Stitching!

I now write a regular piece for the Eddington Astronomical Society, setting out what’s going to be on view in the night sky each month. In all honesty, it will probably lean towards astrophotography!  You can see the March 2014 version here.

One of the opportunities identified as coming up in March was the view of Jupiter reaching its highest point in the sky, elevated 59° in the early evening of the 13th. This looked like a challenging photo project, with bright Moon, bright Jupiter, bright and faint stars and the inevitable Morecambe Bay glow. It would also be at its best during twilight.

Sadly the Cumbrian rain was forecast for that evening, but we enjoyed a few days of high pressure just before then, with a couple of clear nights.

On Tuesday, 11th March, I strolled up to the Mushroom on Scout Scar with no more than camera and tripod. The 18-200mm zoom is pretty wide at 18mm, but I wanted a field of view of about 150°, so I set it to 24° and took nearly forty frames in a grid pattern looking south.

Photoshop can stitch shots together to make panoramas, but it needs clear points of reference in the shots and can only run on automatic. So, if it can’t identify the overlapping shots itself, there is no option for user-intervention. It simply doesn’t work on night sky mosaics.

That’s when I found PTGui, a programme that does exactly the same, but with a much wider range of projection options and, most importantly, the facility for the user to identify the overlap points (ie the stars) manually.

Here is the result, the view south from Scout Scar, Tuesday evening13th March. The sky isn’t flat, of course, and stitching frames requires distortion according to various rules depending on the projection settings. Circular projection seems to give the best compromise on distortion, then I cropped the result to a nice tidy rectangle.

All frames ISO 1600, 10 seconds 24mm f/5.6.

Big sky!  Nearly 40 frames stitched in PTGui, each 10 sec ISO 1600, 24mm f/5.6

Big sky! Nearly 40 frames each 10 sec ISO 1600, 24mm f/5.6, stitched in PTGui

Total lunar eclipse of December 2010

6am, Tuesday 21 December 2010, I arrive on Scout Scar.  Minus 15 degrees might have been optimistic.  Camera, lenses, tripod, everything I can wear, plus a flask of hot ribena. All you need to know about when and where to see an eclipse is available from the Mr Eclipse website maintained by Fred Espinak.  I am deeply indebted (as many amateur astronomers must be) to Mr Espinak for the solid, reliable information that he chooses to share with anyone who cares to go and look.  Here are the details he provided for the 21 December 2010 lunar eclipse.  Totality will be at sunrise in Cumbria, which means the Moon will disappear into shadow and into light at the same time.

Earth shadow

500mm f/8, ISO 400, 1/640 sec.

At 7.02, the Earth’s shadow is obscuring half the Moon.  Despite the rehearsal, I cannot find reliable focus at 1000mm, so have to be content with 500mm.

500mm f/8, ISO 400, 1/60sec.

500mm f/8, ISO 400, 1/60sec.

As the Earth’s shadow moves across the lunar surface, the remaining illuminated area moves into penumbra – partial shadow – and the exposure has to be increased to compensate.  Here the exposure is around ten times the previous photo.

500mm f/8, ISO 400 2 sec.

500mm f/8, ISO 400 2 sec.

A further increase, this time by a factor of 120, reveals the shadowed part to be illuminated by light that has passed through the Earth’s atmosphere, giving the Moon a red glow.

500mm f/8, ISO 400, 1/30 sec.

500mm f/8, ISO 400, 1/30 sec.

Approaching totality, the last sliver of illuminated surface is in penumbra and a further increase in exposure is required.

500mm f/8, ISO 400, 3 sec.

500mm f/8, ISO 400, 3 sec.

As the eclipse becomes total, the Sun is rising behind me.  The sky is getting lighter and the image is becoming flat, showing almost no contrast. With the extreme cold, the flat, dim lighting and the awkwardness of focusing the 500mm lens, I have enjoyed watching the eclipse more than I have enjoyed photographing it, to be honest. However…

105mm f/5.3 ISO 1600 1/2 sec.

105mm f/5.3 ISO 1600 1/2 sec.

… almost as a last resort, I switch to the Nikon 18-200mm zoom lens (and switch the D90 to “Auto”) in the hope of capturing something of the context for this morning’s efforts.  Once again, the D90 does exactly what I ask of it, and “Total lunar eclipse over the Langdales” has become one of my favourite shots of the Moon.  Just a tiny warm up and a little extra saturation in Photoshop.

Rehearsing for the eclipse

27mm f/4, ISO 1600, 5 sec.

Less than 24 hours to go and I’m on Scout Scar, checking conditions for the eclipse the next morning.  Under a full moon, the “Mushroom” is as bright as day – only Orion in the background betrays that it is 9pm in December.

Full Moon 500mm

500mm f/8, ISO 400, 1/2000 sec.

The Moon looks good through a Nikkor 500mm reflex telephoto, but this lens does not have a “hard stop” when focused at infinity, so focus adjustment is by eye.  As this involves rotating the full barrel of the lens, it is very trying.  There is no easy fine-tuning, and the aperture is fixed at f/8, so there’s no stopping down for depth of field.

The most productive option is to use the “Live View” display on the D90, which can be zoomed and panned while focusing.  That can’t be done while wearing gloves, however, and it’s already well below zero.  Tomorrow morning is forecast to be minus 15.

Full Moon 1000mm

1000mm f/16, ISO 400, 1/800 sec.

With the Sigma 2x converter, the lens doubles up to a 1000mm f/16.  Focusing difficulty doubles up too.  I’m never really sure whether it’s in focus at 1000mm.  Perhaps the image is slightly soft, even when in sharp focus.

Contrary to expectations, the Moon isn’t an inspiring subject when full.  The light is just flat and there’s no detail.