The digital zoom on the a7s is almost lossless

Interesting. I wonder if the rx10 is the same too because that also does a full sensor readout. Do you have the fz1000? How is the autofocus in video? Does it hunt?
 
Thanks for the link and making the video.

This is what I hoped would be the case and what I expected. But you are the first person to post a proper test to show it.

One thing I found interesting is that if you click between 4.20 and 4.43 you can see that 2* zoom in full frame is about equal to 1.3* zoom in apsc mode. But strangely the latter looks more detailed.

Have you tested aliasing and moire at all with these zoom modes?

It would be interesting to try and get a 1 to 1 crop of the sensor with the zoom to see if there was a jump in detail and moire resistance.
knowing that the horizontal resolution of a7s = 4240 you can work out that
a 1 to 1 pixel crop of 1920*1080 resolution is a 2.20833 crop of full frame. So the digital zoom in full frame mode doesn't quite make it.

Despite sony apsc being colloquially referred to as 1.5 crop it is actually 1.5254 crop, which is why 1* zoom on apsc is slightly more magnified that 1.5 zoom in full frame mode.
apsc mode should use around horizontal 2779.5 pixels. so probably 2780.
so a 1 to 1 crop at 1920*1080 resolution is a 1.4479 crop of apsc.

Can the zoom only go up in tenths or can you tune it finer? I guess not that fine.
 
you can go in between the tenths. like if you use the left and right buttons as opposed to the wheel you can get in between the 10ths.

One thing I found interesting is that if you click between 4.20 and 4.43 you can see that 2* zoom in full frame is about equal to 1.3* zoom in apsc mode. But strangely the latter looks more detailed
Click to expand...

I noticed that too. my guess is that the processor is doing a better job of scaling down the apsc crop to 1.3x than the full readout to 2x.

It would be interesting to try and get a 1 to 1 crop of the sensor with the zoom to see if there was a jump in detail and moire resistance.
knowing that the horizontal resolution of a7s = 4240 you can work out that
a 1 to 1 pixel crop of 1920*1080 resolution is a 2.20833 crop of full frame. So the digital zoom in full frame mode doesn't quite make it.
Click to expand...

I actually did do that (didn't put it in the video though) comparing a jpeg at 1 to 1 with the digital zoom zoomed in to about where it would be one to one. the jpeg at one to one has noticeably more detail.

Have you tested aliasing and moire at all with these zoom modes?
Click to expand...

not specifically, but i did use that particular painting because on a lot of other cameras i used it's kind of a moire machine (especially on the 5n and t2i.) I did an outdoor test that didn't make it into the video with a roof that would cause aliasing on lesser cameras and i didn't see any. i don't know if you have the a7s or not but it really doesn't have any aliasing or moire issues (except in the faster framerates)

my guess is that Sony didn't put a great deal of engineering muscle behind making this mode all it could be (if they did they probably would be advertising it) but I think the fact that digital zoom is useful at all is just a happy consequence of the full sensor readout.

anyway, thanks for watching the video! appreciate it.
 
Does this basically mean I can put my a7s clip on premiere time line click effects > scale > and start ramping up the size to maybe 150 and still get a pretty decent sharp image?
 
isck29 said:
Does this basically mean I can put my a7s clip on premiere time line click effects > scale > and start ramping up the size to maybe 150 and still get a pretty decent sharp image?
Click to expand...
no because that's a post-process, what's being talked about here is what happens between the sensor and the camera's cpu, anything you do in editing will result in loss, but many people use 10-20% scaling/zooming in post pretty happily, so long as it's not out of focus/not overly noisy/etc...
 
Makes the compression appear larger but man, this is a good trick to have in the bag. Awesome find!
 
TerryKim3x8 said:
my guess is that Sony didn't put a great deal of engineering muscle behind making this mode all it could be (if they did they probably would be advertising it)
Click to expand...

I think you might be correct.

My current understanding is that when shooting video, the sensor always operates in 4k and downscales to 1080p -- except when the camera is set to 1080p60 or 720p100/120. Thus the degraded image quality at those two profiles.

You would think that with the full 4k readout of the sensor, it would have been possible to crop to 1:1 1080p (4x zoom) without any interpolation.
 
TerryKim3x8 said:
...didn't put a great deal of engineering muscle behind making this mode all it could be (if they did they probably would be advertising it) ...
Click to expand...


