Sorry for bad wording regarding aliasing and "imaging". I do realize the difference between sampling signals above Nyquist that folds down below Nyquist (aka aliasing) and sampling signals below Nyquist but trying to reproduce them without a lowpass reconstruction filter (aka "brickwall-filter") which will casue imaging signals above Nyquist that was not there in the input.
I also realize that a sharp lowpass would give worse display of transient signals.
I guess I was expecting the sin(x)/x interpolation mode to use a brickwall lowpass filter similar to what you would find in an audio converter. Also an analog scope will be able to display a steady sine at the -3dB point in contrast to what we see in this case.
I understand now that for measuring sine waves properly between 2-5MHz you must use the FFT in Picoscope.
Using the math function in scope mode would work as well but I'm not sure how freely you can set filter characteristics.
Using SDK or exporting data to Excel or Matlab would be other options.
I don't necessarily need to have more than 1MHz "proper" bandwith in this scope but was pussled by what was going on. A friend of mine that recently started to use Pico products noticed the same thing and was surprised.
I also see that you have started to use more "oversampling" in the latest products. Having a bandwith spec significantly below Fs/2.
Having audio gear and analog scopes as a reference I guess it's easy to be confused by this.. althoug in hindsight it seems obvious.