With it being this time of the year, the chances of Kendal receiving its annual hour of sunshine means that astronomers can turn from the cold, cloud covered and all too brief summer nights to the cold, cloud covered and all too brief glimpses of the summer sun. As it happens, I have a few bits of new equipment that may help capture this rare event.
First up is the new T-ring. This is a screw-thread that has been specifically designed to fit onto my SLR where the lens normally goes. It has to be tailored to the camera as different companies have different lens fittings. Once the ring is on the camera, an adapter can be screwed into it that then allows the camera to be slotted into the back of a telescope. The one I use is my 60mm Tasco, which has an 800mm focal length, ten times the maximum of the camera’s native lens. The result is the Moon filling more than a small dot in the frame of a picture, but sadly I can’t put the result up yet as it is a film SLR…
The Tasco isn’t much of a telescope – 60mm is a very small aperture, which limits it to a maximum magnification of 120x in perfect skies and 60x in normal skies due to the diffraction limit – but it does the job so far as focusing for a camera goes. Newtonian telescopes don’t normally have sufficient inward travel for the focus, though Cassegrains are good imagers too. The Tasco’s day job before the arrival of the T-ring was something else refractors tend to be preferred for – solar observing. In this case, projection of the solar disc onto a metal plate that slots onto a rod that protrudes out the back. But another recent purchase has rather put that out of contention.
The AstroZap solar cap is a ring that fits onto the end of a telescope and covers the aperture with Baader solar filter paper. This is essentially one of those eclipse glasses made up for a telescope (both my eclipse glasses and this cap have a Neutral Density rating of 5). It produces a bright white disc, which retains much of its details even in thin cloud, unlike the projection, which vanishes at the first suggestion of a haze. Being on a telescope, details can also be zoomed in on and as I’ve stuck it on the 130mm Celestron SLT, the image has a higher resolution than the 60mm Tasco can produce.
Before an image can be taken, the telescope has to actually point at the Sun. But how is this achieved when there is no way to look through the thing and the finderscope is also out of action? The answer is to use the shadow of the telescope. If the Sun is looking directly down the barrel, as it needs to, then only the shadow of the barrel, a nice black circle rather than a line or an oval, should be visible. At this point, then start jigging the telescope about to get the fine adjustments – in the case of projection, do this while looking at the thing the projection should shine on, in the case of a filtered telescope, do it looking through the eyepiece, making sure you have first checked the filter for holes before putting it on the telescope.
Once in place, the image was focused, showing the disc of the Sun and one prominent sunspot, which easily showed its umbra and penumbra. Zooming in with the other eyepieces showed little further than confirming what was there. I took a close to full disc image afocally, using the digital camera at 10:50am on the 30th of June. No prominences were seen or expected as in white light, they are drowned out by the disc of the Sun. An eyepiece filter would be required to get that sort of view.
On twitter, there were noises about various effects caused by sunlight passing through ice crystals in the late evening. This provided a range of effects including Sun dogs (fake Suns either side of the real ones) Circumzenithal Arcs (small, intense rainbows above the Sun) and the like. Sadly, the haze set in here so hard the sky turned a blank white and the Sun vanished, so I missed out on all of that.