Geminid 13 Dec 2014

[MarkS]

A Geminid streaks past Orion last night (13 Dec 2014)

I left the Canon 600D on a stationary tripod continuously taking 15 sec exposures at ISO 1600 with the 18-55mm kit lens set to 18mm and F5.6
This single exposure was the best of the bunch - shown scaled and cropped.  Note that the streak near the bottom is an aircraft



Mark

[JohnP]

Nice. Well done on capture.. better than me. John

[MarkS]

I have a few other Geminid images as well but that one, next to Orion, was definitely the most photogenic.

I don't like the noise characteristic of the 600D sensor.  The raw images have lots of noisy pixels that come and go from frame to frame.  As a result, the darks do very little to remove them.  So I had to use very restrained processing on that image to keep those noisy pixels in check. I was storing both RAWs and high quality jpegs so I could tell that the in-camera processing for the jpegs removes those noisy pixels but at the expense of leaving a background full of coloured blotches.

The camera body completely iced up with frost so I'm glad I used the dew heater on the lens!

Mark

[JohnP]

Hi Mark,

Yes it is quite noisy. I have a little Canon compact & managed to override the camera settings using Canon Hack software. I was pleasantly surprised with outcome. Below single 45 sec exposure (jpeg) - camera sitting on garden table ISO 100 from Bromley's crappy skies - No filters... I might even try a few tracked images with it (piggyback on scope).. I can also save raw & have option for subtracting in camera dark as well...

[RobertM]

Good capture Mark and well framed.

Noise is what you expect on these cameras.  I would hazard a guess that the random nature is down to amplifier noise in the electronics so it could occur at random anywhere on the frame.

Nice image anyway.

Robert

[JohnP]

So why's it so much noisier than little compact?

[Mike]

The compact will have smoothing algorithms which are great, but which also destroy data. You will probably find it eats stars and little gas clouds, etc.

I caught about 4 or 5 Geminids on my Nikon D7000. I'll post them up later.

Mike

[JohnP]

Hi Mike, agreed - I realize that but my little compact also saves Raws .cr2 & they look just as smooth - in fact in raw viewer they look better than Jpeg as no compression artifacts...

John

[RobertM]

John,
Some of those compacts have very low read noise so that may have something to do with it.  There may even be less thermal noise as the sensor is small and most of the heat could get dissipated quite quickly through the smaller body.  Note also that Mark was shooting for a while and giving the sensor time to warm up.

Just guesses really - unless you characterise your camera we may never now.

Robert

[JohnP]

Hi Robert, that makes sense.. twas a cold night as well.. I was using camera for say around 20 min or so.. also only iso100 anything faster and images started getting too bright...

[MarkS]

I've looked again at the noise and it is definitely read noise but it does form a nice "bell-shaped" distribution without any worrying distinctive features.  In comparison, the thermal noise is almost non-existent - as expected for short exposures, especially since the camera was covered in a layer of heavy frost that night.  The whole landscape was white the following morning - best frost of the year.

The maths shows the read noise to be around 2.6e (ISO 1600) which is as expected.  Sigma stacking a few exposures together gives an impressively "clean" image.  I'll post it later.

Mark

[MarkS]

I've stacked another seven 15sec subs into the background to reduce the noise:



A less cropped version is here:
http://www.markshelley.co.uk/Astronomy/2014/geminid20141213v2.jpg

Mark

[Mike]

Here is one I caught...

[JohnP]

Nice mike..

[MarkS]

Nice, Mike. That must have been pretty bright.  I quite like the cloud in the image.