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Stack or Static for Solar Eclipse?

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#1 anjin_nav

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Posted 04 February 2024 - 04:55 PM

I'm planning on photographing the 2024 eclipse with my new ASI2600MC Duo. There is a large range of exposure time, depending on whether you want to feature the Bailey's Beads, solar prominences, or corona. My question: is it possible to simply stack a bunch of shorter exposures?



#2 auroraTDunn

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Posted 04 February 2024 - 05:58 PM

I HIGHLY recommend you pre-plan what you want for final images and then plan out completely what you need to get that/those images done.  Then set everything up for that shot sequence and practice taking your images, even if your not aiming at the sun, but do take into account that unless you are using a tracking mount that you will have to adjust your aiming. I suggest you get some sort of remote for taking you images as well. You do not get long and if its your first you will be totally taken back by the event and you want to take it ALL in, the spectacle, the people around you, the change in the temperature, just how quick it becomes dark, as in pretty dang dark. It's something you will never forget so make sure you get your images but enjoy the whole thing.

 

As for your actual question. I suggest think towards stacking, but not JUST stacking but stacking via HDR processing. With that approach you will be able to recreate pretty much anything you desire. I often take an entire month plus carefully processing my images afterwards and LOVE every second of it.

I'd love to show you some of my images, at least my most fav image from the 2017 eclipse but alas my brand new workstation suffered what I believe is a melted power cable for my 4090RTX card (and trust me my vendor I had build this machine is not going to enjoy my call tomorrow! I can't even switch between my memory tower without first logging into that workstation to open the network.


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#3 auroraTDunn

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Posted 04 February 2024 - 06:16 PM

Actually I kind do have access, via my Meural Digital frame,

Eclipse-2017

 


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#4 whwang

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Posted 04 February 2024 - 07:47 PM

I suppose you are asking if you can take a bunch of 0.1 sec exposures throughout the totality, instead of 0.1, 0.2, 0.4, 0.8, 1.5, and 3 sec exposures.

 

If that's your true question, then the answer is it's theoretically doable, but practically challenging.  All you get is you don't need to worry about changing exposure time.  But there are two major drawbacks:

 

1. During the few minutes of totality, the sun, moon, corona streamlines all move relative to the background stars.  Your mount can have tracking errors from a couple of arcsec to as bad as more than 10 arcsec (unless you have prefect polar alignment plus pointing models using a mount with high-resolution encoders).  All these motion will blur your stacks. Since your exposures are short to start with, it's very likely that the S/N is not high enough in each exposure for you to register the relative motion using background stars or using the corona streamlines.  All you can use for registration is the lunar edge, but the moon moves.  

 

2. You will need LOTS of exposures.  Using the above 0.1 to 3 sec sequence as an example.  The 0.1-sec exposure is likely to be dominated by camera's readout noise.  In readout noise limited regime, if you want to have a result equivalent to a 3-sec exposure, you will need 900 0.1-sec exposures.  Is your camera fast enough to take 900 exposures in a couple of minute?  Even if it can, with all these effort (including overcoming the image registration challenge), is it really worthwhile just to get a result that's equivalent to a single 3-sec exposure?

 

If you are using the latest bunch of mirrorless cameras, I would actually encourage you to go this route, since they are all incredibly fast.  Instead of taking 900 0.1-sec exposures, you can take tens of 1-sec exposures and skip the 3-sec ones.  (You will still need different exposure times for shorter ones.).  I believe many mirrorless users will start to take this approach, including myself.  But since you mentioned an ASI camera, I would say forget about it.  The readout overhead is just too large.


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#5 t-ara-fan

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Posted 04 February 2024 - 07:48 PM

Stack?

Before totality: no time, not much point. The image is very bright and low noise. And the sun changes every second, so you can't stack different images.

During totality: take a half dozen different exposures so you can make a HDR shot of the corona.

Edited by t-ara-fan, 04 February 2024 - 07:48 PM.

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#6 anjin_nav

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Posted 05 February 2024 - 08:19 AM

Hi, All.

 

Thanks for the tips. I was at the 2017 eclipse, and I have a decent enough shot using HDR. At the time I used my DSLR with a remote and a rented 600mm lens. This time I hope to have it set up on my old mount and 430mm telescope. Not so concerned about that rig--other than it's a full-frame camera on a shorter FL, so I won't have as much zoom. The other rig is my brand-new mount (with RA encoder), ASI2600MC camera, and Askar 130PHQ with the 0.7 reducer.

 

I want my fiddling time to be minimal, so I wanted one rig to run as automated as possible. Honestly, my main concern right now is the ASIAir. I know I can set up a plan to run, say 10 shots at 0.1 sec, then 10 shots at 0.5 sec, followed by 10 shots at 1 second, then in reverse. I need to experiment with how many shots I can cram into 4 min 27 second, since I know the ASI needs some time to clear the buffer.

 

The other option seemed to me to take a video of the whole sequence and stack the frames like you would in planetary imaging. I just wasn't sure if it had been tried or is even theoretically possible.



