Seeking help with PST imaging and Double Stack

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fjwallace
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Seeking help with PST imaging and Double Stack

Post by fjwallace »

Hi,
I am new to this group but have been using and photographing with my PST for many years. I am a retired educator and had used this scope in my classes and went to other schools to show the Sun and continue (when there is no CoVid) to go to schools and other venues for free as a NASA Solar System Ambassador. I take images every clear day I can and share them with teachers and others. That said, I never had anyone that explained how to use it ‘properly’ and thus I have a series of questions that follow (I apologize for the length of this note but I’ve been looking for help for a long time):
1) I recently sent my PST to Meade to be cleaned and ‘tuned up’ and after 14 weeks (they lost it for a while), I got it back. I found it was much easier to focus and all but it had a smudge on the bottom corner of the filter that is in the eyepiece cup. It isn’t a big deal for visual but makes things a bit more difficult for photography. Can I clean this with lens cleaner supplies? I don’t want to mess up the filter coatings but I don’t want to send it back to Meade!
2) I’ve noticed that my PST has a very narrow ‘sweet spot’ – where the entire disk of the Sun is fairly close to the same brightness (no super bright areas or really dark areas!). This is what I use for taking images but it isn’t where features are at their best! When I tune the telescope, it seems to work in ‘bands’ across the Sun rather than the entire disk going into and out of ‘tune’. Is this just something we need to live with or am I doing something wrong?
3) I have read about taking 'flats' with other scopes (Lunt and Daystar) and tried their method of using a cereal box liner/ wax paper. This did not work for me. I hoped someone using a PST might have a way to take a flat that would work for the PST. I currently use Firecapture and AutoStakkert which came with the camera.
4) I have owned a double stack filter for many years as well but each time I use it, it doesn’t seem to improve the image quality or resolution. I finally contacted Meade/Coronado to get their directions and I followed those and took some images with my ZWO-174MM camera. Here’s what they say: 1) Focus for sharp disk (crisp edges); 2) Use the T-Max thumbwheel to either remove or minimize any ghost image; 3) Use the RichView tuner to tune in on the surface or limb detail as desired... I am going to try to include some images to show my observations. I think the processed images (both done the same in PS cc 2020) show the single stack images are much better (I took two of each in case there was some haze or wind and chose the best images). I also found the prominences were much worse with the double stack – very ‘fuzzy’. I assume I am doing something wrong and hope someone can help me out.
I am including some images and include a final composite image I created on that day - all converted to JPG to reduce size.
Initial surface image
Initial surface image
01 031621 sur np.jpg (163.97 KiB) Viewed 710 times
Initial surface image double stack
Initial surface image double stack
01 ds 031621 sur np.jpg (156.29 KiB) Viewed 710 times
Processed surface image
Processed surface image
02 031621 sur p.jpg (279.99 KiB) Viewed 710 times
Processed surface image double stack
Processed surface image double stack
02 ds 031621 ds sur p.jpg (284.63 KiB) Viewed 710 times
2x Barlow ss
2x Barlow ss
03 031621 Barlow ss.jpg (248.35 KiB) Viewed 710 times
2x Barlow ss double stacked
2x Barlow ss double stacked
03 ds 031621 Barlow ss.jpg (271 KiB) Viewed 710 times
Final Composite Image
Final Composite Image
04 031621 comp color dot s.jpg (437.68 KiB) Viewed 710 times
Thanks for any help you can provide!
Jon


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Montana
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Re: Seeking help with PST imaging and Double Stack

Post by Montana »

A very warm and sunny welcome Jon. That doesn't look too bad at all Jon. The single stack looks to be working well but you do have the sweet spot a bit off centre. When you image you need to get the Sun in the bottom right corner to get a more even illumination. You can crop in Photoshop later to get it centred. I have to do this for my PST.
Using a very large pixel camera won't help you get much resolution with a PST, you need to pick a camera with a small pixel size, I recently purchased a FLIR Chameleon with a 3 micron pixel size and it works great apart from the Newton's rings :( I find the double stack dims everything but the prominences stand out more. Here is a link to a recent shot with my double stack PST https://www.flickr.com/photos/alexandra4/50978776213/ I have to do 2 shots and zip them together so sometimes they don't merge well either, depends on the day.

Get the single stack tuned well first. Then add the double stack, start with the wheel turned all the way in first then gradually turn it till the ghost disappears and maximum contrast is displayed. Once I found this place, I then rotated the etalon (unscrewed it) around 180 degrees and found I had much better uniformity (called clocking). However, be very careful, don't unscrew it all the way off so it falls off, you just need to investigate 270 degrees of turn. Try 90 degrees, 180 and 270.

I hope this helps a bit.
Alexandra


fjwallace
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Re: Seeking help with PST imaging and Double Stack

Post by fjwallace »

Montana,
Sorry for the slow response! Thanks for your comments. I'm afraid the bottom right is where the smudge is and I need to clean it and was wondering how to do that since it is a coated filter. I use the ZWO 174mm which was recommended for solar but I agree, the pixel size seems too large and may look into getting a different camera. I think my problem must be that I am not getting a good tune in single stack to begin with and can't then double stack and tune.
Thanks again!
Jon


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