How to cut short a very long exposure? - Script Writing - CHDK Forum
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How to cut short a very long exposure?

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Offline Davo

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How to cut short a very long exposure?
« on: 29 / October / 2022, 10:09:06 »
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I use chdkptp over usb to take long exposure astronomy fotos which are up to 300secs long. First I set the exposure using set_tv96_direct and then shoot. Is there any command that will stop the exposure part ways thru?


Here is my latest shot of Andromeda with my SX530HS.


http://starrydave.com/images/M31%20sx530%20448%2020221028%20st%20asu%20jpg.jpg
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Offline reyalp

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Re: How to cut short a very long exposure?
« Reply #1 on: 29 / October / 2022, 16:19:48 »
Quote from: Davo on 29 / October / 2022, 10:09:06
I use chdkptp over usb to take long exposure astronomy fotos which are up to 300secs long. First I set the exposure using set_tv96_direct and then shoot. Is there any command that will stop the exposure part ways thru?
Nope, not short of turning the cam off or pulling the battery.
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Offline Davo

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Re: How to cut short a very long exposure?
« Reply #2 on: 30 / October / 2022, 07:21:07 »
Thanks for the quick reply. I guess I will have to be more careful before I start the shot. :)
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Offline Mlapse

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Re: How to cut short a very long exposure?
« Reply #3 on: 02 / November / 2022, 17:49:57 »
it would be a different approach, but if you could use an usb remote

https://chdk.fandom.com/wiki/USB_Remote

you could write a script that keeps the lens open for as long as you press the button or f.i. one press to start and one press to stop exposure
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Offline reyalp

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Re: How to cut short a very long exposure?
« Reply #4 on: 02 / November / 2022, 19:29:31 »
Quote from: Mlapse on 02 / November / 2022, 17:49:57
you could write a script that keeps the lens open for as long as you press the button or f.i. one press to start and one press to stop exposure
There is no CHDK functionality to stop an ongoing exposure, regardless of whether you use the remote.

If the Canon firmware has a "bulb" mode, you could control that with key presses (real or scripted, with or without remote), but AFAIK very few cams have that. Maybe just the EOS Ms?

You could also probably close the *shutter* before the exposure was over, but the Canon firmware would continue to run the normal sequence, integrating the sensor for the specified time.
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Offline Mlapse

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Re: How to cut short a very long exposure?
« Reply #5 on: 03 / November / 2022, 06:25:42 »
in the future the g1x III might be added to that list.
but for now i see you nailed it again, not viable for the sx530
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Offline pigeonhill

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Re: How to cut short a very long exposure?
« Reply #6 on: 03 / November / 2022, 13:58:56 »
One thought is to use a multi shot approach, which will likely be a better approach than a taking a single image, ie noise.


In my LBS script the user can specify the time of the integrated exposure, that is based on the set base exposure repeated n times and post processed using statistics, eg [size=78%]https://photography.grayheron.net/2021/10/more-thoughts-on-multiple-image.html[/size]


It would be really easy to interrupt the exposure capture, ie after any simulated time, eg with a button press.


As I say, just a thought.
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Offline Mlapse

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Re: How to cut short a very long exposure?
« Reply #7 on: 03 / November / 2022, 14:12:56 »
that would probably be my favorite way too.
with ccd cams i've done 60 seconds without too much noise, but with cmos i's say that's closer to 20 seconds before i feel it's too much.
it all depends on what you want to accomplish i guess.
and i think the result Davo posted is looking nice, don't know how much post processing was involved.
« Last Edit: 03 / November / 2022, 14:14:38 by Mlapse »
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Offline reyalp

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Re: How to cut short a very long exposure?
« Reply #8 on: 03 / November / 2022, 17:15:07 »
Quote from: pigeonhill on 03 / November / 2022, 13:58:56
One thought is to use a multi shot approach, which will likely be a better approach than a taking a single image, ie noise.
Yes, stacking definitely a viable alternative, though it obviously complicates the workflow.

(here's my take on Andromeda using my fixedint script with g7x, 5040x5s exposures on a fixed tripod. With a tracking mount one would certainly want to use longer subs)
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Offline pigeonhill

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Re: How to cut short a very long exposure?
« Reply #9 on: 03 / November / 2022, 17:36:06 »
Quote

5040x5s exposures on a fixed tripod


Impressive!
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