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In praise of in-camera Digital Zoom


kye
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I've recently "discovered" some of the benefits of using the in-camera digital zoom.  These won't apply to everyone, but it's worth considering and I don't hear a anyone talking about it.

Let me illustrate by taking my GH5 as an example, but the principle applies much wider, especially as cameras go towards 8K and beyond.

The GH5 has a sensor that's 5184 pixels wide.  When you're shooting 4K, the camera downsamples the 5.2K to 4K, giving a higher quality image due to the benefits of oversampling.  The benefits of oversampling are well known, and many cameras have this.

The GH5 also has an ETC mode, which essentially does a 1:1 crop into the middle of the sensor.  This is a common feature across manufacturers.
If you use the ETC function in 4K, you get an additional 1.3x crop, and if you use the function in 1080p then you get a 2.7x crop.  
Both of these modes are shooting a 1:1, so you get a tighter FOV, but the image is no longer oversampled, so the quality goes down.

Enter the digital zoom.

In 1080p mode, the GH5 allows a 2x and 4x digital zoom.  The 2x digital zoom is less than the 2.7x 1:1 zoom from the ETC mode, so (assuming that the cameras image pipeline is designed well) the resulting 1080p image should be an image that is taken from the middle 2.6K pixels and downsampled to 1080p.

In other words, the 2x digital zoom is a way to punch-into the sensor but still keep the quality of an oversampled image.

This principle will occur any time that the digital crop is less than the crop of going to a 1:1 area on the sensor for whatever resolution you're shooting in.

The Sony ClearImage Zoom comes to mind here, where (I think?) you can zoom in by a lesser amount than the 4K 1:1 crop (which is something like 1.5x?).  Perhaps other manufacturers have similar functionality too.

Of course, the lower the resolution you're shooting then the more likely this will be available on your camera.  For those still shooting 1080p then this is worth looking at.

For those shooting 4K, this will increasingly be useful as sensors creep up towards 8K and beyond.

For me though, I've now abandoned the idea of having to buy an 85mm prime, because I can simply do a 2x digital zoom with my 42.5mm lens and get the same FOV and (basically) the same image quality, and if I happen to have my 7.5mm lens on and want to quickly grab a 15mm FOV shot then I know I won't be sacrificing quality to get one.

Had I known that this feature delivered such good results I may have actually bought different lenses, so it's not a trivial thing, and it's worth giving a quick go if your camera supports it.

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My project for today actually with my new S5.

I have been shooting video in cropped APSC format for years so continuing to do so on this FF body is ‘normal’ to me and something I like because I generally prefer a tighter crop and the medium wide zooms and primes have been perfect in that regard.

But for stills, I sometimes need a bit longer reach but at the same time would rather not use zooms and would prefer not to switch lenses.

Enter shooting FF but with the ability to switch to a crop such as making an 85mm become like a 125/130mm at times.

Never had a FF camera before so testing this today...

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I love Sony clearzoom.

The thing is it is VARIABLE so even a very fast prime becomes a 2x zoom with little loss of image quality.

Most recent (if not all) Sony digital cameras have both clear image zoom and digital zoom (clearzoom is to 2x, digital zoom is to 4x).

I do not know what (or if) there is a difference between clearzoom and digital zoom at and below 2x.

Sony cameras give the option of optical only, clear image zoom or digital zoom.

I usually have my A7s set to be able to use clear image but my RX100iv most of the time is set to optical only.

Towards 2x clearzoom CAN have that digital zoom look sometimes but it also comes in handy for using smaller format lenses that do not cover FF.

I have the A7s set so I can use it on the fly and including for video.      Looking for a better remote control that will let me use it (my current cheap remote is not great using it).

I did not mind ETC on the GX7 but it was not something I used often.

I think the A7siii does not allow clearzoom in 4k video??  Did I see that?

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Whether using an oversampled crop or a straight crop via digital zoom, compared to using a longer lens, you still zoom in on (i.e. enlarge) two things you may not want: 1. Noise, and 2. any discernable softness in your glass. A longer lens (of equal sharpness and optical quality in all respects etc) gets you your tighter FOV without intensifying noise or softness. But yeah, on the GH5 that's a more clever method than what I used to do (just had Ex Tele Conv set to a Fn button), I hadn't thought about this.

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Having something that was continuous would be great, like the Sony one, and the JVC and FS5 ones.

It's not that difficult a thing to implement technically, so it's cool that some manufacturers did it.

The thing to watch is that when your digital zoom is more than a 1:1 crop you're actually upscaling in-camera, and the quality falls off a cliff at that point.
I tried 2x, which is a 1.35x downsampled image, but the 4x is 1.5x upsample so it's taking about 1.3K and upscaling it to a 2K image, which does not look good!

Really, the proof is in the resulting image, so just give it a go and see how your camera performs.

2 minutes ago, dgvro said:

Whether using an oversampled crop or a straight crop via digital zoom, compared to using a longer lens, you still zoom in on (i.e. enlarge) two things you may not want: 1. Noise, and 2. any discernable softness in your glass. A longer lens (of equal sharpness and optical quality in all respects etc) gets you your tighter FOV without intensifying noise or softness. But yeah, on the GH5 that's a more clever method than what I used to do (just had Ex Tele Conv set to a Fn button), I hadn't thought about this.

Absolutely, you're zooming into the noise and the softness of your glass.  

Given that most lenses soften up when stopped down a bit from their widest aperture, you may find that a general rule-of-thumb might be to stop down a bit when using the zoom function.

When you're keeping the digital zoom in the range where it's still downsampling then you do get the NR benefits of rescaling.  We saw that the benefits of a 5.2K image downscale to 4K was a decent improvement on things like noise, and that's only a 1.35x downscale (on the GH5) so it doesn't take a huge amount to smooth out the noise, assuming that the noise is pixel-sized, rather than the Canon noise that spans multiple-pixels for some unknown reason.

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A drone that really punched above its weight in its time, the Anafi from Parrot, had a 'lossless' continuous digital zoom like this when shooting at less than 4k. Set to a shoulder trigger on the controller. I don't know if there was any oversampling involved even when not zoomed on that thing (I think it had a 20MP sensor) but yeah the zoomed stuff didn't generally look worse than the non-zoom 1080 from what I remember. Great drone vs the DJI equivalents of that gen. Signal transmission just let it down a bit.

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Well if it exists for the Panny S5, I can't work out how. 

Stills I'm there now, though not having the crop in raw means I'll probably just buy the longer lens.

Might be useful for video, but then pretty happy with the standard focal lengths with the lens I have.

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For anyone wanting a bit more tactile control of the clear image zoom on Sony cameras, this Fotga RM-VS1 will give you a zoom rocker to operate it with as well as a shutter release, record button and power on/off.

679160403_ScreenShot2020-09-24at16_30_49.png.0c25ec8be8f3418bbc8bc0aca6f3bde3.png

If you are using a lens with servo zoom such as the PZ18-105mm f4 etc then it controls both the optical zoom and the clear image zoom as one (kind of continuous) lens. I say kind of because there is a slight pause when zooming in when it gets to the crossover point at the end of the optical range.

If you've got an RX100 then it also controls the optical and clear zoom extension in the same way.

There is no variable speed so don't expect to be doing variable speed zooms but its good for framing if nothing else.

Expect to pay around €16-18 on Ali or €20-25 on Amazon.

 

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