Re: [APML]new technique?

[swalters@att.net]

Hi Tony,

Like so many others you've produced, that's a great 
image! 

I expect your note will generate some discussion. About 
a year ago, there was a lot of discussion here about the 
benefits of stacking with a lot of different opinions 
expressed. Someone (Ben MacDaniel?) contacted David 
Malin and after a lot of debate, the conclusion (IIRC) 
was that stacking only reduced noise due to film grain. 

This conclusion has always bothered me a bit. 

It's true that stacking does NOT reduce the effects of 
light pollution since that's as much a "signal" as the 
object being photographed and accumulates linearly in 
stacked images just as the object does. But film grain 
effects, being random, do not accumulate linearly so the 
signal-to-noise ratio (SNR) increases as more images are 
stacked. So, if nothing else were in play, stacking 
would only reduce film grain effects. It does not help 
reduce the effects light pollution at all.

However, there are at least two other noise sources, 
seeing and guiding, that I don't recall being discussed 
then. These are both random effects that I think would 
behave as noise when stacking. Even with excellent 
seeing and excellent guiding, there is still a small 
random effect that these contribute to the image. So 
stacking would help reduce the effects of these 
impairments just as it reduces the effects of grain. I 
think your image confirms this.

So, I think:

1. Signal is Object + Skyglow
2. Noise is Grain + Seeing + Guiding
3. Stacking will improve the SNR so the effects of 
grain, seeing and guiding are less.

Anyway, I do not have the level of experience that you 
and many others on this list have so I am humbly putting 
this forward as a question, not a conclusion.

Whaddayatink?

Steve...

--
http://Astrophoto.home.att.net	
		
> Hello all,
> 
>      Just by accident I have sort of stumbled into a new technique, although it 
> is really more an extension of an old technique...
> 
>       I tried combining nine (9) negatives of m33 ... we masochists need help, I 
> know... but the smoothness of the final image is amazing. Again it was done in 
> groups of three in PW and then those three were combined into one. A lot of 
> these negatives were marginal at best, being the result of "experiments" with 
> exposure times and hypering of the Royal Gold 200. It is now clear that 6 
> negatives is adequate to achieve the signal to noise ratio that I am after... 
> the results are so good I am not going to go the CCD route... 
> I printed the AE Auriga image to 16 X 20 (made from 5 negs) and it is almost 
> grainless and sharp. 
>       This "technique" escaped me in the past because going"portable" you would 
> never shoot 6 negatives of the same thing....but having an observatory changes 
> all that.
> The important thing is that CCD images might be a tad sharper and might work 
> better on tiny things, but this technique creates images that have an intrinsic 
> beauty all their own. With correctly hypered RG200 I think I can carry film a 
> step further by utilizing a large number of originals.
> 
>     I posted the result of all this madness at:
> 
> http://www.astrophoto.com/M33new.htm 
> 
>     I cropped in a bit to see the detail.
> 
>     Have a good one,
> 
>         Tony
> 

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