Monday, May 8, 2017

Astro Imaging and Processing the Sun

This tutorial is taken from SkyatNight Magazine and written by Pete Lawrence.
I think this tutorial can be very helpful for our members that enjoy the Sun as much as the stars. 


Before pointing your setup at the Sun, check and fit your white light filter and remove or cap any finderscopes. Locate the Sun using your camera and focus on a sunspot or the limb (I recommend getting and using a dedicated solar finder or you can use scope's shadow... much easier ~ km). Center on the middle of the solar disk and check for overexposure – there should be no white visible. The levels meter should read just less than maximum.


Move the telescope (slightly) in RA. Orientate the camera so that features on the Sun move parallel to the bottom of the image frame. Push the front of the scope up, note the direction – the leading edge of the sun is the northern limb. Apply pressure to the front of the scope to push it to the West; the leading edge of the sun is the western limb.


if your software allows, reduce the gamma on the image to make the Sun's surface easier to see. A green or solar continuum filter over a monochrome camera can enhance solar granulation. Record 500 – 800 frames or each section of the Sun: make sure that captures overlap. Process each using a registration and stacking program.


Load the first processed frame into a layer–based graphics editor and cropped off any white borders. Increase the canvas size with a black background to accommodate the final image size. Open and adjoining frame and draw a selection box around the image that cuts off the border. Paste this into the base frame as a new layer.


Align the upper layer using surface detail. If there are no sunspots, try using solar granulation –  it's tricky, but possible! Move the upper layer roughly into position then toggle its visibility on and off to align. Once done, use the Curves tool to match tones approximately. Remove any share overlaps using an Eraser tool set to 10%.

Repeat for all mosaic frames then flatten the image. Taking a sequence of white light mosaics over several days allows you to reveal the Sun's motion: load each mosaic into your graphics editor, in order, as separate layers. Align them and set the blend mode of all upper layers to darken to show the spots on the layers below.

This all sounds good to me and should be easy to do in Photoshop, however I have not tried to use this tutorial. Above all be very careful imaging the Sun.