Solar photography

[Tony Laverick]

I am about to take delivery of a Seymour Solar SF950 glass solar filter to fit my Celestron Nexstar 8SE. I have a ZWO ASI 462MC colour imaging camera and would like to take photographs of sunspots.

I am a complete novice and have only relatively recently acquired this kit. I have never attempted solar photography before and I should be grateful, therefore, for some advice on how to achieve the best results. I have no idea, for example, of exposure times. I have downloaded SharpCap 4.0 and AutoStakkert for image capture and processing. Any tips on what settings I should use will be gratefully received.

Many thanks in advance,
Tony Laverick

[Daryl Dobbs]

I just binned one of these, I’ve had it for 5-6 years but rarely use it preferring a Herschel wedge, but hold it up to the light and check for pinholes. I stored mine indoors in a clean plastic bag in a foam case, when I had it new I noticed a cluster of  pinholes but a couple of weekends ago I got it out and the result is the picture below. According to Seymour the coating is on the back,  (I thought it was sandwiched between layers of glass) and they recommended using a black permanent marker pen to cover them, something the good people on the Solar Chat forum which the BAA is a sponsor recommended not to do as it could endanger your eyesight and the camera chip. Since I haven’t used it for quite sometime and it’s remained in its case indoors, I’ve no idea how the pin holes became so large, perhaps flaking over time around the edges? as they were nowhere near as large as this the last time I used it. The filter in the picture below fits a 90mm refractor, I drilled a very small hole in the dew cap which the screw passed through as it nearly blew off in a gust of wind.

I did ask Seymour if the coating degrades over time or if it was flaking around the edges caused by incorrect storage, ( can’t see how I could have stored it any better) but they only suggested the black marker pen. Out of curiosity when they told me the coating is on the back I tried to scratch it with my fingernail, but couldn’t make any impression on it.  

[David Arditti]

You should get very good results from your setup Tony. Have a look at FireCapture (which is free) for video capture with the ASI764MC. I don’t know how it compares with SharpCap for this purpose, but I use FireCapture. The exposure required is likely to be in the 0.001s range, but in FireCapture you can assess this using the live histogram. You ensure the camera levels are about 75% filled. Gain should be quite high. You capture a video between 30 and 60s length as an SER file, then align in AutoStakkert! using the ‘surface’ alignment function and a grid of alignment points, then select say the best 50% of frames to stack. You can then sharpen the image in another program, or try the sharpening function in Autostakkert!.

One thing I do which I find is beneficial is to use an IR-pass filter on the camera (either in a nosepiece or a filter wheel) in addition to the objective solar filter. (I don’t have the Seymour, I have Thousand Oaks). This steadies the seeing. The result will be a red image. Other people use the Baader solar continuum filter (which is green). Basically you will always improve the seeing by excluding blue light. You can capture the data in FireCapture in mono (no de-Bayering).

Best of luck.

[Daryl Dobbs]

I haven’t managed to try this out but I’ve heard Focus Magic is useful.

Focus Magic – Sharpen Your Blurry Images and Photos

[Tony Laverick]

Thanks. That’s useful information.

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