But, Sony is advertising it. It's called "clear image zoom." It's been on their cameras at least since the NEX-5T (but I know my NEX-5N does not have it). The Canon EOS 70D is also able to crop the sensor like this (they call it, "movie digital zoom"). I think the GH4 can as well?

Best,
Andrew
 
Good find. I had not noticed that.

Too bad it's not a bit smoother -- as it only moves in 1/10s.

I seem to recall reading a post by someone who said they were able to get the ClearZoom to move in less than 1/10 increments -- but I could not duplicate their results -- nor could I find Sony documentation supporting that feature.

However, that would be a nice adjunct to being able to use the Remote Control.

If anyone knows that setting -- please share.
 
I played around with the Sony FE 24-70mm (digital zoom times 4) and compared it to the Sony Powerzoom 18-200mm (APS-C mode). I am sorry, but "almost losless" is an exaggeration, at least in the infinity area.
The closer you are, the better the sharpness seems to be. Infinity with maximal tele lense you can see on the stills.Powerzoom 18-200mm 12800 ISO.jpgFE 24-70mm x4 Digitalzoom 3200 ISO.jpgPowerzoom 18-200mm.jpgFE 24-70mm x4 Digitalzoom.jpg
 
blafarm said:
Good find. I had not noticed that.

Too bad it's not a bit smoother -- as it only moves in 1/10s.

I seem to recall reading a post by someone who said they were able to get the ClearZoom to move in less than 1/10 increments -- but I could not duplicate their results -- nor could I find Sony documentation supporting that feature.

However, that would be a nice adjunct to being able to use the Remote Control.

If anyone knows that setting -- please share.
Click to expand...

I have the zoom function mapped to c2 so I can use it while filming. When using the arrow keys I can get sub 1/10 increments. Not really sure what the increments are since it only displays down to 1/10 but I can adjust zoom and see the change on the screen even though the zoom factor displayed isn't changing.
 
dhessel said:
I have the zoom function mapped to c2 so I can use it while filming. When using the arrow keys I can get sub 1/10 increments. Not really sure what the increments are since it only displays down to 1/10 but I can adjust zoom and see the change on the screen even though the zoom factor displayed isn't changing.
Click to expand...


I see what you are saying, and it appears to not be related to the zoom being mapped to C2 or any other button (or the Wired Remote for that matter).

What I am seeing is a maximum of two steps ONLY at one or more of the following settings 1.1, 1.2, 1.3.

In other words, whether using the on-camera buttons, or using the Wired Remote, I am able to get a single additional amount of zoom at one or more of the above numbers -- without the tenths indicator incrementing upwards.

The additional increment does not seem to be repeatable, in other words, it doesn't always happen on the exact same tenth number -- and repeated testing seems to indicate that it never happens at a tenth number above 1.3.

Are you seeing the same thing?
 
benn said:
I played around with the Sony FE 24-70mm (digital zoom times 4) and compared it to the Sony Powerzoom 18-200mm (APS-C mode). I am sorry, but "almost losless" is an exaggeration, at least in the infinity area.
Click to expand...

I'm not the OP, so I never made any claim to almost lossless.

However, the fact that you're seeing 4x zoom seems to indicate that you are not set to "ClearImage Zoom" -- which is fundamentally limited to 2x zoom.

I will admit that even with ClearImage Zoom, a 2x enlargement includes some level of image degradation -- especially at the long end of the lens.
 
benn said:
I played around with the Sony FE 24-70mm (digital zoom times 4) and compared it to the Sony Powerzoom 18-200mm (APS-C mode). I am sorry, but "almost losless" is an exaggeration, at least in the infinity area.
The closer you are, the better the sharpness seems to be. Infinity with maximal tele lense you can see on the stills.
Click to expand...

Yes. I think the zoom should be "lossless" up to about a 1.5 crop from apsc mode (same but sharper than a 2* crop from full frame mode), which is using round about a 1920*1080 crop of the sensor. Any more than this and you are up-scaling instead of downscaling, so you're not getting more detail, you are just enlarging the detail you already have.

To take it to the extreme, no-one would ever expect a 70mm lens with a 100 times digital zoom using about a 1 thousandth of a megapixel portion of the sensor to match a 7300mm lens using the full sensor, for example.
 
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