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Dithering-BYN and PHD2 with DSLR at 25c


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Here in Thailand many imaging sessions happen with ambient around 25c. Imaging with a DSLR, noise is always an issue.

How much image camera dithering seems like a good start? If I use 15 guider pixels, that equals 12 imager pixels, as I'm oversampled a little.

So, my understanding is that dithering aggression  in BYN is multiplied by dither scale in PHD2. For example phd2 at 5.1 and BYN  aggression at 3 would give a dither of 15 guide camera pixels=12 image camera pixels (image scale 1.3" guide scale 1.03) . Correct?

If so, is there any preference as to which number is set higher? Maybe aggression in BYN at 5 and scale in PHD2 at 3?

Would the settle time in BYN vary, maybe with the exposure length in PHD2? I usually set a 10 second pause between sub captures in my sessions.

Not really needing precise settings, just some advise as to what criteria to use.

Thanks--Jack

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  • 2 weeks later...

15 pixels for the imager (not guider) is definitely in the right ballpark. I don't think it matters which settings you use to achieve that, effectively you're just multiplying one number by another to get the same amount of movement.

Settle time is hard to determine by theory. Just experiment by using a really long settle time between two short exposures and monitor your guiding graph to see when it settles, then use that time plus a bit extra as the value for the imaging run. Might be easiest to just time it with a watch rather than trying to convert the graph scale to seconds.

Settle time may well increase with longer guide exposures depending the the guide algorithm, as longer exposures take more time to generate data points for the algorithms to work on.

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Thank very much. I use BYN (BYEOS clone) which controls the dithering through PHD2. So I use dither every 2 frames. I also use a 10 second pause between frames. So is the sequence close shutter, download, pause, dither, settle? I guess what I'm curious about is whether increasing the pause period will help settle? As the dithering  and settling must occur prior to shutter opening again, does that mean that the settle time is like additional pause time in regards to sensor cooling? If I'm happy with 10 secs. of cooling then could I not have say 7 seconds of pause with 3 seconds of settle? If the pause is at the end of the sequence, then that implies I already have 10 seconds of settle time from the pause.

In any case wouldn't it make sense to have the dithering occur right after the downloading?

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Just a note on your settling time - When I was less automated (now use capture software that will start back up once the mount has settled) I used to give the mount 30s to settle. The last thing I wanted was that it hadn't quite settled well and was already onto the next sub.

Can't help with the other bits ...... sounds very complicated :D

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Yes normally dithering is done right after the shutter closes, even during download if the software supports it. It has been a while since is used BYE so not sure of the exact sequence of settings to achieve that, but there is no need to have an extra pause as well as settle time assuming settle time is long enough to settle the guiding.

In terms of temperature control I doubt ten seconds will achieve anything much at all. I have done a fair few tests in respect of dark frames and a Canon and to achieve a stable temperature for darks took a portable fridge plus ice packs and 30 minute pauses between frames! The same would be true with light frames. Your mileage might be a bit different with a Nikon but not fundamentally so.

Read all about my adventures here: http://www.blackwaterskies.co.uk/2015/02/pixinsight-dslr-workflow-part-2a-dark.html

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Yes normally dithering is done right after the shutter closes, even during download if the software supports it. It has been a while since is used BYE so not sure of the exact sequence of settings to achieve that, but there is no need to have an extra pause as well as settle time assuming settle time is long enough to settle the guiding.

In terms of temperature control I doubt ten seconds will achieve anything much at all. I have done a fair few tests in respect of dark frames and a Canon and to achieve a stable temperature for darks took a portable fridge plus ice packs and 30 minute pauses between frames! The same would be true with light frames. Your mileage might be a bit different with a Nikon but not fundamentally so.

Read all about my adventures here: http://www.blackwaterskies.co.uk/2015/02/pixinsight-dslr-workflow-part-2a-dark.html

Very interesting. I had someone else recommend these pauses. I guess it doesn't matter if it's called a pause or settling time. My camera is getting modded right now. When I get back up and running, I'll just watch my graph and time out the time to settle, give it a bit more, and done. Thanks to you and SWAG too.

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