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Resolution question

 
 
MikeM
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      07-04-2006
I'm new to digital and don't know much about them. I have an Olympus
C-7070 and have been taking close-ups of plant structures like growing
points and have noticed that when I view the images at 100 % there
have been very small insects that the 7.1 MP of my camera are not
quite enough to get good detail of. I use macro a lot so I was
thinking of trying to get a camera with more pixels. If I understand
correctly, the more pixels on a sensor of a given size, the more noise
becomes a problem. I have read that just going for the highest number
of MPs I can afford is not the best way to decide on a camera so I
would like to know if there are any cameras/brands that are better at
increasing the MPs while controlling the noise.

Thanks
Mike
 
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Steve Wolfe
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      07-05-2006
> I'm new to digital and don't know much about them. I have an Olympus
> C-7070 and have been taking close-ups of plant structures like growing
> points and have noticed that when I view the images at 100 % there
> have been very small insects that the 7.1 MP of my camera are not
> quite enough to get good detail of. I use macro a lot so I was
> thinking of trying to get a camera with more pixels. If I understand
> correctly, the more pixels on a sensor of a given size, the more noise
> becomes a problem. I have read that just going for the highest number
> of MPs I can afford is not the best way to decide on a camera so I
> would like to know if there are any cameras/brands that are better at
> increasing the MPs while controlling the noise.


Most likely, the problem is not the number of pixels, at least not a lack
thereof, but a lack of lens resolution. You see, the smaller you make the
pixels on a sensor, the more resolution you need from your lens to take
advantage of them.

After getting into the math, it turns out that a C7070 has about 430
pixels/mm, so in order to take advantage of that, you'd need to provide
resolution from the lens of at least 220 line pairs/mm. That is an
astounding figure that you're just not going to achieve. Most lenses' MTF
graphs are only given up to 30 or 40 lp/mm.

This is the reason that since the inception of photography, to capture
more detail, the best choice has been a larger film size, and the same holds
true with digital. You don't need more pixels, you need a larger sensor,
giving you larger pixels.

Unfortunately, there aren't many choices to give you significantly larger
sensors without going to an SLR. And of course, with larger sensors, depth
of field becomes more of a problem, but you're up against the laws of
physics here.

steve


 
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David J. Littleboy
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      07-05-2006
"Steve Wolfe" <(E-Mail Removed)> wrote:
>
> After getting into the math, it turns out that a C7070 has about 430
> pixels/mm,


I was about to argue that your math was wrong, but when I checked, I found
that you were right. Ouch. That really is an insane number of pixels per mm.

> so in order to take advantage of that, you'd need to provide resolution
> from the lens of at least 220 line pairs/mm.


Ah, but here is something to argue with. Dcams only resolve to about 2/3 of
Nyquist, not all the way out to Nyquist, so you need _decent contrast_ at
150 lp/mm or so. (Check out the test chart images at dpreview.)

> That is an astounding figure that you're just not going to achieve. Most
> lenses' MTF graphs are only given up to 30 or 40 lp/mm.


And here's something else. It turns out that lens performance goes up as the
format goes down; i.e. it's easier to make a sharp lens for a tiny format
than for a larger format.

(The limit on lens performance is diffraction. Diffraction imposes a 50% MTF
term at approximately 800/(f number), so if you need 150 lp/mm at decent
contrast, you need to be at f/5.6 or wider, and the tiny dcams lenses often
act as though they are close to diffraction limited at f/5.6. They really
are seriously impressive.)

The bottom line is that the insanely tiny insanely high pixel count consumer
dcams actually work, within the laws of physics and optics, quite nicely. As
long as you don't mind restricted dynamic range at the lowest ISO and noise
at higher ISOs.

> This is the reason that since the inception of photography, to capture
> more detail, the best choice has been a larger film size, and the same
> holds true with digital. You don't need more pixels, you need a larger
> sensor, giving you larger pixels.


Well, you need both.

It turns out that since lenses scale up in resolution as you scale them down
in size, the improvements from larger formats in digital are much more
subtle than the improvements from smaller film. The tiny dcams actually do
fly at resolutions up to at least 5 or 6MP.

> Unfortunately, there aren't many choices to give you significantly larger
> sensors without going to an SLR. And of course, with larger sensors,
> depth of field becomes more of a problem, but you're up against the laws
> of physics here.


