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  #21  
Old 08-11-2014, 12:52 PM
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Quote:
Originally Posted by mithrandir View Post
Rod, the mate doesn't use darks. He is an experienced astrophotographer and reckons the a7s doesn't need them at 6400.
Never questioned "No darks" Although, the image could probably benefit from their inclusion. "No Flats" however, I wouldn't think that is correct for a full frame sensor on a hyperstar lens. The hyperstar is design for chip diagonal <27mm If you go any larger then severe vignetting is produced by the lens. Having said that, larger sensors can and have been used (See here Image using Hyperstar/Atik11000) but only corrected with excellent flats.

I will also back flip and say that Fritz didn't use flats as it looks like he has cropped his imaged, a lot.

Last edited by Rod771; 09-11-2014 at 09:13 PM.
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  #22  
Old 08-11-2014, 07:51 PM
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here's a good 'real world example', though again the exposures are very quick, at 15-20 seconds, ISO 10,000-12,800

https://plus.google.com/photos/10528...58297874386881
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  #23  
Old 09-11-2014, 10:17 AM
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This is a full frame 12.2 mp sensor, meaning it has large pixels, over 9 micrometers, thus offering relatively high sensitivity.
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  #24  
Old 09-11-2014, 10:46 AM
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Not sure where "over 9 microns" is coming from. My searching has produced a pix size of 8.4 microns.

Strange that Sony does not seem to want to publish this info. It's not on any spec sheets.

Peter
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  #25  
Old 09-11-2014, 11:12 AM
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Hi Peter,

You are right, pixel size is 8.4 and not 'over 9'...

http://www.sony.net/Products/di/en-u...rview/spec.pdf
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  #26  
Old 09-11-2014, 11:56 AM
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Originally Posted by Slawomir View Post
Hi Peter,

You are right, pixel size is 8.4 and not 'over 9'...

http://www.sony.net/Products/di/en-u...rview/spec.pdf
But your point is still valid - the imaging/sampling geometry accounts for most of the sensitivity shown in the M42 - and also the relatively low resolution/image scale. As Sam pointed out, under suburban skies with an f7.5 OTA, you would need >200 hours to get the same M42 SNR with that camera - so it is not just the camera.

None of this is to say that the camera is not very sensitive/low noise - it definitely seems that it is. However, that is by no means the whole story.
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  #27  
Old 09-11-2014, 01:47 PM
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None of this is to say that the camera is not very sensitive/low noise - it definitely seems that it is. However, that is by no means the whole story.
That's why I posted Fritz's comments in whole. Context is important.
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  #28  
Old 09-11-2014, 01:57 PM
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Would like to see it used on an 8" f4 or f5 so it's easier to 'visualise' the camera's ability.
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  #29  
Old 09-11-2014, 02:37 PM
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So surely, there's got to be someone lurking in this thread with disposable income to take the plunge and buy/test one ?!?

Or are we all sitting here dreaming
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  #30  
Old 09-11-2014, 03:32 PM
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Would like to see it used on an 8" f4 or f5 so it's easier to 'visualise' the camera's ability.
You can probably scale it reasonably well Russell. For an 8 inch f4, the image scale and sampling would be reasonably similar, so the time taken under dark skies to get that sort of M42 image would be around 5 hours. Under bright suburban skies it would possibly be 50 hours.

Last edited by Shiraz; 10-11-2014 at 05:01 AM.
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  #31  
Old 09-11-2014, 07:12 PM
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Thanks for the links to Brian's pics Andrew, I'll contact him and get more details.
Brian must have noticed my post. Here's the reply he sent me, with a couple of edits for correct typos:
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I saw a reference to one of my A7S albums on [IIS]. Since Iím not a member and can't respond directly I thought Iíd drop you a note.

Iíve had the A7R since Nov 2013. Used it for about two months unmodded then had it modded to full spectrum.

Iíve had the A7S since it was released in Canada, ~ July 2014. I used it unmodded for three months. It is now also modded to full spectrum.

I use both cameras for astrophotography, nightscape photography, IR photography and daytime photography with various different filters; both clip-in and front mounted.

I tend to use the A7R, with its higher resolution, for wide angle imaging and the A7S for longer scopes and targets that require a touch higher ISO. My cutoff is about 500mm focal length which sort of equates to 1.5-2.0 arcsec/pixel, although I do like the A7S with all of my wide angle lenses when I want to shoot something like the Aurora Borealis handheld or in video, and it is quite possible to shoot handheld under moonlight (which I still find quite amazing!). I also love the A7S for indoor, low light shooting w/o flash and in silent mode.

