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By StarGazingSiouxsie
Hi,
I have just purchased a couple of these https://www.celestron.com/products/powertank-lithium-pro
The manual says that when the battery is powering something that the 4 red battery will blink in sequence to show that power is flowing. My units are fully charged up, yet when I use them the red lights don't blink in sequence. I just have 2 red static lights lit under the 4 red battery lights.
I have 2 of the smaller power tanks, the next model down, and the blue battery lights on those do blink in sequence when they are powering an object.
I have tested my new units and they do seem to be providing power. But, if you have one of these, could you confirm please that your red lights don't flash when powering something?
Thanks. It's just that the manual is very specfic about this. (I have double checked and the manual is specific to my new units) Still, it's a Celestron manual so maybe my expectations are too high
Thank you
Siouxsie
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By han59
Probably an old discussion but lets review it with some measurements:
The dark noise should only have a small influence on the total noise of the final image. Most noise is generated by the sky background. Under good conditions SQM = 20.4, I measure using my ASI1600MM-Cool the following noise (standard deviation) in a dark and in a light for an area where no stars are visible (local measurement using ASTAP):
Dark 1 x 200sec, σ = 15 (range 0..65535)
Light 1 x 200sec, σ = 130
The noise in the dark is roughly 12% of the light, which seems acceptable to me. That would argue for about the same amount of darks as lights. With a worse SQM, you can probably do 2.5 times less darks for each (magnitude) step. So under light polluted sky you can do with much less darks than lights.
If you are going to photograph with the H-alpha filter, it will be super dark. In a single H-alpha (7nm) light I measure a σ = 25r. Of these, 15 are self-noise and 10 of the incoming light. In good conditions and using an H-alpha filter, this is an argument to make much more darks than lights
Above for a monochrome camera. To measure with an OSC (color) sensor I think it is better to first split the 4 Bayer pixels into 4 files and then measure them separately.
Some measurements with my ASI1600MM-Cool, monochrome:
DARKS noise:
1 x 200 seconds, σ = 16
1 x 200 seconds - master dark, σ = 15
4 x 200 seconds combined - master dark, σ = 6.8 This is approximately 15 / square root (4)
41 x 200 seconds combined, σ = 5
90 x 200 seconds combined, σ = 3.8 This is a limit value that arises mainly from unevenness of the pixels. The noise will be smaller, approximately 15 / square root (90) is 1.6
STACKED LIGHTS noise (lights corrected with darks and flats):
11x200 seconds, σ = 70 (measured at a star free area, standard deviation in 0..65535 range, sky conditions could have been different)
18x200 seconds, σ = 36
18x200 seconds, σ = 40
40x200 seconds, σ = 26
42x200 seconds, σ = 30
44x200 seconds, σ = 25
58x200 seconds, σ = 20
95x200 seconds, σ = 16
Apparently the light noise decreases considerably while stacking more lights and I reach σ values up to 16 a 20. You do not want to stack these images with a single dark having a σ = 15. If you want to keep the dark noise added below 10% of σ = 16 then you need 100 darks because they give: 15 / square root (100) = 1.5 noise.
So this confirms for a good suburban site (SQM=20.4) you will need about the same amount (or more) darks then lights. For a more light polluted area you can take less darks since the noise from the skybackground will be abundant. For H-alpha work you better take more darks then lights.
Han
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By Xilman
At long last I have managed to image Caliban, also known as Uranus XVI. It is a small (circa 72km) outer satellite of Uranus which was discovered in September 1997 using the Hale 5m telescope at Palomar. Incidentally, Sycorax (U-XVII)was discovered in the same observing session. That satellite is around 1.7 magnitude brighter and so much easier to observe.
Although a three hours exposure, unfiltered for maximum sensitivity, was used the signal to noise ratio is barely 3 and serious image processing was needed to produce a relatively clear image. Even so, it is not especially obvious. The reason is that the MPOC ephemeris predicts that the satellite has a magnitude of 22.2 at the time of observation. More information is available at http://www.astropalma.com/Projects/Satellites/caliban.html
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By Willieghillie88
Hi all,
My friend and I were outside last night looking at the sky and looking for satellites. We saw a few of what I assume were satellites (flat unblinking steadily moving lights) One of them which crossed the sky East to West emitted 2 incredibly bright and intense, very large flashes of pure white light, spaced maybe 2 minutes apart from each other. Neither of us have any more than a basic school knowledge of astronomy but are both interested. We wondered if anyone on here could help shed any light on the flashing satellite we saw?
Many thanks for your time.
Iain
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