Sony A7s II - THE DSLR Killer?

[3kramd5]

The 6D was modded with a "full spectrum" mod, which totally opens the sensor up to as much light as possible by entirely removing all the filters. ...

This all gives the 6D at least a two stop, if not a two and a half stop, advantage...and DESPITE all those advantages over the A7s...the A7s still produced a cleaner image, with more stars, with better colors...

Couple of questions:
1) Why do the two images have different magnification?
2) What do the histograms of the integrated files look like?

One more, possibly a stupid one, but that's fine:

3) If all the filters were removed, weren't the colors added in post (and thus is it fair to really compare them)?

Yeah, as you say still not much to go on. I'm sure it'll perform well at high ISO I'd just like to see it for myself before making any rash decisions.

Here are some raws: http://we.tl/X6ACE5UQem , https://www.dropbox.com/s/ub2jagdhl9blg5x/DSC09049.ARW?dl=0

 

[jrista]

Here are a couple of examples:

http://www.cloudynights.com/uploads/monthly_06_2015/post-205769-0-45448000-1435261812.jpg
http://www.cloudynights.com/uploads/monthly_06_2015/post-205769-0-36074400-1435261831.jpg

The top is the A7s, bottom is 6D. The A7s is 42 minutes of exposure at ISO 1600. The 6D is 60 minutes of exposure at ISO 1600. The 6D subs were gathered under darker skies, by about a factor of 1.6x, which is 1 2/3rds stops BETTER than the skies the A7s subs were gathered under. The 6D was modded with a "full spectrum" mod, which totally opens the sensor up to as much light as possible by entirely removing all the filters. The A7s was only a partial mod, which removed the primary IR cutoff filter, but left all the other filters in place, so there was still some filtering occurring.

This scenario gave EVERY advantage possible to the 6D. The 6D has longer integration time by 43% (half a stop). The 6D was a full spectrum mod so it had no filtering of any kind, whereas with default filtering it doesn't even get 20% of the primary Hydrogen emission, Ha (hydrogen alpha) while the A7s still had it's first LPF filter in place which filteres out some Ha. The 6D was used under darker skies (nearly a pristine dark site, 21.2 mag/sq"), which reduces extra unwanted light signal, which reduces photon shot noise, whereas the A7s was used under skies that had a moderate amount of light pollution (20.0 mag/sq").

This all gives the 6D at least a two stop, if not a two and a half stop, advantage...and DESPITE all those advantages over the A7s...the A7s still produced a cleaner image, with more stars, with better colors, less background noise, and a deeper exposure.

Don't know about anyone else, but that is pretty telling to me. The technology Sony is packing into their cameras, whether all the external factors are perfect or not (lot of people on this forum bring up Sony's plastic mount as a major issue, for example), is truly phenomenal stuff.

Couple of questions:
1) Why do the two images have different magnification?
2) What do the histograms of the integrated files look like?

I don't have the original files, so I cannot say what the histograms look like. The images were processed with PixInsight, and integration radically changes the histograms. Pre-stretch, in linear mode, histograms look all bunched up to the left. Post-stretch, it would depend on the processing to some degree. The thing is, that's all in 32-bit float space, so that has little to do with the camera. A more reasonable question would be what do the histograms of the individual RAW images look like, as that would be closer to the hardware...but I don't have that information either.

The magnification differs very slightly. The image scales were normalized as much as possible, but we don't have zoom telescopes, so getting 100% identical image scales is basically impossible. They are off only by a small fraction, however, and as comparable as two deep sky images can be.

 

[jrista]

The 6D was modded with a "full spectrum" mod, which totally opens the sensor up to as much light as possible by entirely removing all the filters. ...

This all gives the 6D at least a two stop, if not a two and a half stop, advantage...and DESPITE all those advantages over the A7s...the A7s still produced a cleaner image, with more stars, with better colors...

Couple of questions:
1) Why do the two images have different magnification?
2) What do the histograms of the integrated files look like?

One more, possibly a stupid one, but that's fine:

3) If all the filters were removed, weren't the colors added in post (and thus is it fair to really compare them)?

The filters of the filter stack OVER the sensor were removed. The CFA itself as not removed, these were not mon-modded cameras, only astro modded cameras. Astro modding just removes the IR cutoff filters (which these days are built into the low pass filters, so the low pass filters are removed as well), which enhances the sensors sensitivity to the full visible spectrum. Without the mod, red sensitivity is SIGNIFICANTLY diminished.

These sensors were both still bayer CFA sensors, though, still both full color.

 

[3kramd5]

The 6D was modded with a "full spectrum" mod, which totally opens the sensor up to as much light as possible by entirely removing all the filters. ...

