aclo
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Contributing Member
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Posts: 554

Re: A picture is worth a 1000 words

JimKasson wrote:

aclo wrote:

JimKasson wrote:

aclo wrote:

Even if this was an exact relation, it relates the system resolution to those of the lens and the sensor. And it's consistent with saying the lens can outresolve the sensor: if the lens resolution is rL, the sensor resolution is rS and the total system resolution is rT then we have 1/rT=1/rL+1/rS. If say rS is much larger than the rL, so the sensor outresolves the lens, ie rS>>rL, then 1/rS<<1/rL so 1/rT=1/rS+1/rL is approximately equal to 1/rL or in other words rT=rL, ie, the lens resolution limits the total resolution (or, increasing the sensor resolution won't increase the system resolution). I'm not sure how this equation implies a lens can't outresolve a sensor, the equation itself tells you that if one of the rL or rS is much larger than the other then the lower one determines the overall resolution.

Define “resolution” as you’re using it above, please. But the above ignores the sampling frequency, doesn’t it? And the sampling frequency is key to knowing whether the sensor is out resolved by the lens.

I can't, as I don't know where the relation came from and am not defending the equation. I am saying that the qualitative picture that equation gives is that if the "resolution" of one of (lens, sensor) is much smaller than the other then that limits the total "resolution," no matter how much you increase the other. So I am unsure why it would be at odds with saying one of the two components can "outresolve" the other, as I interpret "outresolve" as "have much more resolution which then becomes useless as it does not contribute any more to the system resolution".

But I’m talking about something else entirely, and that’s aliasing. That’s a clear indication that the lens is out resolving the sensor, because the system mtf at the Nyquist frequency is too high.

I appreciate that if you have detail in the image at high enough freqs it aliases down and in this instance causes visual artifacts in the frequencies reproduce. So that is a real sense in which you "outresolve" the sensor. I was simply pointing out that the equation itself supports the notion that either of (lens, sensor) can have too much resolution which contributes nothing to the result.

However I now realise that possibly the earlier rhetorical question as to whether the equation needs updating meant that the eqn says that too much lens resolution does nothing, rather than actually worsen things (which I think is what you are focussing on, correct? or am I still missing the point here?)