M51 Whirlpool - with newly modded Sony A7S

[sharkmelley]

I've repeated my M51 image (http://stargazerslounge.com/topic/242439-m51-whirlpool-first-light-with-sony-a7s/) but this time the Sony A7S is DIY full spectrum modded - so a Baader IR/UV cut filter was used.   As before Sony A7S full-frame mirrorless camera on a Celestron C11 with 0.8 reducer/flattener i.e. imaging at F8.  A total of 2 hours of data in 90sec subs at ISO 2000 was taken.  Again the subs were kept short to overcome a flexure or mirror shift problem I was experiencing but the short subs have has not affected the image quality because of the remarkably low read noise at ISO 2000.  The sky quality was slightly worse at 20.8-21.0 and the temperature slightly higher 8C.

This is a crop of the image because I still haven't got the flattener adjusted to my satisfaction:

The full size (i.e. 1:1 scaling) of the crop can be found here:

http://www.markshelley.co.uk/Astronomy/2015/m51_a7smodded_20150512.jpg

The only processing I've done is to perform a straight sum of the 80 calibrated frames, an arcsinh stretch of the luminance channel (in IRIS), RGB balance (I had to keep the tone down the red channel) and a slight colour saturation.

As before, the light pollution is by far the greatest contributor to the background noise.

Mark

[michael.h.f.wilkinson]

Superb

[ultranova]

Looks like the camera is performing very well indeed,

Nice shot

Paul

[MartinB]

Looks like you've got a good amount of signal.  Is is a little out of focus?

[sharkmelley]

Looks like you've got a good amount of signal.  Is is a little out of focus?

It might be a little out of focus.  But the seeing was only average and that also affected my guiding.  I also haven't applied any kind of deconvolution yet - that will help to tighten things up.

Mark

[NickK]

Nice Ha dust appearing to the left - I got these with the 414ex at 1h20 with 30 second exposures on mono.. what you get is a full colour image - so it shows how good an OSC camera the A7S is for astro. Personal nitpick about all OSCs is that they loose some resolution compared to mono but if you drizzle each colour plane, you should recover some additional detail anyway to give a halfway house between OSC and mono.

The A7S is certainly a disruptive camera in the mainstream market especially for EAA. Brings DSLR into CCD territory!