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Misadventures in solar astronomy (ar2822)

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#1 wxcloud

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Posted 12 May 2021 - 08:12 PM

Okay, first off, that helical focuser has gots to go. Found I need to basically be an octopus to get everything to kind of work. Seems to bind with a little bit of weight. Trying desperately to get an image, well first needed to focus and couldn't figure out why I couldn't do that. Turns out the eyepiece wasn't sitting all the way in lol.

Then I tried to tune and starting to figure that out. Once I got focus on the larger of the sunspots (now with it's children near by) I started to dial in the tuning, I'm still working in single stack mode. Once I found a decent focus I tried a few attempts to image with my phone. That didn't work. Perhaps if I had 3 hands and was sturdier. Went for the slr. Too heavy and just couldn't get focus and at one point (and yes I stuck the camera with 1.25" nosepiece into the blocking filter diagonal), I loosened the focuser on the scope enough for the camera to take a dive off to the side. Luckily I caught it. Camera went back in, decided to try the asi290mm mini, firecapture and the laptop and ran into a snag.. didn't have a long enough USB a to USB c cable.

I had already tried the afocal adapter and it didn't work. Last ditch effort for that idea I used a cheapo 10mm plossl and got things as lined up as I could. The jpg compression did a number on this. The phone complaining lens dirty, use night mode etc. But I tried. To my surprise I got a slightly out of focus sunspot and on the full image a small prominence. I also did see the smaller sunspot ar2833. Didn't photograph well...

During my fiddling visually I did see some proms (they are pretty fleeting). The tuner I managed to get a smooth solar disc to finally start looking like a textured orange.

Still trying to figure out proper imaging. Still learning to look at the sun also. Thought about a new eyepiece a bit more high powered than the 7.5mm the lunt zoom offers.

Anyway I tried to edit this photo in gimp. The dark edge is I think a tree branch lol.

Attached Thumbnails

  • bwsol2.jpg

Edited by wxcloud, 12 May 2021 - 08:13 PM.


#2 jwestervelt

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Posted 12 May 2021 - 09:46 PM

Hopefully you can get the issues worked out.

Is this a pressure-tuned scope? If so, here is a trick you can use if you are imaging with a USB camera.

 

Center the sun on the sensor.  Get the image almost focused, but not quite... a blurry limb is fine.  Set your gain to zero and your exposure so that you are around 90% at the upper end of the histogram.  Once there, start adjusting the etalon and you should see the brightness drop on the histogram.  As you continue tuning the etalon, you'll come to a point where the upper end will stop moving to the left and start climbing again.  When it is minimized, you have maximized the attenuation of the photosphere.  At that point, you can leave the etalon alone and then give attention to getting the best focus you can.  Once the focus is nailed down, you can slowly increase exposure (or gain) until the histogram upper end is around 90-95%.  That should get you pretty close to perfect for a single-stacked device.  You should find that you are able to get more detail out of your setup that way.

As for double-stacked... tune as above in single-stacked mode first, and then attach the double-stack etalon and tune until you have the most contrast with surface features such as filaments.  SharpCap and a few others have a "focusing" aid mode which uses contrast as a metric for getting focus perfect... but it also works for tuning the etalon.  Theoretically you can adjust for peak brightness when doing the double-stack, but my experience is that with the tilt-tuned devices, the "ghost" image initially lays over the top of the main image and adds to the brightness, thus making that method a bit unreliable. 

I'm sure others have their own methods, but this is what has worked for me.


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#3 jwestervelt

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Posted 12 May 2021 - 10:01 PM

During my fiddling visually I did see some proms (they are pretty fleeting). The tuner I managed to get a smooth solar disc to finally start looking like a textured orange.

Still trying to figure out proper imaging. Still learning to look at the sun also. Thought about a new eyepiece a bit more high powered than the 7.5mm the lunt zoom offers.

Proms are long-lasting... but if you aren't tuned or focused correctly, you might very well lose sight of them.  They are much easier to spot visually than with an imaging camera, at least if you want to get detail on the disc at the same time.  The eye is pretty good about adjusting to a wide dynamic range... cameras not so much.  You can certainly overexpose the hell out of the image and see very faint proms though, and that is a nice part of using a camera. 

The fact that you got the orange-peel effect is good, it means that your etalon is working and it isn't decontacted.

Solar viewing definitely is a learning curve... there are a bunch of gotchas, even after you get the etalon on-band and the image focused at the EP. 

For starters, the image might be relatively bright and you could have rather significant image retention... the remedy for this is to keep moving your gaze around.  Just like with nighttime astronomy, averted vision is your friend.  If you focus on one spot for any length of time, you'll notice the contrast fade and then you'll stop seeing detail until you glance away. 

Another thing you'll learn really fast is that magnification is not your friend.  As you increase magnification, brightness and contrast will suffer.  The temptation is always there to bump the power up, but if you are simply patient, you'll notice more in that tiny image that a 17-20mm EP provides than you will from one in the 5-9mm range.  I've seen this happen in realtime as I gave a friend a look through my scope, he seemed to be somewhat satisfied with the view, not knowing what to expect.  The next person, who had astronomy experience, was completely blown away looking at H-alpha for the first time.  He started calling out all the stuff he could see... the first person was like "what??" and when he took a second look, he started to see the fine details and learned to appreciate them.

One additional note, because of the monochromatic nature of H-alpha, you can get great views with some very low-end eyepieces.  Chromatic aberration isn't a problem, for instance, and the reduced element count often means higher transmission.  Granted, simple eyepiece designs still benefit from anti-reflective coatings, so you might want to try throwing everything at the scope and decide what works best for you.


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#4 wxcloud

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Posted 12 May 2021 - 10:52 PM

I had the rig mounted up on a star adventurer that did help this go around to at least keep the sun in the eyepiece longer while I fiddled. Unfortunately the rig was pretty unstable, well, the tripod was, was fairly easy to twist things and move the image. Might need to get the AVX mount in rotation. Was trying to track and keep things pretty simple but focus and tuning shook the image pretty bad.

The scope is pressure tuned, it's the LUNT LS50THA. I think I lost the fleeting proms whilst fiddling with trying to get images, knocking the focus and tuning out of whack.

Perhaps I'll try a couple other wider eye pieces, got the 13mm nagler and 24mm pan. Another issue I've noticed is me... Just trying everything at once or I'll see something I like and then see what else or how I can get better views and end up knocking a good view out of whack instead of slowing down. Yeah, I'm a little overenthusiastic at times :) and I'm still learning this particular scope. I think I'm eager to image so I can go back later and see what all I might have missed or help me recall and confirm what I seen.

This is actually getting pretty interesting :)

#5 jwestervelt

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Posted 12 May 2021 - 11:20 PM

Don't rush things... be patient.  That goes for all things in life.




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