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  #21  
Old 15-10-2017, 07:07 PM
kens (Ken)
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ZWO is moving towards having offset fixed at 50 in the driver (the value currently used at gain 300). This is to simplify things and make it easier to integrate with tools like SGP. It makes an insignificant difference to dynamic range. I've started using offset 50 and making darks accordingly.
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  #22  
Old 15-10-2017, 07:25 PM
dpastern (Dave Pastern)
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Yeah, I just have been reading that Ken on the pro thread that Jon started.
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  #23  
Old 15-10-2017, 07:27 PM
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Yeah, Jon [Rista] over at CN has argued pretty much the same - keep subs short, and lots of them, and don't go ballistic with the bias/offset. I personally think you're bias/offset settings are too high and you would do better to drop them.
Thanks. May be the case. Still experimenting as just got the camera last month.

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Does well depth change with gain or does increasing gain just increase the rate that you fill the well?
Well depth will stay the same, but the counter will overflow sooner with increasing gain! i.e. at the gain I was using, I think it is about 0.5 e per 16 bit chunk of ADU, so 32 ADU per electron. Hence only 2048 electrons can be counted before it saturates, even though I think the wells are 20000 electrons or so.

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What bias/offset settings are you using?
I was, for that, using gain 202 and offset I think 50. The higher gain was to get a lower read noise.

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I haven't bought my ZWO 1600 - yet. I'm gonna start with 100/21 and see how things go when I do get it. A friend on YouTube shoots @ 139/21 from memory and gets great results too. From my understanding, you get no real gain from bumping up the gain (no pun intended!) - it's far better to preserve SNR.
Yeah. I think as long as you're sky limited then unity gain (139) is fine. But at unity gain narrowband subs need to be quite long to be sky limited. Even at the gain I was using, I think it would be something like 14 minutes. I was only shooting 10 min subs.

For normal luminance on the other hand, at gain 139 I get sky limited subs in under 60 seconds.
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  #24  
Old 15-10-2017, 07:42 PM
dpastern (Dave Pastern)
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well that's interesting Paul. I'm duly taking notes :-) thanks for the thoughts.
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  #25  
Old 15-10-2017, 07:53 PM
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well that's interesting Paul. I'm duly taking notes :-) thanks for the thoughts.
No worries. Of course I may be talking nonsense as I'm learning about this camera as I go
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  #26  
Old 15-10-2017, 09:08 PM
dpastern (Dave Pastern)
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No worries. Of course I may be talking nonsense as I'm learning about this camera as I go
nah. All input is valid imho. Take all the information in and then apply it to gain experience. At least, that's what I intend to do. The ZWO will be my first astro imaging camera, and I'm very new to it all (I did a tiny, tiny, tiny bit of imaging with my DSLR 8 or so years ago before I got frustrated and lost interest). This time, I'm making an effort to educate myself, so that problems don't frustrate me and I progress in the hobby. Diving into things feet first is never a good idea!!!!!!!
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  #27  
Old 15-10-2017, 09:36 PM
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nah. All input is valid imho. Take all the information in and then apply it to gain experience. At least, that's what I intend to do. The ZWO will be my first astro imaging camera, and I'm very new to it all (I did a tiny, tiny, tiny bit of imaging with my DSLR 8 or so years ago before I got frustrated and lost interest). This time, I'm making an effort to educate myself, so that problems don't frustrate me and I progress in the hobby. Diving into things feet first is never a good idea!!!!!!!
Great. I'm sure you'll enjoy the camera!
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  #28  
Old 15-10-2017, 09:46 PM
dpastern (Dave Pastern)
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Great. I'm sure you'll enjoy the camera!
Still so much to learn...I have to master polar alignment (have a QHY polemaster on the way from Theo @ gamma), and I've never used a guiding setup before either, so will need to investigate and figure out how to use PHPguide2 and eqmod as well (haven't used that either). The mount has been in storage for 8 years, so it's prolly seized up and won't work knowing my luck lol. I have only myself to blame. Just looking at the rowan astronomy belt mod, but can't really determine if it's worth it or not. I cannot afford a new mount there's a beautiful used AP1200 up on astromart that I'd love to get, but I just don't have the money for it (well, I do, but that money is spoken for sadly). I just don't have much faith in the eq6pro! But, if I can get polar alignment nailed and figure out guiding, short 2-3 min subs should be AOK and the mount should suffice, especially with a light load such as my new esprit 80 triplet. Well, that's the plan.
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  #29  
Old 15-10-2017, 11:15 PM
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Quote:
Originally Posted by dpastern View Post
Yeah, Jon [Rista] over at CN has argued pretty much the same - keep subs short, and lots of them, and don't go ballistic with the bias/offset. I personally think you're bias/offset settings are too high and you would do better to drop them.
I disagree - I'd say the offset is too low, but that is based solely on the values I see with my camera, each sensor is different. At unity gain, I use an offset of 37.

If you drop the offset too low, you risk not being able to calibrate your images properly, since you're clipping the bias off the left hand edge of the histogram.

I saw some discussion over there about the new cameras and them having fixed offset (of 50), so this is likely a moot point in the near future.
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  #30  
Old 15-10-2017, 11:22 PM
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Camelopardalis (Dunk)
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No worries. Of course I may be talking nonsense as I'm learning about this camera as I go
Isn't that half the fun
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  #31  
Old 16-10-2017, 12:27 AM
dpastern (Dave Pastern)
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Originally Posted by Camelopardalis View Post
I disagree - I'd say the offset is too low, but that is based solely on the values I see with my camera, each sensor is different. At unity gain, I use an offset of 37.

If you drop the offset too low, you risk not being able to calibrate your images properly, since you're clipping the bias off the left hand edge of the histogram.

I saw some discussion over there about the new cameras and them having fixed offset (of 50), so this is likely a moot point in the near future.
yes, I saw that too with the 1600 pro having it set to 50, with minimal impact on the image. I came to my own conclusion after having a read of http://www.stark-labs.com/help/blog/...nAndOffset.php. Of course, I may have misunderstood things wrong, or miscalculated them too. As I said, i'm a noob!
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  #32  
Old 16-10-2017, 07:58 PM
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If you watch some of Craig Starks videos, he says he's basically lazy and doesn't bother calibrating any of his images...
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