Dithering

Discussion of using SharpCap for Deep Sky Imaging
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TimothyTim
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Dithering

Post by TimothyTim » Wed Mar 06, 2019 1:03 am

Hello;

I'm not sure if I'm missing something, but I've been having issues with dithering and it's really a nuisance when doing narrowband long exposures. Every time a dither is issued I'm having to lose a frame for it. This is fine when doing 30s-120s exposures losing a frame for the good of the data, but when I'm running 10 minute exposures this can be aggravating... is there a way for SharpCap to pause imaging when dithering between frames? Maybe have it do 5-15 second exposures between dithers and discarding the result.

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Re: Dithering

Post by admin » Wed Mar 06, 2019 8:34 pm

Hi,

At the moment there is no way to stop the frames during the dithering. So SharpCap discards any frames that occur while the dithering is in process. I hope to be able to address this in a future version.

Cheers, Robin

TimothyTim
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Re: Dithering

Post by TimothyTim » Thu Mar 07, 2019 3:41 am

Robin;

Just imagine how much of a pain it is to discard a 10 minute frame because of that and use that as motivation to release that ASAP, thanks :)

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Re: Dithering

Post by admin » Thu Mar 07, 2019 9:46 pm

Hi,

Well I have to admit that 10 minute sub exposures are somewhat longer than I expected people to be using with live stacking!

I wonder if a simple workaround would be to have SharpCap set the exposure down to say 5 seconds during the dinner operation and then set it back to the normal value when the dinner has settled. Most camera brands can treat a change in exposure as a request to cancel any long exposure in progress which should be fine. I would have to make sure that the shorter exposures captured during dithering could not make it into the stack although in an extreme case like yours I expect that if a short exposure did accidentally start being processed for stacking it would simply fail to align because the stars wouldn't be bright enough.

I will think about this one further.

Cheers, Robin

TimothyTim
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Re: Dithering

Post by TimothyTim » Thu Mar 07, 2019 11:34 pm

Robin;

I've been using SharpCap for 10m+ exposures for over 6 months now, your facebook group shared many of my long exposure images.

I think if the dithering function in SharpCap is changed from based on time to based on how many frames at the preset exposure already defined during the live stack, where for example if you are doing live stack with 5 minute exposures, you tell the dithering function to dither once every X frames, and it gives you the ability to specify the settling variable in seconds and that frame is set to be dropped, this would be immensely helpful! I could at that point set for 10 minute exposures telling the system to dither every 4 frames, and would only lose 10-30 seconds instead of 10 minutes. Even if the frame is stacked I would be fine with that since I'm usually deleting the frame during the processing anyways.

poolemarkw
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Re: Dithering

Post by poolemarkw » Mon May 06, 2019 3:42 pm

Hi Robin,

Do you have an idea as to when the Dithering function will be modified to only consume the amount of time required to actually do the dither, rather than consuming the entire frame exposure time?

Thanks,

Mark

AstroNutz
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Re: Dithering

Post by AstroNutz » Sat May 25, 2019 11:36 pm

admin wrote:
Thu Mar 07, 2019 9:46 pm
Hi,

Well I have to admit that 10 minute sub exposures are somewhat longer than I expected people to be using with live stacking!

I wonder if a simple workaround would be to have SharpCap set the exposure down to say 5 seconds during the dinner operation and then set it back to the normal value when the dinner has settled. Most camera brands can treat a change in exposure as a request to cancel any long exposure in progress which should be fine. I would have to make sure that the shorter exposures captured during dithering could not make it into the stack although in an extreme case like yours I expect that if a short exposure did accidentally start being processed for stacking it would simply fail to align because the stars wouldn't be bright enough.

I will think about this one further.

Cheers, Robin
I of course understand that with a lot of time and patience there is a workaround for dithering frame by frame in SharpCap, but I think the point is frankly there shouldn't have to be. In the general "start capture" menu there should be an option to set up dithering control in PHD2 and it should be a simple to use "Dither every X number of frames" and "Settle for X number of seconds" control panel. It shouldn't take but a few days of coding to make this happen, but you will make your users loyal for years to come.

Thank you.
Best,
Alan

vikassahota
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Re: Dithering

Post by vikassahota » Mon Nov 18, 2019 1:08 am

would be good to know if there is any chance of progress on this one, seems left open. Im another that likes to use livestacking with long and short exposures. I've done 10mins and even 30mins exposures (with dithering disabled of course), and I think its a shame it doesnt reconfigure the exposure time as suggested in this thread and minimise the wasted time.
i understand livestack was designed for shorter exposures, but its the only option for dither, and it would work well for long exposures also if this element was improved.

This point and lacking a sequencing option at my two biggest gripes with SC. Was nice to meet Robin at IAS this week, and the sequencing beta looks like its coming together nicely, which is great news for me (mono, filters to switch through the night...).

I'd love to see a solution to this, I really want to dither each frame with those kinds of long exposures, but not by halving the frames harvested per imaging session. We already have quite limited clear skies to cope with... wasting good imaging time, hurts. Better image with half the frames but dithered, or just twice the data.... I had to switch the dither off.
the longer the exposures are, the more painful this is, but even on shorter exposures of few minutes, there is time wasted.
when you are gathering long integration times, eg my last stack of 24hrs... even a 5 or 10% improvement is welcome.

If this was efficient, I think it would even be OK with dithering each frame...say even few-min frames, maybe the cummulative time spent dithering efficiently each frame would still be less than the 3minute dither happening every 4 frames now. And the result would be better.

livestacking or dither during normal capture, shorter or longer exposures, I still think it would be a great improvement to make dither more efficient.

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Re: Dithering

Post by admin » Mon Nov 18, 2019 7:35 pm

Hi,

If you install the very latest update of 3.2 (which is not available via the auto update yet), you will find an extra option in the dithering section that when ticked will cause SharpCap to reduce the exposure to 1 second while the dithering is taking place. The exposure should be put back up to the normal value once the dithering operation has settled.

Cheers, Robin

vikassahota
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Re: Dithering

Post by vikassahota » Tue Nov 19, 2019 2:16 am

Thanks for your quick reply! Happens its clear enough tonite and the 1600m gets first light. I've just enabled that magic checkbox and it works! Im beyond super pleased with this... had disabled dither for 4min exposures, now its back on and doing it efficiently. awesome!!!
thanks Robin!!!!

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