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Old 04-03-2019, 01:13 PM
Startrek (Martin)
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First time Dithering

Last night whilst imaging the Southern Pinwheel Galaxy I tried dithering for the very first time
I was Dithering each 4 minute sub using BYEOS and PHD2 ( Spiral )
I found each Dither to be different , some would be quick with little affect on guiding whilst others would kick the guiding around pretty severe
I was guiding around 1 arc sec
It it normal to have dithers that do almost nothing and others that shake up your guiding pretty bad eg 1 arc sec up to 1.9 arc sec
I noticed after a big Dither the guiding took almost 2 minutes to calm down to something close to where it was prior but not to the same level
My settings in BYEOS were -
Dither Aggressiveness was 2 or low
Settle Dither was 0.35 for average guiding
Calm down was 20 seconds which didnít do anything on the big dithers as they took 2 minutes
Appreciate any advice or whether the above is normal for dithering
Cheers
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Old 04-03-2019, 01:24 PM
glend (Glen)
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I have noticed that the amount of time required to settle after a dither can be due to rig balance issues. Understanding how your mount behaves best, and how you apply weight, can help reduce settlement time.
Secondly, it may be un-necessary to dither on every sub. My experience suggests that a fair amount of time can be wasted in the dithering and settlement process - for little gain. I would suggest you try reducing the frequency of the dithering as an experiment.
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Old 04-03-2019, 02:43 PM
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The_bluester (Paul)
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Could some of the dithers be taking a long time to settle down due to dec backlash? I tend to balance my setup a little heavy on the camera end (SCT) to try to keep the dec worm in mesh. I also needed to adjust the worm engagement, using the guiding assistant at the start PHD suggested a 2400ms (2.4 seconds) dec backlash compensation time, which I thought to be huge. With tweaks I got that down to about 400ms without any noticeable impact on how the mount moves when guiding, so it obviously leaves enough lash that the worm is not binding anywhere.

How does BYE manage dithers? I never went all that far with it as the old Canon DLSR I was using did not support bulb over USB so I never tried very hard by way of integrating everything. APT requests a dither then monitors the guide star distance to the lock point to decide when it is completed and settled back in to guiding. Does BYE just request the dither and then wait a specified time?

The setup I am trying at the moment (I am trying a number of different workflows) is to set up an image plan with for instance 6 different length exposures in series before repeating it from the start. That way I can dither after the sisth frame and if I progressively stack images (Dark subtraction and stack 30 second images, darks and stack the 60 seconds, then the 120s etc) then finally stack the series of stacked images together, I end up with stacks of same exposure images, which have all had a dither applied since the last one of that time. From memory you can do similar with BYE, set up a line for each exposure time you want then set it to loop the entire plan?
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Old 04-03-2019, 05:17 PM
Startrek (Martin)
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Yes I have a bit of dec backlash in my HEQ5
PHD2 does the Dither , BYEOS just sends the parameters for recommencement of the capture plan
Iíve started stacking and a bit of processing and already I can see a far less noisier image straight off the bat
I did Dither each image so next time I will try every 2nd or 3rd like Glen mentioned
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