21st Feb Ha Sun

[Maurice]

Hi


Attached is a Ha image of the sun taken on the morning of 21st Feb in fair seeing with my home made SHG + 100mm ED refractor at f/9.


Best 8 of 12 reconstructed scans selected and stacked in AsustoStakkert3! and sharpened in Astrosurface.


Reduced image attached here.
Better one that can be downloaded here:


https://flic.kr/p/2qMVAXm


cheers
Maurice

[Saturn488]

Very nice image!

Do you have photos of the SHG and some documentation regarding it?

[Peter Ward]

Yet another top-shelf result. :thumbsup:

Sadly not much blue sky north of the border. :rain:

At least the garden is enjoying it :)

[Maurice]

Hi

Glad you like the image.

Photos attached here show a completed setup annotated image, as well as some construction images along the way.

My original design used a 150mm fl /135mm fl lens combination as imaging lens/collimating lens, but I then changed this to a 200mm fl collimator with a 150mm fl imaging lens.
Basically, the easiest way to increase spectral resolution of the system was to increase the FL of the collimator.
My original calculations are shown in the photo of "calcs by hand". Then I found Ken Harrison's great spreadsheet "SimSpec" which does it all for you. It makes trying out different options a breeze. See the PDF attached for a screenshot of the spreadsheet output.

The "grating holder and rotator" image shows my original grating collimate-able cell which I attached to an old 6:1 reduction from a focuser to allow for more precise wavelength selection when rotating the grating. I have since motorized all of this with a mini controller and old LCD screen - see the "Auto grating rotator" photo.
I can set pre-defined wavelengths to slew the grating to, and have easy control of it by either pushbutton movement or rotary encoder movement.

The "slit holder" image shows a 9 micron wide x 12mm long slit in an 1-1/4" filter cell. The length of this slit allows for a main telescope FL of 1000 to 1100mm or so. I am currently using a 7micron wide slit for even higher resolution spectral sampling. The "slit holder sun facing side" shows how the slit can be rotated for collimating purposes. Note the narrow slot that only allows for a small amount of solar energy to hit the slit at any time.

Other images show the setup viewed from the LH and RHS. Note that I have made an ASCOM focuser for the imaging lens which makes focusing the spectrum easier.
The main scope has a basic electric focuser for focusing the sun's image onto the slit. I have left the collimator focusing to be manual ATM, but will look at changing this in the new SHG that I am designing.

Note that unlike conventional SHG attachment, I use 2 diagonals to reflect the spectrum up and back on top of the main scope. This makes for a more compact and mechanically stiffer arrangement.

Specifications for the current setup are as per the attached PDF spreadsheet.
100mm f/9 main scope
7micron x 12mm long slit
2400l/mm 50mm x 50mm diffraction grating
200mm fl collimator
150mm fl imaging lens
ASI183MM camera
Spectral sampling at Ha approx. 0.05A/pixel

In the annotated image I also show a solar scintillation monitor that I made in order to gauge the quality of the local seeing.
This has an OLED display which graphs the seeing conditions in real time, but can also send the data to my PC for graphical output in "Firecapture" planetary software.

Sorry about the rant - but you did ask... :)

Cheers
Maurice

PS looks like I have reached the image upload limit for this message...
A few items have dropped off my attachments list...






Thanks Peter.
Too hot and very windy here today.
Not good for solar imaging....


cheers
Maurice

[Maurice]

Trying to attach the other bits here....

[Peter Ward]

I am always in awe of amateur astronomers who make custom instrumentation that exceeds the performance of commercially available gear.

Wonderful stuff! :bowdown: