Solar images of 2 halves and resolution tests.

Last Friday was brilliantly clear all day – until it got dark! So, I managed to get some tests done from the window-sill solar observatory without being in any particular hurry. I have already posted some images from the day.

The Mikrokular full HD camera, is just that – full HD, 1920 X 1080, and that primarily, is why I bought it. The question is how to make best use of it. The focal length of the Lunt LS35THa and the chip size is such that I can’t get the whole solar disc in one frame, and getting the whole disc with a reasonable number of pixels was one of my other objectives. So we are left with taking 2 images and stitching them together. I made a X1.5 barlow (reported elsewhere) in order to maximize utilisation of the available pixels, but I have had variable results with Canon’s Photo-stitch and Microsoft’s Image Composite Editor. The problem is that the solar scope produces a variable contrast image across its field. This is of little consequence visually, and if you are only imaging one frame. However, when you try to stitch images together you get an unsightly ”seam” between the 2 images. After a lot of head scratching and many trials, the best I have achieved is to create 2 “layers” for the 2 images in GIMP, align them manually and then merge them using a graded layer mask across the region where they overlap. (If this sounds like gobbledygook, it will become clear if, and when you do some image processing! Don’t forget GIMP is FREE legitimately!). The bigger the overlap, the better this works. So, here is an image with no barlow and lots of overlap, and another with the X 1.5 barlow with more pixels and not much overlap. This one also had more processing than the no-barlow one.

Solar disc - no barlow
Solar disc – no barlow
Solar disc with X1.5 barlow
Solar disc with X1.5 barlow

I also did some detailed images with a X2 barlow and the 2 barlows cascaded together to make X3 to see if the extra resolution you get like this significantly improved the images. I’ve extracted the spot and the prominence from the full disc images to compare with the ones with the more magnified barlow images. The spot is the best indicator, as it seems if the prominence was changing over the duration of the test. I have also re-sized these images so they are all the same number of pixels so that the intrinsic resolution can be compared better.

Resolution tests
Resolution tests

Well, it is not super-rigorous, but interesting, nevertheless.

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