Actually, it turns out that _maximum_ DOF (the DOF at the point you don't
want to stop down any more because diffraction will degrade your image at
any smaller f stop) is exactly the same _whatever the size of the sensor_ as
long as you are comparing cameras with the same number of pixels.

People with more sense than money who own cameras like the 1Dsmk2 or 5D will
see a lower max DOF than users of 6 or 8MP smaller cameras, but only because
they have higher resolution requirements (in lines per picture height terms)
than the smaller sensor cameras.

David J. Littleboy
Tokyo, Japan


 
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Hebee Jeebes
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      07-05-2006
Besides what other have said keep in mind that most macro functions on
cameras allow you to get closer and focus closer at full wide angle rather
than fully zoomed in. On my FZ30 (Panasonic) with 12X zoom I can get closer
at 1X than I can at 12X. At 1X I can get with in a couple of inches at 12X I
have to like 6 feet away. So try (if you aren't already) doing macro at full
wide angle. Look in your users guide for information on how close you can
focus at full wide angle in macro mode.

R

"MikeM" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> I'm new to digital and don't know much about them. I have an Olympus
> C-7070 and have been taking close-ups of plant structures like growing
> points and have noticed that when I view the images at 100 % there
> have been very small insects that the 7.1 MP of my camera are not
> quite enough to get good detail of. I use macro a lot so I was
> thinking of trying to get a camera with more pixels. If I understand
> correctly, the more pixels on a sensor of a given size, the more noise
> becomes a problem. I have read that just going for the highest number
> of MPs I can afford is not the best way to decide on a camera so I
> would like to know if there are any cameras/brands that are better at
> increasing the MPs while controlling the noise.
>
> Thanks
> Mike



 
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MikeM
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      07-05-2006

My C-7070 gets to 1.2 ", but with no flash, and most of my subjects
avoid bright light and are in positions that make using a tripod a
problem, and waiting for the wind to stop completely can waste a lot
of time. I use the SM option when there is enough light to hand hold.

I would like to get back to SLRs. I also used my 300 mm lens a lot
before I went digital. If I do get a DSLR should I avoid 4/3 camera as
I've read that the sensor is smaller than in other DSLRs?

Mike


On Tue, 04 Jul 2006 23:52:09 GMT, MikeM <(E-Mail Removed)>
wrote:

>I'm new to digital and don't know much about them. I have an Olympus
>C-7070 and have been taking close-ups of plant structures like growing
>points and have noticed that when I view the images at 100 % there
>have been very small insects that the 7.1 MP of my camera are not
>quite enough to get good detail of. I use macro a lot so I was
>thinking of trying to get a camera with more pixels. If I understand
>correctly, the more pixels on a sensor of a given size, the more noise
>becomes a problem. I have read that just going for the highest number
>of MPs I can afford is not the best way to decide on a camera so I
>would like to know if there are any cameras/brands that are better at
>increasing the MPs while controlling the noise.
>
>Thanks
>Mike

 
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Steve Wolfe
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Posts: n/a
 
      07-05-2006
> Ah, but here is something to argue with. Dcams only resolve to about 2/3
> of Nyquist, not all the way out to Nyquist, so you need _decent contrast_
> at 150 lp/mm or so. (Check out the test chart images at dpreview.)
>
>> That is an astounding figure that you're just not going to achieve.
>> Most lenses' MTF graphs are only given up to 30 or 40 lp/mm.

>
> And here's something else. It turns out that lens performance goes up as
> the format goes down; i.e. it's easier to make a sharp lens for a tiny
> format than for a larger format.


Are you claiming that the lens in that camera is going to provide any
decent contrast at even 150 lp/mm (at less than f/5.6), or do they just
cover it up with excessive sharpening after the fact?

Macro pictures with a 1.6x body and an EF-S 60mm macro lens completely
blow away anything I've seen P&S cameras do. Of course, a good part of that
is the fact that it's a true macro lens, not a zoom lens with a supposed
"macro" mode, but since the P&S can't have the lens changed, that is a valid
point.