The A7S outperforms any OSC camera I've ever owned; several DSLR's, a QHY8, QHY8Pro and QHY9C. It is pushing my mono CCD but I can't come to any conclusion on this until I've done some additional testing. I've just starting testing the A7S with an Ha filter at present. In one aspect it already outperforms my mono CCD and that is exposure times. With the ATIK 428Ex I'm looking at 5-20 min. exposures. With the A7S and same scope configuration Iím looking at 20-30 second exposures. This makes a HUGE difference in requirements for polar alignment, tracking/guiding, flexure considerations, whether I use an EQ or Alt-Az mount or a tripod, etc. In fact, I haven't used my guide system since I purchased the A7R last November. Shooting full imaging sessions in 15-20 minutes on a target also agrees with the weather on the eastern slopes of the Rockies, i.e.: weather can change drastically in 20-30 minutes; clear sky to rain/snow .

I have a large number of both A7S and A7R albums and images on Google+ at:
https://plus.google.com/photos/11626...9398213/albums
A lot of the images in the above albums are testing, i.e.: what can the camera do under moonlight at ISO200000?, what kind of noise do I get at ridiculous ISO's, how good is video quality, ad nauseum. So a lot of the images are not show quality... you see the good, the bad and the truly ugly.

Up to this point I've been a pretty solid Canon fan boy. Iím now selling my full spectrum Canon 60D and my QHY8Pro (the QHY8 and QHY9C are long gone). I'll keep my unmodded 60D for situations where I need fast focus, i.e.: wildlife shooting, since the A7's w/ adapters are far from fast autofocus. I already have a Sony FE 28-70mm zoom and have just ordered the Sony FE 70-200mm, f/4 zoom (to gain back a little of that longer fast focus). At present I adapt Canon FD & EF, Pentax, Minolta, Tamron, Sigma, M42 and T2 lenses to the A7R and A7S with what I consider excellent results. Love this capability, specially with the Canon FD lenses which I haven't used since my old FD body cratered years ago and they are great old 35mm film lenses.

Enough said... I am thoroughly enjoying both cameras!

Enjoy!

bwa
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  #32  
Old 09-11-2014, 09:28 PM
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That's great, thanks Andrew, pass on our thanks! I did post to a few of Brian's G+ shots.

As I suspected, this looks a paradigm shift. And I hear JTW will be producing a cooled version!!
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  #33  
Old 10-11-2014, 01:08 AM
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So surely, there's got to be someone lurking in this thread with disposable income to take the plunge and buy/test one ?!?

Or are we all sitting here dreaming
It sounds like a Canon killer. But at that price I won't be buying one unless I win lotto. Might be a bit hard since I don't play lotto.
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  #34  
Old 10-11-2014, 01:53 PM
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JTW have just launched their Christmas offer for the A7s!

http://www.jtwastronomy.com/products..._sony_a7s.html

30 day no questions asked return policy. *struggles to prevent pressing the order button..*
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  #35  
Old 10-11-2014, 02:50 PM
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that price is quite reasonable...
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  #36  
Old 10-11-2014, 09:31 PM
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Yep. I was going to put in an order but some experts told me to wait for a cooled version, as I do like doing the longer subs and also plan to do narrow band. It should be an amazing camera cooled.

But for those who just want to take 1 minute subs, it looks amazing. Can't wait to see future images.
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  #37  
Old 12-11-2014, 06:03 PM
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Here is another review of this camera:

http://www.lonelyspeck.com/sony-a7s-...graphy-review/

and a thread of Cloudy nights:

http://www.cloudynights.com/topic/45...ra-wow/page-15

and some info on DPreview vs the A7R and Canon 5DIII

http://www.dpreview.com/articles/461...non-eos-5d-iii

I am also closely watching developments with this camera and also the Canon 6D Cooled version that may be offered by Central DS as my modified 400D could be due for an upgrade!

Last edited by John K; 12-11-2014 at 06:20 PM.
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  #38  
Old 12-11-2014, 07:55 PM
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The bwallan in that thread with all the a7s knowledge is the guy I've been quoting. I hope at some stage to be well enough to visit him in Alberta.
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  #39  
Old 14-11-2014, 09:43 AM
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Ok, I pushed the button, ordered the modded version from JTW Astronomy. I'll assess its capabilities before getting it further modded as a cooled version. I've put my money where my mouth is, I see a great future for this cam. Obviously I'll post first light images here first.

Canon had better watch out. I just sold my 5D mk III because of Sony's innovation.
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  #40  
Old 14-11-2014, 10:54 AM
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Ok, I pushed the button, ordered the modded version from JTW Astronomy. I'll assess its capabilities before getting it further modded as a cooled version. I've put my money where my mouth is, I see a great future for this cam. Obviously I'll post first light images here first.

Canon had better watch out. I just sold my 5D mk III because of Sony's innovation.
nice work Simon, looking forward to hearing how it performs. It could also be quite a useful planetary camera too...congrats on the purchase
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