Unguided dithering

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mAnKiNd
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Unguided dithering

#1

Post by mAnKiNd »

Hi Robin, me again with more feature requests!

I know it's been requested before (for integration with PHD2), but would it be possible in version 3.2 when you write the sequencer, to implement a checkbox for executing a random unguided ASCOM dither every #frames? This would be akin to what APT and SGPro can do with unguided dithering. Otherwise, a simple script might suffice for this, any takers? I have no clue how to write a script.

With Sharpcap, i've achieved a minimal setup, got rid of my guidescope and guiding program, simplified my workflow, cable runs and overall setup complexity. I use sharpcap from start to finish of my session and never have to open another program during the whole night. The only thing missing for me is that dreaded dither function to help with noise in the stack. If Sharpcap had this feature, it would be the ultimate astrophotography solution for me! I could use APT/SGPro and DSS/Astrotoaster to achieve this, but I'd much rather stick to my preferred workflow with Sharpcap.

Many thanks again and happy holidays!
Minos
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turfpit
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Re: Unguided dithering

#2

Post by turfpit »

Minos

I like the idea of a minimal setup - sat here looking at my ever expanding rats nest of gizmos, cables and extension tubes and trying to achieve simultaneous focus for imaging and guidecam (PHD2) with an OAG :cry: .

"got rid of my guidescope and guiding program" - so how do you guide now or is your mount that good?

All the best for the New Year.

Dave
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Re: Unguided dithering

#3

Post by mAnKiNd »

Hi Dave,

My mount (AVX) can go upto 2 minutes unguided without giving me startrails using my Esprit 80 or even longer using my TSAPO60. I've lately stuck to taking 30 second exposures and then adjusting the gain according to the brightness/dimness of the target, sometimes I go 60 seconds and then adjust gain. Nevertheless, this approach I'm using doesn't require guiding, so I got rid of it altogether and don't fuss around with it anymore and this saves me time and hassle when under the stars. Here's an example from last week:

https://www.astrobin.com/327346/?nc=user

I still dabble in long-exposure astrophotography, and that requires guiding, but not having to collect all those frames (saving hard drive space) and stack them later (love the convenience of stacking while acquiring) and save the stack directly to my OneDrive folder (for backup) just makes a whole lot more sense to me for convinience and I can then just post-process the stack in PI/PS for the final look.

To have a function that dithers when acquiring unguided in Sharpcap would I believe, go a long way to improving the noise in the stack.

Cheers and all the best to you too! :)
Minos
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turfpit
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Re: Unguided dithering

#4

Post by turfpit »

Thanks Minos. AVX mount .... that will be a step up from my CG5 then.

Great image and good approach to using modern CMOS cameras.

This is one of mine (Celestron C8 with an Altair 183C camera) https://www.astrobin.com/327440/?nc=user - 200 x 15s, gain = 6%, unguided. Still a long way to go yet

Dave
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Re: Unguided dithering

#5

Post by mAnKiNd »

That's really nice Dave, got that core and nebulosity with a nice balance! Keep it up and hope that our friend Robin gives us a dithering option soon ;)

Minos
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Re: Unguided dithering

#6

Post by cuivenion »

I'd second this, dithering would also work well with the live sigma stacking I presume.
mAnKiNd
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Re: Unguided dithering

#7

Post by mAnKiNd »

That's exactly the idea, that it would help with noise in a sigma live stack. Also, unguided dithering on the mount via ASCOM should be (not a programming expert) easier to implement in comparison to guided dithering via a client like PHD2/metaguide.

Cheers
Minos
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Re: Unguided dithering

#8

Post by mAnKiNd »

So I've just had a realisation (which I haven't tried out yet) about a functionality in Sharpcap that can serve as an unguided dither!

