Introduction

I have a keen interest in astronomy but am not much of an astronomer. Occasionally, if there is an important and accessible celestial event in progress, I'll take some photographs of which the ones presented here are examples.

Moon

The moon is an easy astronomical subject. It's big, has lots of interesting detail and is bright enough for handheld shots. The most impressive images are obtained when the sun strikes at something of an angle as in the waxing gibbous here. This produces shadows which act to highlight detail. By comparison, a full moon shows considerably less relief and is a rather bland subject.

Equipment: Nikon D7200 with Nikkor 200-500 mm @ F/8, 500 mm

2017, August 21st Solar Eclipse

This was a spectacular event with clear skies over much of North America. Here in Calgary we had approximately 80% totality. Not having much experience of solar eclipses a couple of things proved unexpected:

• It didn't get nearly as dark as one would think with 80% of the sun obscured. In fact, a lot of people uninterested in the event claimed they didn't even notice.
• It was a hot day but the air cooled dramatically to the point of feeling chilly by way of contrast. I noted a temperature drop of more than 10 or 12 degrees Celsius - down to 18C or thereabouts from a high of 28C. The effect was probably exaggerated because of my elevation at 3800 ft.

Equipment: Nikon D7200 with Nikkor 200-500 mm @ F/8, 500 mm with solar shield.

It's absolutely essential to shield eyes and equipment from the intense solar radiation. I ordered two sheets (one a spare, in case I ruined the first one) of aluminized Mylar made for this purpose from Amazon. The stuff is somewhat expensive at over $30 for a 10 inch square piece but you have to have it. Two pieces of photographic matte board were then trimmed to size and a circular hole same diameter as the front element of the telephoto lens cut through them with a fly-cutter mounted on a drill press. This is a tricky operation. You have to glue the matte to a piece of wood, gluing only the central portion which, when removed, leaves the hole in the matte, the latter then coming free. Clamping has to be absolutely rigid as the fly-cutter exerts an unbalanced force on the work-piece. Initially, give the cutter a turn by hand to ensure it won't strike anything such as the clamps. Advance the cutter very slowly so as not to snag and tear the matte. I was very pleased and a bit surprised to obtain a perfect cut through both pieces of matte. The material is quite dense - more like soft wood - which contributes to its surviving the operation.

A piece of the Mylar was then sandwiched between the two pieces of matte (subsequently taped together at the edges) to cover the hole and a collar to fit the lens fashioned from a scrap of Armstrong "Cushion Step" flooring fastened in place with "Gorilla Glue". The inside of the collar is lined with black felt to provide a snug friction fit. Getting the collar circular and the right diameter is simplified by using the lens itself as a template. Set it front down and centered on the matte sandwich, then wrap the collar strip (with Gorilla Glue already applied) around and secure it with a rubber band after trimming to exact circumference. You don't want to get glue on the lens so put something under to raise it a small distance above the matte sandwich. Needless to say, the lens cap should be in place. Leave the lens as it is until the glue has set and you are good to go.

Somewhat counter-intuitively, it isn't necessary for the Mylar sheet to be optically flat or, indeed, very flat at all. A few wrinkles and bulges make no difference. That's because the material is very thin and has a low refractive index. The mounting method used here does, however, produce a very flat surface that looks great. Some observers just secure the material over the lens with a rubber band but that's not the sort of "craftsmanship" you can take a lot of pride in or show-off. To each his own. The quick-and-dirty method works.

Two photos of this aparatus are included.