Sunday, November 25, 2012

Some more backyard astrophotography with Sigma 100-300mm f4 and D800

There have been four (not too many) clear nights after last post on the subject. I've imaged M45 and M31 with its sister galaxies using Astrotrac tracking device and Sigma's 100-300mm f4 telezoom on a Nikon D800 DSLR.

Here is Messier 45 or Pleiades at 300mm after some heavy cropping. Twenty four images at ISO800 and 30s each were stacked together. Contrast was boosted in GIMP 2.9, which handles 16bit files but is just too slow for general use - yet. However, the nebulosity is well shown even with all the light pollution in the sky.

By the way, one cheap way to reduce light pollution when using a unmodified DSLR is to use a redhancer filter. It's exactly the same filter as the expensive Baader one but comes in bigger sizes such as 77mm. Baaders are limited to 2" or around 50mm. The filter works because there's neodymium element blocking the wavelengths that high pressure sodium vapour lamps emit. Most of the orange glow in the sky is gone with such a filter.

Messier 45 with D800 and Sigma 100-300mm f4

And here's another take at same subject, now with 40 images stacked together. There's less noise and more detail when compared to the earlier attempt. I'm pretty satisfied with this one.

Saturday, November 24, 2012

Explosion in the sky - northern lights in Maaninka

A week or so back, I was photographing M45 (Pleiades) when I noted a bright green band in the northern sky. Northern lights were suddenly active. So off to Maaninka we head since the skies are darker there. We were greeted by this band of green and red(!) lights as soon we stepped outside of the car.

Revontulia 2012-11-13

I used mostly the Samyang 14mm f2.8 on a D800 to shoot these. Exposure times were in the 15 to 30 second range and ISO was 1600. As the aurorae became more active, the exposures were shortened to avoid blurring details from the bands.

Revontulia 2012-11-13

There's quite a bit of spherical aberration in the centre of the image up until f4 or so. Bizarrely it goes away in the corner of the frame. Strange lens I must say.