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Math question - sort of



 
 
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  #11  
Old September 23rd 09, 08:28 PM posted to rec.photo.equipment.35mm,rec.photo.digital,rec.photo.digital.slr-systems
Andrey Tarasevich
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Posts: 70
Default Math question - sort of

John McWilliams wrote:

It's not just about the maths. Way too many other factors affecting IQ,
and I suspect most photographers will soon forget about how equivalent
one framing on one camera is to another body he's used. He'll go for the
highest IQ he can in the moment.


IQ is IQ. But the question the OP posted is about the _math_, as he
stated in the subject. Also, the way it is formulated in the message
body, it is about the math and math alone.

I think the OP knows perfectly well that the IQ is not just about the
math, which is why he made a specific effort to extract and isolate just
the math part of the problem in his question.
  #12  
Old September 23rd 09, 08:52 PM posted to rec.photo.equipment.35mm,rec.photo.digital,rec.photo.digital.slr-systems
nospam
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Posts: 24,165
Default Math question - sort of

In article , John Navas
wrote:

I don't think that my 10D was pushing up against the resolution limit of my
400 f/5.6L and while I may not realize the all the resolving potential with
that lens on the 7D, I was more interested in the difference in potential
resolution, the conversion puzzle and not so much the practicality, i.e.,
don't spoil my fun!


If we assume a top (not cheap) non-zoom telephoto lens will resolve 80
LPM (check the MTF charts for your lens), then the maximum resolution of
the lens on a Canon APS-C sensor of 22.3 mm x 14.9 mm (like the 7D) is
22.3 x 80 x 2 x 14.9 x 80 x 2 = 8.5 MP, far less than the 18 MP spec of
the 7D, and anything more is wasted.


nonsense. there is a very clear and visible difference between an 8 mp
camera such as a canon 20d and an 18 mp camera such as a canon 7d.

dpreview measured the resolution of the 8mp 20d at 1850/1650 lines and
the 15 mp 500d at 2400/2350 lines (the 7d has not yet been reviewed).
moving up to the 24 megapixel nikon d3x, it's 2700/2600 lines. if the
excess megapixels beyond 8 were wasted there would be no difference,
yet there is.

http://www.dpreview.com/reviews/canoneos20d/page27.asp
http://www.dpreview.com/reviews/canoneos500d/page28.asp
http://www.dpreview.com/reviews/nikond3x/page32.asp
  #13  
Old September 23rd 09, 09:18 PM posted to rec.photo.equipment.35mm,rec.photo.digital,rec.photo.digital.slr-systems
Eric Miller
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Posts: 181
Default Math question - sort of


"Andrey Tarasevich" wrote in message
...


I think the OP knows perfectly well that the IQ is not just about the
math, which is why he made a specific effort to extract and isolate just
the math part of the problem in his question.


You read me well.

Eric Miller
www.dyesscreek.com

"When the only tool you have is a hammer, every problem begins to resemble a
nail." - Abraham Maslow


  #14  
Old September 24th 09, 12:49 AM posted to rec.photo.equipment.35mm,rec.photo.digital,rec.photo.digital.slr-systems
John Sheehy
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Posts: 878
Default Math question - sort of

John Navas wrote in
:


If we assume a top (not cheap) non-zoom telephoto lens will resolve 80
LPM (check the MTF charts for your lens), then the maximum resolution
of the lens on a Canon APS-C sensor of 22.3 mm x 14.9 mm (like the 7D)
is 22.3 x 80 x 2 x 14.9 x 80 x 2 = 8.5 MP, far less than the 18 MP
spec of the 7D, and anything more is wasted.


Aliased imaging ... shift everything 1/2 pixel horizontally and vertically,
and what do you get? Gray nothing.

It takes *SIX* pixels, exclusive, to properly sample a line pair.

And there is usable contrast at much higher than 80 LP/mm with a lens like
the 400mm f/5.6, especially if the noise is low and you can sharpen
aggressively.

