Solar Imaging

White light solar observation or imaging uses exactly the same setup as lunar imaging, with one very important addition. You have to put a solar filter in front of the telescope to reduce to a minimum the amount of sunlight entering the telescope. You have to reject 99.999% of the light and heat energy or you will cause irreparable damage to your eyes and equipment.
There are several makes of solar filter on the market. The one I use most of the time is Baader astro solar film; you can buy it in a ready-made cell or just buy the film and make your own cell to hold the film. The important thing when making your own cell is not to stretch the film. I also use a Seymour solar filter but you have to be more careful with this as it’s made on a glass substrate and will break if dropped.
These filters are relatively inexpensive and give you the means to experience the sun’s dynamic surface which changes from hour to hour, sometimes from minute to minute when a flare occurs. In this respect the sun is far more exciting to observe, unlike the moon with its static features. There is also the Herschel wedge that uses a special prism to reject that 99.999% of light and heat and fits at the back of the telescope, so you do not use solar film in this case.
Never look at the sun when aiming the telescope at it. Yes this does sound like a daft statement, how can you point something at something else without looking at it. The answer of course is to use the telescope’s shadow. When the shadow of the optical tube is round you’re pretty well aimed at the sun.

Never use the finder scope unless that too has a solar filter on the front of it. If not it’s better to remove it altogether, especially if it has no front cover or you will burn out the cross hairs.

When solar observing or imaging, you will have to focus on the sun’s edge or limb so it appears sharp, and then focus on any sunspots until they are as clear as you can make them. You can see the Umbra and Penumbra of sunspots and the rice – like granulation on the boiling surface.
Image capture is the same as lunar imaging using Firecapture and Registax.

Sun light is made of all the colours of the spectrum. These are the visible wavelengths of light. Also there are the invisible wavelengths that we can’t see, from the Ultra Violet bottom end of the spectrum to the far Infra Red high end of the spectrum.
The crimson Hydrogen alpha ( Ha ) light at 6562.8 Ångstroms (656 nanometres) is what interests me. This is the narrow slice of the sun’s spectrum where filaments, flares, spicules and prominences become visible. It’s a constantly changing scene, that brings to life the fact that the sun is a nuclear furnace.


The equipment used for Ha viewing and imaging is fundamentally different from white light viewing and imaging and it’s far more expensive. There are dedicated Ha telescopes that can only be used for Ha solar work ranging in cost from £900 to almost £28,000. There are modules that can be used with ordinary telescopes to convert them into Ha solar scopes. Companies like Lunt, Coronado, Daystar Instruments and Solarscope make these modules – again the cost is over £1000.
I use a Daystar Quark ( Chromosphere model ) that was purchased second hand for £650 and has served me well for a few years now. It goes into the back of the telescope like an eyepiece and the eyepiece or camera inserts into the back of the module. Again, image capture is the same as for white light imaging using Firecapture and Registax.


A note on Newton’s Rings – some cameras suffer from Newton’s Rings, banding lines visible in the image. This is caused by reflective interference between two flat surfaces, in this case the back of the Quark and the front of the camera sensor. Removal of these lines is possible by means of tilting the camera with respect to the Quark. I use a tilt adapter from Rowan Astronomy as it completely eliminates the interference pattern.

 

 

 

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