This all gives the 6D at least a two stop, if not a two and a half stop, advantage...and DESPITE all those advantages over the A7s...the A7s still produced a cleaner image, with more stars, with better colors...

Couple of questions:
1) Why do the two images have different magnification?
2) What do the histograms of the integrated files look like?

One more, possibly a stupid one, but that's fine:

3) If all the filters were removed, weren't the colors added in post (and thus is it fair to really compare them)?

The filters of the filter stack OVER the sensor were removed. The CFA itself as not removed, these were not mon-modded cameras, only astro modded cameras. Astro modding just removes the IR cutoff filters (which these days are built into the low pass filters, so the low pass filters are removed as well), which enhances the sensors sensitivity to the full visible spectrum. Without the mod, red sensitivity is SIGNIFICANTLY diminished.

These sensors were both still bayer CFA sensors, though, still both full color.

Gotcha. I was really impressed that someone disassembled their sensor subassy

 

[StudentOfLight]

Here are a couple of examples:

http://www.cloudynights.com/uploads/monthly_06_2015/post-205769-0-45448000-1435261812.jpg
http://www.cloudynights.com/uploads/monthly_06_2015/post-205769-0-36074400-1435261831.jpg

The top is the A7s, bottom is 6D. The A7s is 42 minutes of exposure at ISO 1600. The 6D is 60 minutes of exposure at ISO 1600. The 6D subs were gathered under darker skies, by about a factor of 1.6x, which is 1 2/3rds stops BETTER than the skies the A7s subs were gathered under. The 6D was modded with a "full spectrum" mod, which totally opens the sensor up to as much light as possible by entirely removing all the filters. The A7s was only a partial mod, which removed the primary IR cutoff filter, but left all the other filters in place, so there was still some filtering occurring.

This scenario gave EVERY advantage possible to the 6D. The 6D has longer integration time by 43% (half a stop). The 6D was a full spectrum mod so it had no filtering of any kind, whereas with default filtering it doesn't even get 20% of the primary Hydrogen emission, Ha (hydrogen alpha) while the A7s still had it's first LPF filter in place which filteres out some Ha. The 6D was used under darker skies (nearly a pristine dark site, 21.2 mag/sq"), which reduces extra unwanted light signal, which reduces photon shot noise, whereas the A7s was used under skies that had a moderate amount of light pollution (20.0 mag/sq").

This all gives the 6D at least a two stop, if not a two and a half stop, advantage...and DESPITE all those advantages over the A7s...the A7s still produced a cleaner image, with more stars, with better colors, less background noise, and a deeper exposure.

Don't know about anyone else, but that is pretty telling to me. The technology Sony is packing into their cameras, whether all the external factors are perfect or not (lot of people on this forum bring up Sony's plastic mount as a major issue, for example), is truly phenomenal stuff.

Couple of questions:
1) Why do the two images have different magnification?
2) What do the histograms of the integrated files look like?

I don't have the original files, so I cannot say what the histograms look like. The images were processed with PixInsight, and integration radically changes the histograms. Pre-stretch, in linear mode, histograms look all bunched up to the left. Post-stretch, it would depend on the processing to some degree. The thing is, that's all in 32-bit float space, so that has little to do with the camera. A more reasonable question would be what do the histograms of the individual RAW images look like, as that would be closer to the hardware...but I don't have that information either.

The magnification differs very slightly. The image scales were normalized as much as possible, but we don't have zoom telescopes, so getting 100% identical image scales is basically impossible. They are off only by a small fraction, however, and as comparable as two deep sky images can be.

You mentioned the two stacks were shot in different locations, so does magnification change by the latitude where shots are taken? Or does it change due to atmospheric conditions or how close an object is to the horizon maybe or some other reason?

I didn't think of telescopes needing to zoom.

The reason I asked about magnification is that I noticed the 6D stack shot looked smaller than the A7s shot. I guess I expected the 6D shot would be look larger due to the higher native resolution. You also mentioned something called drizzle to increase resolution. Did you use this technique when doing this comparison and can you point me to a good resource so I can read up more about drizzle? Sounds interesting.

Thanks

 

[jrista]

I'm not exactly sure what you are referring to. Magnification isn't talked about much in astrophotography. We are more concerned with image scale, or the number of arcseconds per pixel. Image scale is affected by focal length and pixel size. With the same scope, the image scales with these two cameras would differ quite considerably. The difference in image scale with these two images is actually fairly small. I don't know exactly what scopes were used, but the fact that they only differ by so little is actually fairly surprising. Their image scales have to be quite similar.

Image scale effectively tells us photon flux, the rate of photons incident on each pixel. With similar image scales, the photon flux is similar. That's an "equivalent" (or nearly so) situation in astrophotography. That reduces the comparison to differences in hardware and sky darkness.