  #15  
Old September 24th 09, 02:07 AM posted to rec.photo.equipment.35mm,rec.photo.digital,rec.photo.digital.slr-systems
John Sheehy
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Posts: 878
Default Math question - sort of

Eric Miller wrote in
:

I went from the 10D to the 5D. When I had my 10D, I learned to like
the 1.6x way of fooling myself into thinking my 400mm lens was a 560mm
lens.


I don't find that a very useful way of looking at things.

A lens is the focal length that it really is. The *sensor* captures a
certain area of the focal plane, with certain potential MTF curves,
depending on sensel spacing, effective fill factor (photosite or
microlens, whichever is wider), and AA filter strength. The size of the
sensor, combined with the focal length, determine the *breadth* of the
capture, IMO, and the term "reach" (which, also IMO, is poorly
selected), if used at all, should be related to the pixel spacing and
pixel qualities rather than the "crop factor". A 5D2 with the same lens
has more "reach" than a 10D, in the sense that it puts the subject over
more pixels. Going by crop factors, one might erroneously assume that
the 10D will get you more subject detail.

Now I am thinking of getting myself another birding camera and am
trying to figure out if there is a way to think of resolution as
effective focal length versus the 10D. So, for example, if I were to
get a 7D at 18 megapixels how would that compare to 10D resolution
wise in terms of what focal length lens would I have had to put on the
10D to get a 5 inch tall bird at 20 meters (or any distance) to be
rendered by the same number of pixels (one dimension only or my head
will hurt too much) on the 10D that it would be rendered on the 7D
using the 400mm lens.


I would just think of it as 400mm, same FOV, but with higher subject
resolution and less subject noise.
  #16  
Old September 24th 09, 07:45 AM posted to rec.photo.equipment.35mm,rec.photo.digital,rec.photo.digital.slr-systems
nospam
external usenet poster
 
Posts: 24,165
Default Math question - sort of

In article , John Navas
wrote:

If we assume a top (not cheap) non-zoom telephoto lens will resolve 80
LPM (check the MTF charts for your lens), then the maximum resolution of
the lens on a Canon APS-C sensor of 22.3 mm x 14.9 mm (like the 7D) is
22.3 x 80 x 2 x 14.9 x 80 x 2 = 8.5 MP, far less than the 18 MP spec of
the 7D, and anything more is wasted.


nonsense. there is a very clear and visible difference between an 8 mp
camera such as a canon 20d and an 18 mp camera such as a canon 7d.


That depends on the lens.


"assume a top (not cheap) non-zoom telephoto lens"

Read what I wrote more carefully.


likewise.
  #17  
Old September 25th 09, 10:10 PM posted to rec.photo.equipment.35mm,rec.photo.digital,rec.photo.digital.slr-systems
Charles[_2_]
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Posts: 695
Default Math question - sort of

Let the reader decide:

http://www.luminous-landscape.com/tu...solution.shtml


  #18  
Old September 25th 09, 11:35 PM posted to rec.photo.equipment.35mm,rec.photo.digital,rec.photo.digital.slr-systems
Kennedy McEwen
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Posts: 639
Default Math question - sort of

In article , Andrey Tarasevich
writes
John McWilliams wrote:
It's not just about the maths. Way too many other factors affecting
IQ, and I suspect most photographers will soon forget about how
equivalent one framing on one camera is to another body he's used.
He'll go for the highest IQ he can in the moment.


IQ is IQ. But the question the OP posted is about the _math_, as he
stated in the subject. Also, the way it is formulated in the message
body, it is about the math and math alone.

If it is just about the math then you need to quantify the lens quality
contribution as well - your math is less than half the story, dealing
only with pixel geometry.

