Constellation Portraits 50mm Astrophotography

Orion

click image

Taken under mag 3.5, light-polluted skies, in the middle of Quezon City. I was amazed that the image captured star almost to magnitude 11 with just 4 seconds exposure. Knowing that 4 second sub-exposures will have low signal to noise ratio, to partially compensate I took lots of frames (41) for stacking to improve the s/n ratio.

Why 4 seconds and not 60 or 300 seconds? Well I'd love to shoot that long, but I don't have a tracking mount yet, I was shooting with a fixed tripod. And 4 seconds with a 50mm lens near the celestial equator where the stars have the fastest apparent motion, is the longest exposure with no star trailing when viewed at 100%. There are formulas for computing the maximum exposure time for a given focal length and declination, before star trailing becomes apparent. But its simpler and more fun for me to just experiment with different exposure times from 1 to 15 seconds. Nearer the the celestial poles where stars have the least apparent motion I can get away with 5-6 second with not to much trailing.

Motivated by the reasonable result of this, I plan to do a series of constellation portraits as I wade my way to the deep waters of astrophotography. I am also planing a series of short essays of the subject images posted here.

Image Data

Optics: Tamron 17-50mm f/2.8  set at 50mm f/2.8

Camera: Canon EOS X5 DSLR (unmodified)

Mount: Fixed Tripod
Exposure: 41 X 4sec at ISO 1600 RAW

Calibration: Darks, Flats,and Bias in DeepSkyStacker by Luc Coiffier

Processing: Gradient removal in Iris by Christian Buil, levels, curves, color in PS

Location: Quezon City, Philippines

Date Time: February 10, 2012. 7:30-8:00pm PHT

Conditions: 27C, 70RH, partly cloudy