Sony A7S - A game changer?

[MarkS]

I'm following Robert's lead and my Sony A7S is now on order.
http://forum.orpington-astronomy.org.uk/index.php?topic=10177

I got the opportunity to do a whole batch of technical testing on it (thanks Robert!).  From those results I conclude this camera  really is a game changer for astro-photography.  Here's a good review of it.
http://petapixel.com/2014/07/30/sony-a7s-astrophotography-review/

I'll present my batch of results later.

Mark

[Kenny]

Looks awesome. Way above my pay grade. #mustgetajob 

[JohnP]

Look forward to seeing your pictures/ results - what delivery date they giving you  - I presume you are going for the full Ha modded version...


........Fay - You know you DON'T want one...

[Fay]

I might!!!!

[The Thing]

I want one! Saw Robert using his at Cairds DSC and it was as advertised, a really nice astro image - on the LiveView! Got a house build to pay for first though

[MarkS]

Look forward to seeing your pictures/ results - what delivery date they giving you  - I presume you are going for the full Ha modded version...

It should arrive next week.  I'll then do some further experiments and imaging with it before I DIY mod it.

[JohnP]

Blimey Mark you are brave... ru going to mod yourself or are you on about sending it off...?

[JohnP]

Fay, anybody that's not well deserves to buy themselves a new toy and you can't count the Star Adventurer because that was ordered before you were ill....

[MarkS]

Blimey Mark you are brave... ru going to mod yourself or are you on about sending it off...?

DIY mod of course!

So, here's my explanation of why I think this is a game changing camera - all based on measurements I've done.

As you know, I currently use a modded Canon 350D, so my comparisons are based on that.  I also have a SX M25C - a cooled one shot colour camera.  Its quantum efficiency is only 1.1x that of the 350D which is hardly any different.  I rarely use it except for when I need the cooling.

The Sony A7S is a 12Mpixel full frame camera, so the pixels are big - similar to an Atik 11000.  It has an Exmor sensor whose QE is 2x that of the 350D for H-alpha and 2.3x for Green and Blue.  Sensorgen gives it a QE of around 65%, which sounds about right to me for peak green response. The area of each pixel is nearly twice that of the 350D which together with the high QE means each pixel collects 4x as much light as a 350D pixel.  The read noise is 1.6e at a typical astroimaging ISO of 2000-4000 (unit gain is around ISO 4000).  So the read noise is insignificant and the dark current per pixel is 1/3 of the 350D.

The result of all this is that even at Kelling Heath where the skies are pretty dark and imaging with a scope as slow as F6 then the sky background noise will always be greater than the combined thermal noise and read noise for all ambient temperatures of 20C or less.  So cooling is not required for almost all UK imaging conditions!  Under these conditions the Sony A7S should produce visibly superior results to any of the present generation of cooled OSC cameras. It's cheaper than almost all of them, needs no external power supply etc.

You will recall that I nearly bought a Sony A5100 or A6000 (they use the same Exmor sensor as each other).  The QE of these was not as high as the A7S and the thermal noise was significantly higher - probably due to having 24Mpixels crammed onto an APS-C sensor.  So you would still need a fairly fast scope in order for the skyfog to outrun the thermal noise on a warmish evening.

As always, the proof will in in the images it produces - so watch this space ...

[Fay]

If ever im sent into space, I hope I have Mark with me   

[JohnP]

Are there online destructions.. I mean instructions for modding the camera...? Taking a screwdriver to a pristine £1500 Plus camera would fill me with dread...!

[RobertM]

Are there online destructions.. I mean instructions for modding the camera...? Taking a screwdriver to a pristine £1500 Plus camera would fill me with dread...!

It's not quite the same as modding a Canon Fay, much less plastic plus there's better engineering gone into it.  Even so you've got to be quite determined that it's the right thing to do.  If Mark and I were in in the opposite scenario then I'd want to do the same.

Robert

[JohnP]

It's not quite the same as modding a Canon Fay

Cheers Roberta... since when have you started calling me Fay...!!!!!!!!!!!

[RobertM]

Oops... Sorry John, I don't know how that happened - you don't even look like Fay

Please accept my apologies.

Robert

[JohnP]