When I was dithering through PHD2 guiding, i would always select the spiral pattern over the random pattern (no other reason apart from the fact that I like spirals!). I've just made the connection, that in Sharpcap, when connected to your mount, there is a spiral search button! The Sharpcap manual says the following:

"The Spiral Search button (top left of the button group) moves the mount in a growing square spiral around the starting point while it is held down. This is useful when trying to locate an object such as a planet that may be just out of frame. Note that like the movement buttons, the speed of movement of the Spiral Search is governed by the Rate dropdown. If the Spiral Search button is released the spiral movement will stop. Pressing it again will begin a new spiral around the current location – it will not resume the previous spiral pattern."

Now, you can see where I'm going with this: the spiral search function in Sharpcap can serve as an unguided dither!

Currently, there is no way to program this into a sequence but I can see two ways you can currently use the spiral search function to serve as a dither during live stacking:

1) you set the spiral search rate at a high value and you can pause your live stack, tap the spiral search button and initiate a sufficient dither. However, this is no different than using your mounts hand controller to do the same thing.

2) you set the spiral search rate at a low value, click and hold the button and have it continuously drift in a spiral formation. This has to be slow enough for your exposure duration to not cause star trailing, however this might lead to worse noise than without it (think FPN drifting slowly). Now obviously nobody wants to sit there and keep a button pressed all night!!! Windows though, has a clever function called "clicklock" under your mouse settings. It would be possible in theory (will try this asap), to click lock and release your finger off the spiral search button and have it dither spirally for the duration of your live stack. This would however, render you unable to click anything else during live stack acquisition.

There is another possibility, someone with scripting abilities and a kind heart can write us a script to engage the spiral search button every set #frames.

It seems like Sharpcap is already "halfway there" in its ability to perform an unguided dither with its spiral search function, one just needs to script it or program it in.

Any thoughts or takers?

Cheers
Minos
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admin
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Re: Unguided dithering

#9

Post by admin »

Hi,

you could certainly put something together with scripting ... Something like the below gives a rough idea

Code: Select all

# pause live stacking
SharpCap.Transforms.SelectedTransform.FrameProcessor.Parameters.Paused = True

# start mount moving - first parameter is axis (0 or 1), second is rate as multiple of siderial)
SharpCap.Mounts.SelectedMount.MoveAxis(0,1)

# Wait a bit for movement to be big enough
time.sleep(1) # 1s

# Stop moving
SharpCap.Mounts.SelectedMount.Stop()

# Wait a bit for blurred frame to be ignored
time.sleep(30) 

# unpause live stacking
SharpCap.Transforms.SelectedTransform.FrameProcessor.Parameters.Paused = False

That would need to be in a script loop with the direction and size of the movement varying. The spiral movement code isn't really available to scripting, and it also restarts a new spiral every time you release and re-press the button, so doesn't quite do what you want.

cheers,

Robin
mAnKiNd
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Re: Unguided dithering

#10

Post by mAnKiNd »

Robin, thank you so much for your time, seriously! I've read through what you wrote in the script above and that is pretty much an unguided dither command! :)

I know what you mean about the spiral search restarting, but the question is does it always restart in the same direction? e.g. does it always nudge 90° to the right to start the spiral? Or does the spiral restart in random directions? Random would serve well for dithering as every first nudge will be in a new direction. If the first nudge is always starting in the same direction, then the live stack would just drift along with every frame and would show the relevant stacking artifacts at the corners...but if spiral search is not available for scripting, then all this doesn't matter, your approach above for issuing a mount move is a better approach and this is just my chatter because I got a Eureka moment when I realised what Sharpcap's spiral search button can do! :o

You said "...with the direction and size of the movement varying" - this presents a challenge to have some kind of random (or spiral!) number generator ability for the direction and scale min-max range for size? - isn't this basically how guiding programs dither..? The spiral would be a relationship of direction and size, it would follow a Fibonacci sequence?

Cheers to you Robin

p.s. also, if you can write us a script to make the clouds go away, that would be great! You could call it god mode and have a drop down menu to turn it on or off! I think it would go nicely under the preprocessing section :D
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