Some Thoughts on SharpCap and the April 8th Solar Eclipse

[russw]

Last night at CRO, Andy and I spent some time talking about imaging the upcoming April 8th solar eclipse. I spent most of the time extolling the virtues of SharpCap, the app that I will be running on my Windows laptop to control my ZWO camera and Celestron CGEM mount. One SharpCap feature we discussed in particular is a relatively new tool called “feature tracking.”

Feature tracking lets SharpCap use your connected ASCOM mount to guide the telescope and track on-screen image features like the solar disk. It works much like PHD2, which guides on stars, but instead uses the center of mass of a disk-shaped object like the Sun, Moon, or planet to guide the mount to keep the object centered. This guiding can be done using the imaging camera and scope, or using a separate finder scope and camera.

The developer states that this feature is not intended to provide “pixel perfect” guiding, but instead is just intended to keep the target object from drifting to the edges of the field of view. I’ve been testing feature tracking on the Sun, and in my estimation, it works very well in preventing significant drift and does much better than just keeping the Sun within the field of view.

Feature tracking is only available in SharpCap Pro (~ $15.00 per year), not the basic free version.

The screenshot below shows the feature tracking window while I was imaging and guiding on the Sun recently on a very windy day. Despite showing quite a bit of movement (caused by the wind), SharpCap kept the Sun well-centered in the field of view with very little drift throughout the session.

Andy also mentioned, and I wholeheartedly agree, that during the eclipse, your mount should be set on the solar tracking rate, not the usual sidereal rate for tracking stars. SharpCap allows you to select this tracking rate as shown in the screenshot below (along with some other useful items).

One brand new feature of SharpCap that might be of interest, and possible use, during the eclipse is its lunar, solar, and planetary live stacking mode. In this mode, you can capture, live stack, and apply wavelet sharpening and other enhancements in real time right at the scope. And, the resulting images can be saved manually individually, or automatically in a time lapse mode. The screenshot below shows a recent 50-frame live stack of the Sun with a very small touch of wavelet sharpening.

Finally, just one last comment. I’ve seen a lot of solar images lately where the Sun’s central region is blown out bright. I’ve found that with my rig, manipulating the exposure, gain, blue and red balance to keep the max luminance (white) histogram at or below 60%, and max color (e.g., red) histogram at or below 80% prevents this. The screenshot below shows the histogram shape that I will be dialing in for the partial phases of the eclipse to get a pleasing color balance that is not blown out bright toward the interior of the solar disk.

[Andy_Fryhover]

Super good talk last night Russ. I bought the yearly license and will start using SharpCap more often. I’ll be testing in the backyard every chance I get before the eclipse guiding on the sun. I don’t care how good your polar alignment is, I’ve always seen the Sun drift a bit over the time of 3-4 hours. The less drifting = the better your stacks and images will be.
I’ll probably add a small guide scope to keep locked onto the sun. Thanks again for all the info.

I really think everyone who doesn’t use the ASI Air platform to revisit SharpCap with all its upgrades.

Dang, I just thought of something. I wonder if I use my off-axis guider and sun guide with surface features or part disk??? That you eliminate one more scope! I might try this.

[russw]

Andy,

That’s a really good idea about using the OAG. I’d be very interested to hear the results of your backyard testing.

Also, i don’t know this for sure, but as you suggest, guiding on a surface feature (e.g., sunspot) might give even more precise guiding than center of mass of of the solar disk. I haven’t gotten that far yet with my trials of feature tracking.

[gr82bgd]

Very interesting discussion. Too bad that I wasn’t at CRO to join in. I have never used sharp cap, it is on my to do list. I have the free version downloaded but just haven’t taken the time to try it out. I have so much time and effort in Astro Photography Tool.
Back to the topic, it my understanding the during Totality the brightness changes so drastically that the astronomical cameras may not be able to transition fast enough to capture the details, I pretty sure both of you are much more knowledgeable than I am on the subject. I watched a presentation by Alan Dyer and he doesn’t recommend using an astronomical cameras. I know he is DSLR photographer and may be bias on the subject. But I will kept watching this discussion with interest to see if I will bring along my astronomical setup?

Thanks…
Stan

[russw]

Stan,

I’m not sure what it means that an astronomical camera (non-DSLR?) cannot transition fast enough to capture details during totality. At the 2017 total eclipse, I used a cheap planetary camera (ZWO ASI120MC) and a cheap Orion refractor to capture the diamond ring effect, the inner corona, and a string of pink prominences along the solar limb. It wasn’t that difficult.

Of course, I was just running a single rig, not multiple DSLRs at multiple focal lengths, on separate mounts. Running a multi-rig imaging operation is not how I want to experience totality.

I hope to take some time from my imaging rig (as I did during the 2017 eclipse) to marvel at the darkness, the stars and planets in the daytime sky, the magnificence of the corona, the street lights coming on, and the exclamations of wonder of the people around me.

But, you raise a good point about the time investment necessary to learn a new image capture tool. SharpCap would have a learning curve. And, it does not work with DSLRs. If you are comfortable and familiar with Astro Photography Tool and Eclipse Orchestrator, you should probably stick with them.