Star sizes differ usually because of differences in seeing, which blurs detail. But detail isn't the most important factor we are interested in here. We are interested in how much noise there is, and how deep the exposures are. For similar image scale, and with the 6D having significant advantages over the A7s both in terms of integration time and sky darkness, the A7s image is still BETTER. It's cleaner and has a deeper exposure (more faint bits show up.) That's a heavy win for the A7s, regardless of the small difference in image scale.

The A7s wins here primarily because of higher Q.E. It's 65% Q.E. for the A7s, 47% Q.E. for the 6D. That is a MASSIVE difference. It's the reason the A7s pulls ahead despite all the advantages for the 6D. The A7s, despite a very similar photon flux per pixel, is converting more of those photons to charge. That's how it's able to build up a stronger signal in less time, and with less total integration. It's mainly converting more photons to charge in each pixel. On the other end of the spectrum, the A7s extremely low dark current noise (about an order of magnitude lower than the 6D), and similar read noise to the 6D. The lower dark current results in deeper background exposure, which picks up some more faint stars and renders a cleaner background.

Some of these technological differences don't mean as much for daytime photography. Certainly the noise characteristics of the A7s make it an amazing camera for low light photography...the low read noise and dark current and large pixel capacities result in image signals at ultra high ISO settings that are nearly devoid of electronic noise (read noise is sub-electron, dark current is so low that for most high ISO images you wouldn't even get 1ADU...so effectively zero dark current noise). These technological differences are quite huge when it comes to astrophotography, however. All the low noise and high sensitivity means very good signals with shorter exposures and less total integration time than other cameras.

The only real drawback with the A7s is the lossy compression in the RAW images. That can sometimes result in artifacts. However it does not seem to actually result in artifacts very often, and real-world results are usually exceptional. Hopefully at some point soon here Sony will "fix" their RAW issue with a firmware update, and lossy compression will no longer be a problem. Then there is essentially nothing negative I could say about the A7s as an astro camera.

 

[psolberg]

I'm still hoping they will not bump the MP on the S. My preference would be an 8K readout that scales to 4K just as they are doing with the 5k? readout that scales to 4K on the A7RII. No line skipping pixel binning or whatever crap caused the soft 5DmkIII video. I doubt this will be a full sensor readout, but hey, this is sony. They are the leader in this stuff so why not dream?

Even if they have to crop to APS-C, I would prefer that to the super 35 crop of the RII model just to achieve that shallow DOF look easier without the excessive crop.

 

[benperrin]

Thanks Jrista for your response by the way. Sorry it took me a while to reply. I think I'm going to cancel my 5dsr pre-order as I have no idea when it's going to arrive (company won't even give me an estimate). I'm going to purchase the a7rII and the commlite adaptor and I'll probably be using manual focus most of the time. Then later on I'll either purchase a 5dsr or 5d4 depending on what comes up. If the sony ends up being terrible I'll just return but at least this way I can find out if it is right for me. I see this more as adding a camera to my Canon kit rather than ditching Canon for Sony. Thanks for everything you write on this forum even if some of it goes over my head.

 

[benperrin]

By the way for anyone interested some a7rII high iso shots have been posted. Pity the photographer didn't know how to focus the thing.
http://www.cameraegg.org/sony-a7rii-new-100-crop-sample-image-at-iso-25600-and-full-size-raw-image-at-iso-6400-w-fe-pz-28-135mm-f4-g-oss/
http://www.cameraegg.org/first-high-iso-12800-25600-sample-images-of-sony-a7rii

Hard to tell everything when the full size jpg/raw files weren't provided for some but it does give an overall estimation. These are the same pics that 3kramd5 was able to find it's just that now 100% crops have been added.

 

[3kramd5]

By the way for anyone interested some a7rII high iso shots have been posted. Pity the photographer didn't know how to focus the thing.
http://www.cameraegg.org/sony-a7rii-new-100-crop-sample-image-at-iso-25600-and-full-size-raw-image-at-iso-6400-w-fe-pz-28-135mm-f4-g-oss/
http://www.cameraegg.org/first-high-iso-12800-25600-sample-images-of-sony-a7rii

Hard to tell everything when the full size jpg/raw files weren't provided for some but it does give an overall estimation. These are the same pics that 3kramd5 was able to find it's just that now 100% crops have been added.

Not bad for 1600. I'd call that more than usable.

 

[benperrin]

I'm thinking up to iso 12800 is usable from the a7rII. Wouldn't want to use it all the time but in a pinch it would be acceptable I think.

 

[3kramd5]

I'm thinking up to iso 12800 is usable from the a7rII. Wouldn't want to use it all the time but in a pinch it would be acceptable I think.

I'll wait for mine to deliver to make that call. The 12.8k photo is questionable, but I can't decide whether it's the camera's fault or the operator's.