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Oscilloscope Zoom Out Quirk
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SilverSolder:

--- Quote from: Wuerstchenhund on May 11, 2020, 11:11:17 am ---
--- Quote from: SilverSolder on May 11, 2020, 01:57:48 am ---Imagine a camera with a zoom lens.  An experienced photographer does not start with the lens zoomed out to the max, and then only zooms in from that point.  Instead, they start with the lens zoomed somewhere around where their experience tell them is the best zoom factor for the kind of picture they are taking, then they trim the zoom both in and out a little bit from that point while watching the model in the viewfinder, until he/she looks "just right".  It is a fast and fluid way of working with a camera.
--- End quote ---

Very bad analogy. Because optical zoom on a camera changes the resolution per scene area, so capturing pictures fully zoomed out will result in a loss of information when creating closer-ups from that 'acquisition'.

On deep memory scope however, capturing long and zooming in does not result in a loss of information, because neither the vertical resolution nor the sample rate changes over capturing short.

I can tell you that, if the loss of information (detail) wasn't a problem with zoom then many photographers would gladly capture fully zoomed out, because by capturing excess scenery they can later easily adjust the actual image size and position without having to go back to the place of scene and re-capture.

--- End quote ---

If you have enough RAM in the scope, of course I agree.   But if you capture a "zoomed out" picture of a waveform on your scope of say, 10 seconds, just to pick an extreme,  and your scope does not have enough RAM to capture that at full resolution, there is indeed a loss of quality compared to capturing a smaller time slice at a higher rate.   That's my situation...


SilverSolder:

--- Quote from: 2N3055 on May 11, 2020, 11:52:16 am ---
--- Quote from: SilverSolder on May 11, 2020, 11:42:52 am ---
--- Quote from: nfmax on May 11, 2020, 07:46:09 am ---[...] However, instead of using 'spare' memory for off screen capture, I rather like the Siglent technique of keeping a history of previous acquisitions you can go back and look at [...]

--- End quote ---

Is that what "save to disk" or "save to usb" etc does?

--- End quote ---

No, scope memory is used in seamless segmented mode, meaning scope keeps hundreds of previous "screens" (trigger events) at all times, transparently. With no performance impact to normal use.

--- End quote ---

So you can scroll back and view previous events? -  That does sound kind of cool. 
2N3055:

--- Quote from: SilverSolder on May 11, 2020, 11:53:20 am ---
--- Quote from: Wuerstchenhund on May 11, 2020, 11:11:17 am ---
--- Quote from: SilverSolder on May 11, 2020, 01:57:48 am ---Imagine a camera with a zoom lens.  An experienced photographer does not start with the lens zoomed out to the max, and then only zooms in from that point.  Instead, they start with the lens zoomed somewhere around where their experience tell them is the best zoom factor for the kind of picture they are taking, then they trim the zoom both in and out a little bit from that point while watching the model in the viewfinder, until he/she looks "just right".  It is a fast and fluid way of working with a camera.
--- End quote ---

Very bad analogy. Because optical zoom on a camera changes the resolution per scene area, so capturing pictures fully zoomed out will result in a loss of information when creating closer-ups from that 'acquisition'.

On deep memory scope however, capturing long and zooming in does not result in a loss of information, because neither the vertical resolution nor the sample rate changes over capturing short.

I can tell you that, if the loss of information (detail) wasn't a problem with zoom then many photographers would gladly capture fully zoomed out, because by capturing excess scenery they can later easily adjust the actual image size and position without having to go back to the place of scene and re-capture.

--- End quote ---

If you have enough RAM in the scope, of course I agree.   But if you capture a "zoomed out" picture of a waveform on your scope of say, 10 seconds, just to pick an extreme,  and your scope does not have enough RAM to capture that at full resolution, there is indeed a loss of quality compared to capturing a smaller time slice at a higher rate.   That's my situation...

--- End quote ---
If you have short memory scope there won't be any data "outside the screen" either..
SilverSolder:

--- Quote from: Wuerstchenhund on May 11, 2020, 11:29:03 am ---
--- Quote from: tv84 on May 10, 2020, 05:19:40 pm ---Gentlemen, you are ALL talking the same language!

Nico starts with zoom in and likes to be able to zoom out. The others start with zoom out and like to be able to zoom in.

It's all the same, but in reverse order.

All the rest are just details (and personal preferences or lifelong habits)!

--- End quote ---

Unfortunately, it's not the same.

"Zooming in" as in the standard method is done (you guessed it!) through the scope's zoom function. It provides references as for the position on the captured signal, can be displayed together with the full signal and works for single and continuous acquisitions.

As to "zooming out", most scopes don't allow zooming outside the scope area.

However, some scopes allow post-acquisition change of the timebase.

Nico's method uses this as a means to "zoom out". However, it's not really a zoom, it's a change of timebase post-acq. And because it's a change of timebase post-acq, it *only* works if the scope is halted (i.e. no new triggers) and you can't display it together with the "zoomed in" view (well, you could probably use waveform memory, but you'd lprobably ose the timing information).

So while the end result of both methods are the same in the cases where Nico's method works, they are *not* achieved the same way.

--- End quote ---


There is only so much real estate on the screen.  If you already have 2 analog channels plus a handful of digital ones, using the zoom window becomes a bit of a pain (uses too much space) compared to just altering the timebase "post facto".   Those multi-channel captures are also the kinds of scenarios where you most often end up looking for things that happened "off screen", in my experience at least.
2N3055:

--- Quote from: SilverSolder on May 11, 2020, 11:58:12 am ---
--- Quote from: 2N3055 on May 11, 2020, 11:52:16 am ---
--- Quote from: SilverSolder on May 11, 2020, 11:42:52 am ---
--- Quote from: nfmax on May 11, 2020, 07:46:09 am ---[...] However, instead of using 'spare' memory for off screen capture, I rather like the Siglent technique of keeping a history of previous acquisitions you can go back and look at [...]

--- End quote ---

Is that what "save to disk" or "save to usb" etc does?

--- End quote ---

No, scope memory is used in seamless segmented mode, meaning scope keeps hundreds of previous "screens" (trigger events) at all times, transparently. With no performance impact to normal use.

--- End quote ---

So you can scroll back and view previous events? -  That does sound kind of cool.

--- End quote ---
Not only scroll. Search, measure, make histograms, create display persistence (overlap them all), decode protocols...etc...
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