I’m coming at it from a non-DSLR perspective. For someone who is going to use a non-DSLR camera as their imaging device, I think SharpCap is the way to go. SharpCap could also be useful for a DSLR operator who needs to guide their rig during the partial phases of the eclipse.

Finally, for the 2017 eclipse, I used FireCapture for image capture. Although FireCapture is a planetary imaging app, it is still a good program for this type of imaging with a non-DSLR camera. But, I think the recent major upgrades to SharpCap (mentioned above) make it the better choice this time around.

[Andy_Fryhover]

Using an OSC astro cam should be fine if you have some kind of exposure assistance or can make quick changes and if you know your setup well. They are also good because they will pick up Ha and reds that ring the surface. I want to maybe use my cooled APS-C ASI2600mc for a video of the eclipse. I’m doing all kinds of experiments. The off-axis guiding did not work today. The pick-off mirror prism just caused way too much glare, I couldn’t get any surface features to lock on to and guide from. So now, I’ll try a separate guide cam and scope.

Cool thing, my solar filters for my binos fit my 60mm guide scope

[gr82bgd]

Russ,
I like said you know about this than me. Sounds like you have already been able to get the astronomical cameras to work just fine. I knew you probably had everything figured out. I wish you much success. I may have to look over your information more closely and possible give it a try.
I am kind of in the same boat as you. I used the DSLR in 2017 and feel comfortable using it. In 2022 I got my first astronomical camera and I really like it, but I still have lots to learn.
That’s what makes these discussion so valuable, there is always something to learn for those with more experience.
Thanks…
Stan

[gr82bgd]

Andy,
Your images of the sun with your mono camera and Ha filter are very interesting. After reading your and Russ discussion I need to get my ASI2600 mc and give it a try. I just never would have thought it could image the sun? I appreciate you both sharing this and give me some ideas to try out.

Thanks…
Stan

[russw]

Stan,

I think comfort and familiarity with the equipment we have is the important thing at this point. We only get one chance to get it right. Next total solar eclipses to touch the continental U.S. are not until 2044 and 2045. Looking on the bright side though, this gives us plenty of time to practice and get ready.

[russw]

Andy,

What good luck that the solar filter for your binos fits your finder/guidescope.

I am disappointed that the off-axis guiding didn’t work out. I thought it was a really good idea. I’m hopeful, however, that the finder/guidescope method will. It looks like you are all set up to give it a go.

BTW, what camera is that hooked up to your finder/guidescope? A ZWO for sure, but I can’t tell which one.

[Andy_Fryhover]

That one is a 178mm, but I also have a 174mm and a 120mm. What do you think about a 2x barlow on my 60mm F4 240mm focal length guide scope? I just got home from work and I’m tired so testing setups will have to wait another day.

[russw]

Andy,

My educated guess about whether to use a 2x Barlow is that it depends on how you will expect to guide. If you want to guide on features (e.g., sunspot), the 2x Barlow would be the way to go. But, you are taking a gamble that there will be a large enough sunspot group in view on the day of the eclipse.

Center of mass guiding should work with or without the 2x Barlow. But, I don’t know how well center of mass guiding will work as more and more of the Sun disappears between the start of the eclipse and totality.

Also, using the 2x Barlow might affect your ability to achieve focus. Unfortunately, probaly necessary to test.

If it’s any help, here are the numbers and FOV simulation for your 60 mm f/4 & ASI178 with and without the 2x Barlow.

Images created with: 12-D String FOV Calculator/FOV Simulator
http://www.12dstring.me.uk/fovcalc.php

[Andy_Fryhover]

Yes, I agree with everything you are saying. After this weekend, I’ll be taking apart all my “deep sky” imaging equipment and then focusing only on solar build-out and testing every day until the eclipse. I was playing around with the field of view for my three guide cameras in Stellarium. That will be interesting to see how guiding will be affected as the sun changes shape and brightness etc. I still plan to have the guidescope on the rig and try to guide with SharpCap to help reduce even the slightest amount of drift. My zoomed-in view at 1500mm and full frame cam, I don’t want and drift going on.

[russw]

Andy,

That sounds like a plan. After this weekend, I too will be tearing down my semi-permanent backyard set-up and getting everything configured and packed for the eclipse.

[jt_3232]

Thanks for the tip on Sharpcap and the feature tracking! I used that today, although when the disc got small during max totality, it didnt really work and i had to manually track. It was nice otherwise!

[russw]

Hi Jaxon,

I’m glad it worked for you.

We deployed by car to Oden, Arkansas from our RV campsite in Broken Bow when it looked like Broken Bow would be clouded out (turns out it wasn’t). The older lighter weight mount I had in the car for a re-deployment contingency hadn’t been tested under SharpCap control so I just guided manually using the handcontroller like I did for the 2017 eclipse. Wasn’t much of a problem though. Just needed some minor corrections every five minutes or so. Must have accidentally gotten polar alignment pretty close using compass and clinometer.