Max recommended duration of video capture to freeze small scale details?

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Max recommended duration of video capture to freeze small scale details?

Post by AJamesB »

Not sure on the rules for linking other forums so I won't link it, but in the cloudynight solar forum someone posted a 30min timelapse of the current sunspot in h-alpha. What amazed me the most was just how much small scale movement and change there was just in a fraction of the duration of the timelapse, both on the larger structures but even more so on the small surface details.

This got me wondering, given all that small scale rapid movement, what the consensus is on the max recommended duration a single video capture should be (that is meant for a single image, not a time lapse) when working at higher resolutions? At times my captures have been up to 3-4 minutes long when using sharpcap's 'seeing monitor function' (only records frames that exceed a user defined sharpness level that is measured in real time), and after seeing just a second or two of that time lapse I'm thinking that's likely way too long to avoid surface movement. Should I be aiming for less than 2 minutes? 1? Less than 30 seconds? Curious what others have come to see in regards to this.

I've also heard that one should have the capture speed at 10ms or less to avoid atmospheric blurring, is that also correct?

Thanks in advance for any input!


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Re: Max recommended duration of video capture to freeze small scale details?

Post by JochenM »

It depends a bit on the fps I'm pulling (depending on which camera is being used). For a slightly slower one like the IMX178 (which is also what you're using, right?) I try to limit my captures to 30-40 seconds tops for the reasons you've mentioned.


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Re: Max recommended duration of video capture to freeze small scale details?

Post by Montana »

Yes, I agree. For timelapse I usually capture 500 frames per avi and click start after it finishes. So at 38 fps 500 frames is achieved in 13 seconds. However as it takes me a bit of time to get the subject back to the reticule point (I don't have a Hinode solar guider) I would say I was taking an avi every 30 seconds for 13 seconds at a time. This is with my Grasshopper 3 (not sure what the exposure is). A lot changes in 1 minute!! I would have 8 frames to use in that 1x 4 minute capture of yours!

Alexandra


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Re: Max recommended duration of video capture to freeze small scale details?

Post by Radon86 »

Hi Guys,

I did not know that you could mark your subject with a reticule ! I will try that next time I have a sunspot or active region/proms to image !
I will also check out the Hinode solar guider, as I thought solar tracking was enough, but I read somewhere that an EQMod controlled mount does not track the sun in Declination, only right ascension.

Thanks Alexandra!

Magnus


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Re: Max recommended duration of video capture to freeze small scale details?

Post by Bruce G »

I think it was Valery who posted an article related to this. I thought I downloaded it, but I can't find it.
In the article, they recommended a maximum of 10 ms for exposure (good news for me, since I was trying to keep the exposure shorter) based on the stability of air pockets and, I believe, video sequences of about 1000 frames, based on the motion of surface features.

I may be remembering this wrong but that's what I'm using these days. With a Lunt 80mm telescope (single stack) and ZWO ASI174MM camera, I can usually set an exposure of a little over 2 ms at a gain of 0 for a full disk with no barlow and 10 ms at a gain around 100 for surface features with a 5x barlow. I find 1000 frame videos much easier to work with than longer ones even though I have to process more of them


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Re: Max recommended duration of video capture to freeze small scale details?

Post by rsfoto »

ammonthenephite wrote: Tue Jun 09, 2020 10:11 am Not sure on the rules for linking other forums so I won't link it, but in the cloudynight solar forum someone posted a 30min timelapse of the current sunspot in h-alpha. What amazed me the most was just how much small scale movement and change there was just in a fraction of the duration of the timelapse, both on the larger structures but even more so on the small surface details.

This got me wondering, given all that small scale rapid movement, what the consensus is on the max recommended duration a single video capture should be (that is meant for a single image, not a time lapse) when working at higher resolutions? At times my captures have been up to 3-4 minutes long when using sharpcap's 'seeing monitor function' (only records frames that exceed a user defined sharpness level that is measured in real time), and after seeing just a second or two of that time lapse I'm thinking that's likely way too long to avoid surface movement. Should I be aiming for less than 2 minutes? 1? Less than 30 seconds? Curious what others have come to see in regards to this.

I've also heard that one should have the capture speed at 10ms or less to avoid atmospheric blurring, is that also correct?

Thanks in advance for any input!
Hi,

Interesting question to which you will thousands of opinions and one of them is mine :mrgreen:

First of all I would say in what focal length are you thinking ? The longer the focal lens the more small scale detail you will be able to capture.

There are so many variables as Solar imagers are on this planet.

A timelapse is what the word says a timelapse. Timelapse for me is to take images at a certain time interval and then put them together and so have for example a 2 hour event reduced to 15 seconds ...

I take my Timelapses as following. Every 15 seconds I take a video of 50 frames. My camera is not the fastest as I tke at 17 frames per second. Each video I pass it through AviStack 2.0 and make a JPG image. Then I take my 200 or 300 or 400 jpg images into Adobe Premiere Elements and make a MP4 video.

I tried to find the Timelapse in CN but no success.

Maybe some other Timelapsers will chime in :?:

Below an example of one of my Timelapse videos. There are better ones in this forum then mine.

https://vimeo.com/384645495


regards Rainer

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Re: Max recommended duration of video capture to freeze small scale details?

Post by GreatAttractor »

For my captures using the 90 mm telescope (effective f = 1056 mm, image scale 0.73"/pix) I settled on 15-second videos (depending on the ROI size, 450-680 frames). For time lapses, I take 15-second videos with 30-second breaks. On the disc my setup requires 0.7-1.3 ms shutter, for fainter prominences up to 15 ms (but gain set to zero in either case).


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Re: Max recommended duration of video capture to freeze small scale details?

Post by AJamesB »

Awesome, great info everyone.

So, it sounds like the consensus for video captures meant for a still image is 13-15 seconds? And not 4 mintues, lol. Thanks! I'll experiment with this in my next session and see how my high magnification images turn out with much shorter video captures.


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Re: Max recommended duration of video capture to freeze small scale details?

Post by RodAstro »

Hi all
I just thought these two images may be relevant.
Both taken today eight minutes apart see how dramatically the two have changed especially the filament and the little dark area shaped like a horse near the spot.
Both images were taken in about three seconds.
Sorry second image is not as sharp just bad seeing and cloudy.

Cheers Rod
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Re: Max recommended duration of video capture to freeze small scale details?

Post by rsfoto »

Hi Rod,

Yes,. Quite a change. BTW I think you exaggerated a bit with the Wavelets sharpening ?


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