's a lot of fun, and some pretty amazing results, to be had from inexpensive equipment!