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Sensor resolution, any sites with actual measurements?

 
 
Helen
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      03-05-2006

"Alfred Molon" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ...
>> Still spelling its with an apostrophe I see.
>>
>> And it's 'affect', not 'effect'.

>
> Maybe Rich is not a native English speaker.
> --
>

No excuse (but he is anyway).
He's been told how to spell 'its' before.



 
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Rich
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      03-05-2006
I think some of the higher-end Canon L-telephotos are nearly as sharp
wide open
as stopped down because of precise engineering and the use of the best
lens materials.

 
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Rich
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      03-05-2006
If this is the case, then why don't digicams with small sensors and
tiny pixels
resolve more than DSLRs?

 
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David J Taylor
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      03-05-2006
Rich wrote:
> If this is the case, then why don't digicams with small sensors and
> tiny pixels
> resolve more than DSLRs?


In lines per mm terms, they do.

David


 
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Neil Ellwood
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      03-05-2006
On Sun, 05 Mar 2006 19:30:28 +0000, David J Taylor wrote:

> Rich wrote:
>> If this is the case, then why don't digicams with small sensors and
>> tiny pixels
>> resolve more than DSLRs?

>
> In lines per mm terms, they do.
>
> David

But only on the sensor.
--
Neil
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Neil Ellwood
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      03-05-2006
On Sun, 05 Mar 2006 14:41:31 +0100, Alfred Molon wrote:

> In article <snq7dt1v8fhbggo9if3rmj9ks3@inews_id.stereo.hq.phi coh.net>,
> http://www.velocityreviews.com/forums/(E-Mail Removed) says...
>
>> 'Wide open' is a rather useless requirement.

>
> Well no, you might have to use the lens at the widest aperture because
> there is not sufficient light.
>
>> If you look at MTF graphs, wide angle lenses simply don't have great
>> corner sharpness. You want high-end telephoto lenses for that (or stop
>> down far enough).

>
> Why can't they design WA lenses with corner to corner sharpness (even
> wide open)?

Ask a lens designer - they will probably tell you that it is a combination
of physics, engineering tolerances and available glass specifications.

--
Neil
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Alfred Molon
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      03-05-2006
In article <h8EOf.11802$(E-Mail Removed)>,
(E-Mail Removed) says...
> Unless there is an uncommon amount of crosstalk, most CCD chips come
> close to their theoretical capability, which is about 0.7 of the line
> frequency of the detectors. That is, if there are 100 detectors per mm,
> then the chip will usually test out at about 70 lines (35 lp) per mm.
> While the mtf curve for a discrete sensor is shaped a bit different than
> for a scanning sensor (Kell factor), the curves are close near the
> cutoff frequency or the 2% contrast point.


Where do you get this 70%? If a pattern with n white lines and n black
lines falls exactly on the lines of the CCD, so that each CCD line sees
either a black line or a white line, the CCD will have a resolution of
100% of the nominal pixel count. Maximum MTF. On the other hand if each
CCD line sees half of a black line and half of a white line, the CCD
will see a uniform gray (zero MTF).
--

Alfred Molon
------------------------------
Olympus 50X0, 7070, 8080, E300, E330 and E500 forum at
http://groups.yahoo.com/group/MyOlympus/
Olympus E500 resource - http://myolympus.org/E500/
 
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Don Stauffer
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      03-06-2006
Neil Ellwood wrote:
> On Sun, 05 Mar 2006 19:30:28 +0000, David J Taylor wrote:
>
>
>>Rich wrote:
>>
>>>If this is the case, then why don't digicams with small sensors and
>>>tiny pixels
>>>resolve more than DSLRs?

>>
>>In lines per mm terms, they do.
>>
>>David

>
> But only on the sensor.

But I thought that was what the question was about, resolution of the
SENSOR.
 
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Don Stauffer
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      03-06-2006
Neil Ellwood wrote:

>>
>>Why can't they design WA lenses with corner to corner sharpness (even
>>wide open)?

>
> Ask a lens designer - they will probably tell you that it is a combination
> of physics, engineering tolerances and available glass specifications.
>

As a one time lens designer, I'll take a poke at this. It is the physics
and glasses, not tolerances.

In many cases lens design is a situation of solving a set of equations
with more variables than the number of equations- not enough degrees of
freedom. Each and every field angle is a new design parameter. What
provides proper correction at one field angle doesn't work at another
field angle. Each field angle differing from the previous case by the
desired resolution of the system is really a new case. The wider the
total field of view, the greater the number of variables (field angle in
this case), so the harder the job.

One of the nasty things that happens is that near the edge of the field,
the incidence angle on some surfaces gets very high. Surface reflection
goes up as incidence angle goes up and one starts getting a lot of flare
and ghost images, yet the greater the field angle, the harder it is to
design baffling.

Lens coatings only work well over a narrow range of angles.
 
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Don Stauffer
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      03-06-2006
Alfred Molon wrote:
> In article <h8EOf.11802$(E-Mail Removed)>,
> (E-Mail Removed) says...
>
>>Unless there is an uncommon amount of crosstalk, most CCD chips come
>>close to their theoretical capability, which is about 0.7 of the line
>>frequency of the detectors. That is, if there are 100 detectors per mm,
>>then the chip will usually test out at about 70 lines (35 lp) per mm.
>>While the mtf curve for a discrete sensor is shaped a bit different than
>>for a scanning sensor (Kell factor), the curves are close near the
>>cutoff frequency or the 2% contrast point.

>
>
> Where do you get this 70%? If a pattern with n white lines and n black
> lines falls exactly on the lines of the CCD, so that each CCD line sees
> either a black line or a white line, the CCD will have a resolution of
> 100% of the nominal pixel count. Maximum MTF. On the other hand if each
> CCD line sees half of a black line and half of a white line, the CCD
> will see a uniform gray (zero MTF).


Ah, but in a real resolution test there is NO guarantee that the lines
in the object chart will fall exactly on the line! That is exactly the
point. The kell factor and the 70% represent the PROBABILITY that the
lines and detectors line up exactly.

In real world imaging there is no way to ensure that exact line up in
phase, or that the bar chart will be aligned exactly in angle to be
parallel with rows or columns.
 
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