Sharpcap live stacking success but very early diminishing returns problem?

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realflow100 United States of America
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Sharpcap live stacking success but very early diminishing returns problem?

#1

Post by realflow100 »


So far it seems to work
but diminishing returns already at only 10 frames
regardless of exposure time as well. after just 10 frames I have VERY SERIOUS diminishing returns. even 1000 frames more only gets me 1/2 to 1/4 the noise level. or something resembling that.
whether its incredibly short 1/10 shutter speed. or 1 second exposures.
Why do I have diminishing returns so quickly?
do I really need to take 10 times more frames to get "half" the apparent noise
so 100 frames to get half of the noise of when i have 10 frames.
then 1000 frames to get half of that noise.
then 10,000 frames to get half of that noise?
its not nearly this bad when I take full resolution images then stack them the normal way
but i have severe diminishing returns problems in sharpcap with only 10 frames
even when I cranked down the contrast to the lowest in my camera to preserve dynamic range.
Hot pixels are really bad too.
Theres also a weird grid-like pattern to the noise grain. which seems fixed and unchanging
dark frame subtraction doesnt work. Just causes ugly dark colored spots where the hot pixels used to be.

These tests are just done while under cloudy conditions. so no alignment. or dithering.
I'm wondering if natural dithering from untracked on a tripod stacking and aligning would help reduce this strange problem at all?
(about 20 to 50 frames between re-position the target by hand or so)
1 second exposures at 50mm F1.8 on a canon SL1/100D is what I'm aiming for.
Svbony SV503 70mm ED F6 420mm FL refractor telescope (New)
Canon EOS 100D/SL1
Tamron 18-200mm F3.5-F6.3 II VC lens
canon 50mm STM F1.8
svbony 8-24mm zoom eyepiece
svbony goldline 66 degree 9mm and 6mm + 40mm plossl + 2x barlow.
svbony UHC 1.25 filter + astromania 1.25" O-3 filter + also an svbony H-B filter.
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realflow100 United States of America
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Re: Sharpcap live stacking success but very early diminishing returns problem?

#2

Post by realflow100 »


Theres barely any difference between 50 frames and 3500 frames
What is going on?
Svbony SV503 70mm ED F6 420mm FL refractor telescope (New)
Canon EOS 100D/SL1
Tamron 18-200mm F3.5-F6.3 II VC lens
canon 50mm STM F1.8
svbony 8-24mm zoom eyepiece
svbony goldline 66 degree 9mm and 6mm + 40mm plossl + 2x barlow.
svbony UHC 1.25 filter + astromania 1.25" O-3 filter + also an svbony H-B filter.
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starfield United States of America
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Re: Sharpcap live stacking success but very early diminishing returns problem?

#3

Post by starfield »


Hi realflow,

Your SNR noise ratio doesn't decrease in a linear manner. SNR is a function of your signal divided by the square root of your noise. For a better explanaiton than I can do, check out this video from Craig Stark. Good explaination of how this works. Checkout the explanation around minute 8. https://youtu.be/EO4QFb3ydNM
Scopes: Esprit 100, 12.5" Telekit Dob
Camera: 294 MC Pro, 224 mc, 2600mm
Guiding: ZWO 290 mini on 120mm guide scope
Mounts: EQ6R-Pro, EQ Platform.
Filters: Optolong L-Pro & L-Enhance, Chroma 36mm LRGB, 5nm HA, 3nm OIII, 3nm SII.
Software: SharpCap, SGP, StarTools 1.7, Photoshop, Pixinsight
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AstroBee United States of America
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Re: Sharpcap live stacking success but very early diminishing returns problem?

#4

Post by AstroBee »


It's always been my understanding that dithering helps reduce SNR. I hope that's true as I've always dithered, even in SharpCap since Dr. glover enacted the dithering feature in SharpCapPro.
With what sounds like these really short exposures that you are doing, you are probably not collecting enough photons to swamp the read noise of your sensor.
Greg M.~ "Ad Astra per Aspera"
Scopes: Celestron EdgeHD14", Explore Scientific ED152CF & ED127 APO's, StellarVue SV70T, Classic Orange-Tube C-8, Lunt 80mm Ha double-stack solar scope.
Mounts: Astro-Physics Mach One, iOptron CEM70EC Mount, iOptron ZEQ25 Mount.
Cameras: ZWO ASI2600mm Pro, ZWO 2600MC Pro, ZWO ASI1600mm
Filters: 36mm Chroma LRGB & 3nm Ha, OIII, SII, L-Pro, L-eXtreme
Eyepieces: 27mm TeleVue Panoptic, 4mm TeleVue Radian, Explore Scientific 82° 30mm, 6.7mm , Baader 13mm Hyperion, Explore Scientific 70° 10mm, 15mm, 20mm, Meade 8.8mm UWA
Software: N.I.N.A., SharpCapPro, PixInsight, PhotoShop CC, Phd2, Stellarium
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