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gquinzi
super member
Reged: 10/26/07
Posts: 151
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Okay well maybe not too dumb but here goes...
You're all set up and the rig is firing off say... 120 min x 60s exposures. Now, with each and every consecutive exposure per minute, are we receiving different photons with each minute that goes by or... Are we receiving the same photons over and over thus amplifying the detail in the final image once those exposures are stacked? I know the more shots you average together the more your signal increases while the noise gradually decreases. I guess what I am really trying to figure out is... With consecutive 60sec exposures are we simply sampling the same light over and over or are we recording different parts of that light as the photons fall onto our sensors?
I’m guessing with 10 exposures @ 60 seconds stacked would equal one single 10 minute exposure (albeit may be noisy depending on temp.)
I'm beatin myself up thinking about this  Sorry if this seems confusing to anyone reading this post. 
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Orion 80ED w/ WO .8X FF and WO focuser upgrade
ST-80
Meade 8" SCT
F6.3 F/R
LXD75 Hypertuned w/Star patch GPS
Baader modified Canon 350D
DSI Pro
PHD Guiding
DSLR Shutter
Orion Dynamo Pro 17 (power tank)
A couple o' Naglers
A couple o' generic plossl's
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ChazK
Pooh-Bah
Reged: 11/23/05
Posts: 1453
Loc: Melbourne, Florida
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Remember a photon is a quantum of light energy. It is a discreet particle. Each photon hits your chip and activates the photodiode on the CMOS or CCD surface and it only gets more interesting from there. So each exposure is of different particles streaming into your telescope.
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Tak TOA 130mm/NJP Temma2
Tak FS 60CB
Canon 40D (unmodded)
Canon EF 28-135mm f/3.5-5.6
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gquinzi
super member
Reged: 10/26/07
Posts: 151
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So there it is...much clearer to me now. Thanks a bunch for the response.
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Orion 80ED w/ WO .8X FF and WO focuser upgrade
ST-80
Meade 8" SCT
F6.3 F/R
LXD75 Hypertuned w/Star patch GPS
Baader modified Canon 350D
DSI Pro
PHD Guiding
DSLR Shutter
Orion Dynamo Pro 17 (power tank)
A couple o' Naglers
A couple o' generic plossl's
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D. Perry
member
Reged: 09/28/07
Posts: 50
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And just a small clarification... as your camera collects more light, the noise does not go down. The signal increases more rapidly than the noise. Therefore, the signal to noise ratio becomes greater, in favor of signal. Also, remember that noise is the dark and uncertain areas in the camera's FOV, not to be confused with the thermal signal coming from the sensor itself. Neither of which are to be confused with the read noise. 
Best,
dp
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Daniel Perry
www.californiastars.net
Ontario, California [ 34N | 117W ]
• Astro-Physics 900GTO & ATS Portable Pier
• Meade 12" LX200-ACF OTA
• Celestron 9.25" SCT
• Takahashi FSQ-106ED
• Stellarvue SV80S (Lomo super APO triplet)
• SBIG ST-10XME
• Canon EOS 5D MII (unmodified)
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PhilHoyle
super member
Reged: 09/02/06
Posts: 141
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Quote:
I’m guessing with 10 exposures @ 60 seconds stacked would equal one single 10 minute exposure (albeit may be noisy depending on temp.)
Nope. Not exactly. The signal to noise ratio will increase linearly with the amount of time allowed in the sub-exposure. It will increase by the square root of the number of sub-exposures. So...basically if you increase your sub-exposure from 1 minute to 2 minutes, you double your signal to noise ratio. If you stack 2 1-minute subs, you increase your signal to noise ratio by 1.4.
The stacking process helps "remove" the random part of the noise. I have "remove" in quotes here because it doesn't really remove it, it just smooths it out so that we can adjust the dark part of the image to get rid of it later. The more sub images we have, the smoother it gets. This allows us to brighten the dark parts of the image in processing to a greater extent before the noise becomes objectionable.
It is usually better to take longer subs, within other practical limits, to get a better signal to noise ratio and then we don't have to stretch the image so much in processing.
There are other sources of noise in images that are not random. These are removed with flats and dark frames etc.
Phil
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ChazK
Pooh-Bah
Reged: 11/23/05
Posts: 1453
Loc: Melbourne, Florida
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Phil,
Thanks...that answered a question of mine!
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Tak TOA 130mm/NJP Temma2
Tak FS 60CB
Canon 40D (unmodded)
Canon EF 28-135mm f/3.5-5.6
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Galaxy001
Carpal Tunnel
Reged: 06/08/06
Posts: 1633
Loc: San Ramon, California
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I've certainly been educated as well. Phil, thanks for the mathematical relationship, that certainly puts it into better perspective (for me at least).
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Zach
Remember to Keep Looking Up!
My observatory:
 Meade LX90 GPS 8" UHTC
With a (Meade) 18 mm UWA ep and a 3x telextender
Other cool stuff:
Meade ETX-60
DSI Pro
60 mm Solar Filter
Celestron dew shield
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gquinzi
super member
Reged: 10/26/07
Posts: 151
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Thanks to all who've replied. I too have learned a great deal. When it comes to exposures, settings and techniques sure one could mimic others but personally I've always found it helps to know how and why they work. Of course the fact I married a scientist makes it worse. 
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Orion 80ED w/ WO .8X FF and WO focuser upgrade
ST-80
Meade 8" SCT
F6.3 F/R
LXD75 Hypertuned w/Star patch GPS
Baader modified Canon 350D
DSI Pro
PHD Guiding
DSLR Shutter
Orion Dynamo Pro 17 (power tank)
A couple o' Naglers
A couple o' generic plossl's
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Luc Coiffier
sage
Reged: 03/18/06
Posts: 281
Loc: Grenoble, France
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Quote:
I’m guessing with 10 exposures @ 60 seconds stacked would equal one single 10 minute exposure (albeit may be noisy depending on temp.)
You will have the same SNR but not the same signal.
For example, if you are imaging a faint target that is sending a photon every 10 minutes, you will have it on only 1 of your 60 second images and it will be considered as noise.
On the other hand it will be on all your 10 minute images and will be considered as signal.
Luc
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SW 254/1200, EQ6 mod. Rajiva
Canon EOS 350D (mod Baader)+MPCC
http://deepskystacker.free.fr
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