Longer or shorter exposures with these warm summer nights?

[ollypenrice]

Indeed, Stuart. I don't knock theory either but I do point out that it must be confirmed - or at least not disproved - by observation. Theory and observation are not opponents; observation is a part of theory. It if isn't then the 'theory' in question is merely an hypothesis.

Olly

[Earl]

The big problem with theory is in reality it is impossible to test in the field as the variables change all the time, lab based experiments are good for in the lab where controlled environments can be achived.

However the controlled lab can provide a very good set of parameters to work with, understanding these and how they work can only benefit work in the field.

[Epicycle]

As it often happens when a natural questions is posed (are 10x1m subs=1x10m subs?), the topic drifts to something more philosophic/interesting like

theory vs experiment. I think the question in the thread is not going to go away and should not be dismissed even though it is tedious for someome with more experience: it's natural for a beginner; I did wonder about it for a while and tried my own experiments. The motivation is very strong: if true you can do without guiding, expensive mounts etc etc (imagine ap-life without a PhD graph? Oh, boy the thought is unbearable).

I like Paul's example of GR, however one can give many other examples some others closer to our experience as amateurs: how about Halley's prediction that his comet had a short period of 75 years? This was based on Newton's powerful math, pure theory... Of course the list is extensive.

The dichotomy expressed here theory vs experiment seems a little narrowminded to me (like looking at the world through one of those 3nm astrodons...): theory is dismissed if it has no connection with reality or does not give a tangible benefit/profit. Oh no! How about the esthetic value of a theory? I would argue that GR is beautiful not matter what. The pursue of esthetic beauty in maths (yes, esthetics plays a big role in creating maths just as in painting or music) often leads to wonderful theories with unexpected connections with reality (functional analysis & quantum mechanics?).

So, if you're an astrophotographer most likely you are in pursue of esthetic values too: you want your pictures to be beautiful, don't deprive theories of them! But yes, keep charlatans (like me) away,

E.

[Shibby]

It's certainly always an interesting discussion... However, you'll notice that nmoushon was not at all questioning whether shorter subs were as good as long subs. His question was about thermal noise with a DSLR and how limiting it can be on your sub length.

Thinking back, my crescent image did indeed have a lot of hot pixels, and I ended up using dark calibration frames which I rarely do. Also, I had taken just enough (17) subs for a sigma stack, which really helps get rid of the thermal noise.

Attached is a crop of one of the RAW subs (click to enlarge), so perhaps people can give opinion on whether this is too noisy or not. The EXIF temperature was 22C (sensor presumably much hotter?)

[Epicycle]

It's certainly always an interesting discussion... However, you'll notice that nmoushon was not at all questioning whether shorter subs were as good as long subs. His question was about thermal noise with a DSLR and how limiting it can be on your sub length.

Yes, that's right, I stand corrected. However, the question 10x1m=1x10m did surface quickly in the thread,

E.

[MartinB]

Have a look here http://www.stark-labs.com/craig/articles/articles.html Go down to 2009 and start with the article "Fishing for photons". If this rocks you boat then continue to the others.

Know the characteristics of you camera and your skyglow. Then you can work out your minimum suitable exposure time. The minimum isn't necessarily the optimum, especially if you have quite a slow downloading camera like me.

I might be talking nonsense but if you want the faintest stuff I think you have to think about the limits of a 16 bit chip. 65000 levels may seem like a lot but if those pixels are only picking up 1-3 photons for a 2 min exposure compared with 1-30 from a 20min one you will have a significant quantitisation error when it comes to doing the stretch. This limitation isn't really about noise.

[Physicist13]

Craig's articles are very good and highly reccomended! Surprisingly you can image with just one bit!..but lets not go there

[Earl]

Yes, that's right, I stand corrected. However, the question 10x1m=1x10m did surface quickly in the thread,

E.

THat is a fair point, and the only way to know it to try it out, it will vary every session with temperature as DSLRs lack the set poitn cooling, so personally in warm weather with DSLR id go for shorter subs than in winter to reduce thermal noise.

[russellhq]

Here's an example of a long exposure in warm conditions with a DSLR (1100D).

This is a shot of the eastern Veil nebula. The average EXIF temperature was 25C (77F). The exposures were taken at ISO100 and were 10mins long. The total exposure time was about 4h30m.

For me, the noise in this image was relatively high which made stretching the faint nebulosity difficult. The end result though is quite pleasing to me.

Hope this helps the discussion along.