H-alpha SHG at 910mm focal length

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thesmiths
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H-alpha SHG at 910mm focal length

Post by thesmiths »

Our most recent SHG experiment is to combine a Sky-Watcher Evostar 90 refractor (90mm aperture, 910mm focal length) with our 2400 l/mm SolEx-style SHG. The telescope was the same one we used for some earlier experiments with a PST mod viewtopic.php?f=9&t=32108. It has a sub-aperture 25A Hoya 82mm red photographic filter inside to reduce the light intensity. Here is a photo of the setup, which looks somewhat similar to a PST mod. It is mounted on a Vixen GP2 and the whole telescope plus SHG is quite light, only 3.5 kg.
910mm FL, 90mm aperture, 2400 l/mm SHG
910mm FL, 90mm aperture, 2400 l/mm SHG
1260.jpg (192.92 KiB) Viewed 741 times
The collimator is a 100m Pentax macro bellow lens and the camera lens is a generic 100mm M42 telephoto. The camera used was a ASI 290MM with a 1.5x magnifier. The diffraction grating was a 30mm x 30mm, 2400 l/mm holographic from Edmund Optics. The initial testing went surprisingly well. The imaging was done late in the day, with some intermittent clouds, through an open bedroom window. So definitely not idea conditions. The 20 micron wide slit (from Thorlabs) is 3mm long so a single scan covers about 1/3 of the solar surface. Here are images of the top and bottom of the disk:
H-alpha, 7 Nov 2021
H-alpha, 7 Nov 2021
135507_clahe.jpg (258.85 KiB) Viewed 741 times
H-alpha, 7 Nov 2021
H-alpha, 7 Nov 2021
135550_clahe.jpg (245.23 KiB) Viewed 741 times
The gain of the ASI 290MM was set to zero, the exposure was 1.65ms and the fps was 418. Some interesting prominence structures were visible from the same data:
H-alpha prominences
H-alpha prominences
135559_protus.jpg (116.89 KiB) Viewed 741 times
H-alpha prominences
H-alpha prominences
135640_protus.jpg (60.77 KiB) Viewed 741 times
Finally, here is a pixel-shifted mosaic of the data from above. The top left is unshifted and the bottom right is shifted by 22 pixels (2 pixel increments in between). Far from the centre of the H-alpha line, the image looks essentially like a white light image (a sunspot is visible).
H-alpha pixel shift 0 to +22
H-alpha pixel shift 0 to +22
135550_shift=0-22.jpg (298.58 KiB) Viewed 741 times
See this post by Pedro for images taken on the same day as these viewtopic.php?f=4&t=33914
Last edited by thesmiths on Mon Nov 08, 2021 1:48 pm, edited 1 time in total.


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Re: H-alpha SHG at 910mm focal length

Post by marktownley »

Very impressive results Douglas!


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Re: H-alpha SHG at 910mm focal length

Post by Montana »

Wow!! these really are amazing, well done :bow :bow :bow

Alexandra


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Re: H-alpha SHG at 910mm focal length

Post by thesmiths »

Thanks. The jadedness at the solar edge is, I assume, an indication of the poor atmospheric conditions. Given the relatively slow data acquisition process, I think the SHG method really benefits from good seeing.

By the way, the upgrade to my Vixen GP2 mount with Astro-Gadget EQStarProEQ5 stepper motors has been very successful. I think the belt drive system gives more uniform scanning (less backlash, etc). Also, the interface to EQMOD is helpful since since previously I need to use the hand controller for scanning. I can highly recommend this upgrade for older mounts of this sort.


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