At f/5.6, the airy disc is 7.5 microns, with the pixels being just a
little larger than 2 microns, so the airy disc from a point would cover 3
full pixels. That doesn't sound like 50% MTF to me, but we're getting into
an area that I'm less familiar with.

steve


 
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David J. Littleboy
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      07-05-2006

"Steve Wolfe" <(E-Mail Removed)> wrote:
>> Ah, but here is something to argue with. Dcams only resolve to about 2/3
>> of Nyquist, not all the way out to Nyquist, so you need _decent contrast_
>> at 150 lp/mm or so. (Check out the test chart images at dpreview.)
>>
>>> That is an astounding figure that you're just not going to achieve.
>>> Most lenses' MTF graphs are only given up to 30 or 40 lp/mm.

>>
>> And here's something else. It turns out that lens performance goes up as
>> the format goes down; i.e. it's easier to make a sharp lens for a tiny
>> format than for a larger format.

>
> Are you claiming that the lens in that camera is going to provide any
> decent contrast at even 150 lp/mm (at less than f/5.6), or do they just
> cover it up with excessive sharpening after the fact?


Basically, yes. The better P&S dcams actually work.

Download the original of the London Bridge shot in the Oly 8080 gallery.
It's not grossly bad, and not grossly oversharpened.

http://www.dpreview.com/gallery/olympusc8080wz_samples/

> Macro pictures with a 1.6x body and an EF-S 60mm macro lens completely
> blow away anything I've seen P&S cameras do. Of course, a good part of
> that is the fact that it's a true macro lens, not a zoom lens with a
> supposed "macro" mode, but since the P&S can't have the lens changed, that
> is a valid point.


Yes. The P&S camera macro modes are usually a disaster.

> At f/5.6, the airy disc is 7.5 microns, with the pixels being just a
> little larger than 2 microns, so the airy disc from a point would cover 3
> full pixels. That doesn't sound like 50% MTF to me, but we're getting
> into an area that I'm less familiar with.


The 800/(f stop) estimate for 50% MTF is pretty common, although I don't
have a definitive reference at hand. It's an estimate, though, and there are
different versions, from 700/(f stop) to 850 or 900/(f stop).

David J. Littleboy
Tokyo, Japan


 
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Steve Wolfe
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      07-05-2006
>> Are you claiming that the lens in that camera is going to provide any
>> decent contrast at even 150 lp/mm (at less than f/5.6), or do they just
>> cover it up with excessive sharpening after the fact?

>
> Basically, yes. The better P&S dcams actually work.
>
> Download the original of the London Bridge shot in the Oly 8080 gallery.
> It's not grossly bad, and not grossly oversharpened.
>
> http://www.dpreview.com/gallery/olympusc8080wz_samples/


I see much more sharpening than I have to use for my RebXT (and thus, more
artifacts), and still not as much detail. In fact, looking at it again,
over-sharpening is even more evident in the diagonals. That image really
doesn't appear to me that the lens is providing anywhere near the resolution
of the sensor.


steve


 
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bugbear
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      07-05-2006
MikeM wrote:
> My C-7070 gets to 1.2 ", but with no flash, and most of my subjects
> avoid bright light and are in positions that make using a tripod a
> problem


Your answer may be a different tripod?

Benbo or unilock?

BugBear
 
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Bob Williams
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      07-05-2006


MikeM wrote:
> I'm new to digital and don't know much about them. I have an Olympus
> C-7070 and have been taking close-ups of plant structures like growing
> points and have noticed that when I view the images at 100 % there
> have been very small insects that the 7.1 MP of my camera are not
> quite enough to get good detail of. I use macro a lot so I was
> thinking of trying to get a camera with more pixels. If I understand
> correctly, the more pixels on a sensor of a given size, the more noise
> becomes a problem. I have read that just going for the highest number
> of MPs I can afford is not the best way to decide on a camera so I
> would like to know if there are any cameras/brands that are better at
> increasing the MPs while controlling the noise.
>
> Thanks
> Mike



A 7MP picture taken from 1.2 inches away should produce some pretty
awesome macro images. The 7070 has an attenuated flash mode for close
ups that should be some help. If the camera gets in the way of the flash
at that close a distance, try aiming the flash at a piece of white paper
angled so the paper diffuses light onto your subject. Alternatively
you can use an off-camera flash to illuminate the subject without
interference from the camera.

It is not paucity of Megapixels that is preventing you from getting the
shot you want. Extreme Close-up photography is not a walk in the park.
You will have to experiment with different shooting techniques.
Bob

 
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