Hi Chuck, Ken, C.H., Moose and all,
> From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
> Only at
> f/5.6 to f/11 is the 70-200 able to equal or slightly exceed the 12.7
> megapixels of the 5D sensor (represented by the line labeled "Nyquist
> frequency"). Below f/5.6 some irregular things start happening and
> above f/11 diffraction begins its steady toll against resolution.
>
Yes, but this is a "photographic resolution" measure; that is, the resulting
lens+sensor (or film) combo, so it's not fully representative of lens'
performance alone.
That said,
> it's also easier to make a lens that resolves little pixels if the
> sensor is small and the lens doesn't have to cover a large area.
>
I agree.
From: Ken Norton <ken@xxxxxxxxxxx>
> Well, I disagree in one aspect. It takes a minimum of twice the sensor
> resolution to maximize lens resolution--and that's when the res chart is
> perfectly aligned with the sensor. What about diagonal details? Sorry, you
> need much more sensor resolution than what the lens is capable of
> producing.
I'm with Ken on this. Film will reach its resolving power no matter where or
which orientation, but digital's grid sampling may need way more than two
pixels in order to resolve a line-pair. And if we have into account Bayer's
issues...
> but just maybe I need to focus
> less on technical aspects and more on artistic aspects.
>
And so I need ;-)
From: "C.H.Ling" <ch_photo@xxxxxxxxxxxxx>
> I remember people mentioned the 'aerial resolution' (?) of lenses can over
> 200lp/mm.
Yes, "aerial" resolution, agains "photographic" resolution, is the resolving
power of the lens alone, without the limitations of the film or sensor.
I have a strong feeling that my 24/2 can do
better with higher than 21MP sensor.
>
I'm pretty sure too, the 24/2 is an excellent performer. Do anyone out there
want to part with one of them? ;-) ;-) ;-)
From: Moose <olymoose@xxxxxxxxx>
> 1. Judgments/measurements are made with a camera with AA filter in
place.
Interesting point.
2. The lppmm standard, while a good method to compare cameras with
> different sensor sizes, is not ideal for lens comparisons or judgments
> about lens vs. sensor resolution.
>
Not sure about what you mean... but I think it's inside the human behaviour
the desire to get a simple number to measure things, to be able to say "mine
is bigger than yours!" :-) :-) :-)
3. A nit pick. How can the system out resolve the "theoretical
> resolution of the sensor", Nyquist frequency?
>
The Bayer matrix is, indeed, a very strange thing, and I feel demosaicing
algorithms as rather obscure... so not sure which would be the _real_
Nyquist frequency of a Bayer sensor -- but see my point about Ken's quote.
1. Back in the area of #1 above, system bandwidth is a complex function
> of the bandwidths of the components.
Or not so complex?
Even the
> formula someone posted a little bit ago is probably too simple in the
> real world.
Don't recall the post, but [where the hell is my 'Optical Instrumentation'
book??? Oh, it's here, below the Bessa R3A ;-)] it's usually defined as:
"The inverse of the resolving power of the system, is equal to the sum of
the inverses of the resolution of the individual components"
But just like frequency response in audio, resolution should be measured at
certain conditions, and should be the same in all components.
Increase the resolving power of any one component and system resolution goes
> up. If the improved component was the poorest, it goes up a lot,
> but not as much as the % increase in the component. If it was already
> the broadest component, bandwidth increases only a little. But it does
> change.
I agree. So there _is_ a reason for higher MP's ;-)
2. These luminance only, test pattern tests don't say a thing about
> spatial color resolution. If Foveon sensors had fulfilled their apparent
> potential, this wouldn't be an issue.
>
Very intersting point. I was very interested in Foveon sensors -- seems to
me as the way to go. But I'm afraid that the technically worst solution is
the one to succeed -- as usual :-(
3. There is an unspoken assumption in most web discussions of color
> accuracy in digicams, but it is wrong. When we talk about sensors, we
> act like the array filters are at least close to perfect. It just ain't
> so. Look at the spectral responses of even the best quality photographic
> filters. They aren't sharp cut-off tools, not even close.
There's no real need for it, as the spectral response of the cones isn't
either. But they should mimic the spectral response of the eye, and the tiny
filters in microlenses seem to be far from it.
> 4. No matter what the resolution chart tests say, all digital capture
> involves sampling and that sampling always reduces
> sharpness/contrast/clarity/whatever along any edge that is not exactly
> aligned with the sensor array.
Agreed -- even more with the Bayer trick.
That they don't say it all is
> testified to by the decades of testimony of practical photographers
> about meaningful difference between lenses that aren't reflected in
> simple resolution tests.
Sure, that's why I prefer a more "real world" test.
Cheers,
--
Carlos J. Santisteban Salinas
IES Turaniana (Roquetas de Mar, Almeria)
<http://cjss.sytes.net/>
--
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