GazAstro Posted February 28, 2021 Share Posted February 28, 2021 (edited) Hi all, I'm sure I've read this before somewhere but still unsure of the theory ... Am I correct in thinking that when stacking, 1 to 2 Half's the noise, then 2 to 4 Half's again, then 4 to 8 ... 8 to 16 etc. So going past 16 really needs a massive investment in time ? Also where does sub length come into this ? I use a ZWO 1600 pro and seem to get good results in my bortle 7 / 8 zone with 300 seconds at unity gain. Also, now sure that (as I've been told but wanted to see for myself 😉) that only Ha cuts through the Moon glow. Due to time restraints I've been aiming for an hour per filter but this equates to 12 subs so I guess I need to grab an extra 4 to see the benefit ? For completeness and a recap ... 300 seconds / gain 139 / ZWO 1600 pro / f4.9 ZWO narrowband filters. Edited February 28, 2021 by GazAstro Quote Link to comment Share on other sites More sharing options...
AstronomyUkraine Posted February 28, 2021 Share Posted February 28, 2021 (edited) 5 hours ago, GazAstro said: Hi all, I'm sure I've read this before somewhere but still unsure of the theory ... Am I correct in thinking that when stacking, 1 to 2 Half's the noise, then 2 to 4 Half's again, then 4 to 8 ... 8 to 16 etc. So going past 16 really needs a massive investment in time ? Also where does sub length come into this ? I use a ZWO 1600 pro and seem to get good results in my bortle 7 / 8 zone with 300 seconds at unity gain. Also, now sure that (as I've been told but wanted to see for myself 😉) that only Ha cuts through the Moon glow. Due to time restraints I've been aiming for an hour per filter but this equates to 12 subs so I guess I need to grab an extra 4 to see the benefit ? For completeness and a recap ... 300 seconds / gain 139 / ZWO 1600 pro / f4.9 ZWO narrowband filters. SNR is the goal. The more images stacked, the more SNR we will have in the end result. The simple number to remember is square root. 4 images stacked will have twice the SNR as one image. 16 images stacked will have 4 times the SNR of one image, and so on. Below are 4 images. From the top down is a single image, followed by stacks of 4, 16 and 64. The SNR gets progressively stronger, reducing the amount of noise. The final image stack of 64, will have 8 times the SNR of a single image. I'm not saying you need to take 64 images for each filter, but too many is better than not enough. I stack my images as they come in, then check each hourly stack. I usually find 5 hours is the minimum on each narrowband filter with my1600, and normally go for 10 hours on each filter, if the object has weak signal. Edited February 28, 2021 by AstronomyUkraine 1 Quote Link to comment Share on other sites More sharing options...
GazAstro Posted February 28, 2021 Author Share Posted February 28, 2021 Appreciate the answer though it would take me months to get that much data 😲 I'll aim for 16 subs on each filter moving forward with the option to add data in time. Quote Link to comment Share on other sites More sharing options...
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