To include the lens contribution you need to use significantly more
complex math, convolving pixel geometry with lens aberration geometry,
or a completely different type of math using pixel MTF and lens MTF to
scale resolved spatial resolutions at equal contrast. That is what the
discussion on the LL site is trying to explain.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's ****ed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)
  #19  
Old September 26th 09, 12:40 AM posted to rec.photo.equipment.35mm,rec.photo.digital,rec.photo.digital.slr-systems
Eric Miller[_3_]
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Posts: 11
Default Math question - sort of

Kennedy McEwen wrote:
In article , Andrey Tarasevich
writes
John McWilliams wrote:
It's not just about the maths. Way too many other factors affecting
IQ, and I suspect most photographers will soon forget about how
equivalent one framing on one camera is to another body he's used.
He'll go for the highest IQ he can in the moment.


IQ is IQ. But the question the OP posted is about the _math_, as he
stated in the subject. Also, the way it is formulated in the message
body, it is about the math and math alone.

If it is just about the math then you need to quantify the lens quality
contribution as well


No, the question posed in the original post had nothing to do with that.

- your math is less than half the story, dealing
only with pixel geometry.


That would actually be the whole story, since the original question
strictly concerned the pixels.

To include the lens contribution you need to use significantly more
complex math, convolving pixel geometry with lens aberration geometry,
or a completely different type of math using pixel MTF and lens MTF to
scale resolved spatial resolutions at equal contrast. That is what the
discussion on the LL site is trying to explain.


Pertinence to this thread?

Eric Miller
www.dyesscreek.com
  #20  
Old September 26th 09, 02:08 AM posted to rec.photo.equipment.35mm,rec.photo.digital,rec.photo.digital.slr-systems
Kennedy McEwen
external usenet poster
 
Posts: 639
Default Math question - sort of

In article , Eric Miller
writes
Kennedy McEwen wrote:

If it is just about the math then you need to quantify the lens
quality contribution as well


No, the question posed in the original post had nothing to do with that.

I suggest you read what you wrote in your question again and, in future
ask what you mean or mean what you ask! You specifically refer to
resolution and that is a lot more than just pixel density!

- your math is less than half the story, dealing only with pixel
geometry.


That would actually be the whole story, since the original question
strictly concerned the pixels.

No, you stated: "if there is a way to think of resolution as effective
focal length versus the 10D".

Pixels are only one component of resolution: optics contribute
significantly and, in this particular case, dominate.

Others have tried to explain this to you in the thread, but it is
clearly making your "head hurt too much"!

To include the lens contribution you need to use significantly more
complex math, convolving pixel geometry with lens aberration geometry,
or a completely different type of math using pixel MTF and lens MTF to
scale resolved spatial resolutions at equal contrast. That is what
the discussion on the LL site is trying to explain.


Pertinence to this thread?

If you have to ask that question then the answer is clearly beyond you,
but it is pertinent on at least three counts:
1. It is the full answer to your question, which you clearly seem unable
to understand. Even perfect optics have a finite resolution, and when
the sensor resolution approaches that, which is certainly the case in
the 7D, that needs to be included in any scaling comparison, as
explained in the LL article. The optical resolution is limited in terms
of the minimum blur spot, while the sensor is limited in resolution by
the pixel area. The cameras limits are determined by convolution of
optical blur spot and pixel area. Convolution is a fairly complicated
mathematical procedure and it is simpler to represent these parameters
in terms of MTF curves simplifying the calculation of the camera
resolution as it is just the product of the MTFs. The effective focal
length scaling, in terms of reach, is simply then the ratio of the
spatial resolutions at which the limiting contrast is achieved. That is
the COMPLETE answer to your question. Whether you understand it or not,
pixel scaling is only part of the issue and, in the case of comparing
anything to the high pixel density of the 7D, will yield highly
optimistic scaling on its own.

2. It has already been linked to in this thread, but obviously ignored
by you. I suggest you read it again and make some effort to understand
it before claiming it is irrelevant, since optics dominate the question
you have asked, NOT pixels.

3. Others who read this thread in future, which will be archived
forever, may be less mentally challenged than you and be looking for a
more complete answer, not a simple pixel scaling answer which is trivial
to calculate but optimistic at best and wrong in general.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's ****ed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)
 




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