#7 anjin_nav

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Posted 05 February 2024 - 08:20 AM

I HIGHLY recommend you pre-plan what you want for final images and then plan out completely what you need to get that/those images done.  Then set everything up for that shot sequence and practice taking your images, even if your not aiming at the sun, but do take into account that unless you are using a tracking mount that you will have to adjust your aiming. I suggest you get some sort of remote for taking you images as well. You do not get long and if its your first you will be totally taken back by the event and you want to take it ALL in, the spectacle, the people around you, the change in the temperature, just how quick it becomes dark, as in pretty dang dark. It's something you will never forget so make sure you get your images but enjoy the whole thing.

 

As for your actual question. I suggest think towards stacking, but not JUST stacking but stacking via HDR processing. With that approach you will be able to recreate pretty much anything you desire. I often take an entire month plus carefully processing my images afterwards and LOVE every second of it.

I'd love to show you some of my images, at least my most fav image from the 2017 eclipse but alas my brand new workstation suffered what I believe is a melted power cable for my 4090RTX card (and trust me my vendor I had build this machine is not going to enjoy my call tomorrow! I can't even switch between my memory tower without first logging into that workstation to open the network.

Sorry to hear about your workstation. I hope you can recover it soon.



#8 t-ara-fan

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Posted 05 February 2024 - 01:01 PM

  Not so concerned about that rig--other than it's a full-frame camera on a shorter FL, so I won't have as much zoom. The other rig is my brand-new mount (with RA encoder), ASI2600MC camera, and Askar 130PHQ with the 0.7 reducer.

 

  I know I can set up a plan to run, say 10 shots at 0.1 sec, then 10 shots at 0.5 sec, followed by 10 shots at 1 second, then in reverse. I

In 2017 I just barely got the corona in the FOV with a Canon 7D Mk II (APS-C), Canon 200mm lens, 1.4x extender.  So 280mm on APS-C equivalent to 420mm on FF.    So I wouldn't worry about that 430mm with FF scope not zooming in enough. 

 

This pic is slightly overexposed but it shows the extent of the corona. And no, I didn't have time to even think about rotating the camera while enjoying the eclipse.

 

0B9A6330_2000x1333.JPG
 

With your 130mm scope you will be zoomed in for sunspots, prominences, and the diamond ring.  But the corona will definitely be cropped.  Is it worth complicating the event to run two systems? 

 

Do we expect the corona to be bigger this year due to more solar activity?

 

Your choices of 0.1, 0.5, and 1.0 second would be better distributed from a HDR perspective at 0.1, 0.3, 1.0 seconds.

 

Maybe expand that range and don't take 10 shots at each exposure? 

 

With my rig described above, I shot the corona in totality at ISO100,  with exposures ranging from 1/125sec @ f/8 to 1/4 sec @ f/5.6.   The one second exposures were completely blown out.  You might consider 0.01 seconds at low gain as a start point.  In fact, since eclipses are rare, why not start at 0.001sec?  


Edited by t-ara-fan, 05 February 2024 - 01:09 PM.

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#9 auroraTDunn

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Posted 05 February 2024 - 03:08 PM

Thats an excellent point. I used my 100-400 close to the 100 to get the corona in.

And yes this year I would expect a larger/active corona and probably more/better prom's.

Stil trying to decide what I'm taking with me this year. Half tempted to take my RedCat 71 with one of my other cameras plus my canon again.

 

Honestly though, one of THE best parts of eclipses is all the people around you. Best parties ever!!!


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#10 Domer

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Posted 05 February 2024 - 03:37 PM

I couldn't decide whether ot use a DSLR (Canon 6D Mark II) or my ASI2600MC, so I'm using both (see photo below).  The challenge I'm facing now is determining the appropriate exposure times for the ASI2600MC.  There is a ton of information online for how to configure your DSLR for proper exposures during all phases of the eclipse, and I have Eclipse Orchestrator Pro programmed to control every aspect of the DSLR sequencing.  But there is precious little information describing how to determine the exposures times for a dedicated astrocam.

 

I did some experiments yesterday to determine the relative exposure ratio between the two optical trains by attaching a white cloth to the telescope and camera lens, then pointing the rig to a clear spot in the sky about 10 degrees from the sun (so bright, white light).  Then I took exposures with each camera until I got similar histograms and peaks.  I double-checked that the magnitude of the pixels in the center of each image were also similar, since vignetting will skew statistical results.  I was suprised that the ASI2600MC exposure was 1/10th of the DSLR.  The difference in f-ratio for the two optical trains only accounts for 3x (f/6.3 for the DSLR, f/3.58 for the ASI2600MC).  The QE for the ASI2600MC is > 80% while the QE of the Canon 6D Mark II is 52%, so the ASI2600MC will capture ~60% more photons per unit time, but those two differences combined only explain about half of the 10x ratio.

 

I'm going to run more tests when the weather clears.  But if all the results are consistent, then my ASI2600MC exposures will all be much shorter than the DSLR.

 

Another thing I learned is that I can download images from the ASI2600MC MUCH faster if I disable debayering in NINA, which is what I'm using to control that optical train (using Eclipse Orchestrator for the DSLR).  NINA won't issue a new exposure command to the camera until debayering is complete and that takes a while on a laptop.  I'm not sure how ASIAir, ASICAP, SharpCap, or other software programs work in this regard, but it was a significant finding for me as it allows me to take many more exposures during each phase so I can broaden the exposure brackets to ensure I capture the right exposures.

 

 

Eclipse Rig Details.jpg


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