M51 Whirlpool again - this time with the Sony A7S modded

[MarkS]

Modded Sony A7s on Celestron C11 with 0.8x reducer flattener.
2 hours of data in 80 x 90sec subs.
Processing has been minimal to show the quality of the data:  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 this time) and a slight colour saturation.



A 1:1 scaled crop can be seen here:
http://www.markshelley.co.uk/Astronomy/2015/m51_a7smodded_20150512.jpg

The thermal noise and read noise are so low that even in with my fairly dark sky (SQM 20.8-21.0 during the imaging session) the light pollution is still the main contributor to the background noise level, even with such slow (F8) optics.

Tonight it goes on the Tak Epsilon at F2.8   

Mark

[Fay]

90secs, what a great result Mark!!!! did you do darks and flats?

[MarkS]

Yes - darks and flats as usual.

Mark

[Mike]

It is certainly looking to be a very capable camera. I wonder how it would stack up against a cooled CCD with a similar sized chip.

[Kenny]

Stuning image Mark.

What do you think is happening on the left of the galaxies? The nebulosity seems to stop rather abruptly.

[The Thing]

Now I really want one!

[MarkS]

It is certainly looking to be a very capable camera. I wonder how it would stack up against a cooled CCD with a similar sized chip.

A very interesting question!  I think the A7S would beat a similar sized cooled OSC because of it's high QE and very low read noise and thermal noise.  Even though it is uncooled, the thermal noise is so low that you can do a 10min exposure before its noise reaches the read noise of a typical OSC camera.  However, a cooled mono camera would still beat the A7S for colour imaging because LRGB is much more efficient than Bayer matrix RGB for imaging.  Additionally the mono has a huge advantage for narrowband.

For short exposures, the A7S will be streets ahead of both cooled mono and OSC because of the crazy low read noise.
Also compare the price of the A7S against a cooled mono camera - that was definitely a huge attraction for me.  I could buy 2 of them and still have plenty of cash left over compared with a full frame astro CCD.

What do you think is happening on the left of the galaxies? The nebulosity seems to stop rather abruptly.

Dunno - it's interesting isn't it.

Now I really want one!

Mark

[Carole]

The nebulosity seems to stop rather abruptly.

That is normal for this galaxy Kenny.  Look at my image of the same object in this month's calendar page.

Carole

[JohnP]

Nice Mark.. very good for quick test at f8.  Can't wait to see result with Tak.. process still looks a tad too red to me... John.

[MarkS]

Yep - a bit too red.

[MarkH]

Mark , well done that is one of the best images of m51 I have seen, awesome!

[Kenny]

The nebulosity seems to stop rather abruptly.

That is normal for this galaxy Kenny.  Look at my image of the same object in this month's calendar page.

Carole

All the nebulosity is rounded in shape but down the left it's almost linear. That doesn't appear 'normal'.

[Carole]

Don't know what you are talking about then Kenny, looks normal to me.

Carole