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Author Topic: What about depth of field?  (Read 2686 times)
Bumpy
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« on: December 02, 2011, 06:02:43 AM »

This a comment for this page on the website
I love DxO mark reviews but there is one area I remain unenlightened (perhaps in both theory and practice).

My understanding is that lens diffraction will result in loss of detail (resolution) at f-stops higher than a mathematically determined point based on pixel pitch.

If I've got things right an APS-C sensor at 16MP does not suffer diffraction until somewhere between F8 and F11, but at 24MP loss of detail begins somewhere between F5.6 and F8.  A FullFrame sensor will, of course, do much better because pixel pitch is larger.

I would *love* to see DxO mark test this.  Seems simple (to my possibly challenged little mind), just shoot resolution chart at successive f-stops and record where diffraction kicks-in and limits or reduces resolution.  Might be hard to normalize as a number and integrate into overall score, but immensely helpful as a photographer to know for each camera where stopping down begins to trade off not only longer exposure but also loss of detail [probably negating any actual DoF improvement].

I mention this here of course because the Nex-7 vs. Nex5-N is a good place to care [what I really want to know is whether I get equal DoF AND better resolution from the N7, or that (at some F-stop) my equal DoF comes at the price of resolution]. So if I do a lot of high f-stop work to maximize DoF perhaps the Nex-7 doesn't actually give me better resolution?  Even more interesting to compare FF to APS-C to get a sense of how much more DoF the FF can capture....

Hope my post isn't too clueless.  In any event keep up the terrific work - DxO is a fabulous resource!

Cheers,

Bumpy.
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ldgt
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« Reply #1 on: December 03, 2011, 04:21:29 PM »

In that aspect, the best possible sensor has only one pixel. Thus it does not lose any details regardless of f-stop. Only problem is, it had none details to start with. The same, but for lesser degree, goes for your comparison of 16 MP and 24 MP sensors.

DXomark results already include diffraction, it would be difficult (and meaningless) to exclude it because they measure real lenses.

If you need large DOF, and avoid diffraction limit at same time, TS lenses or TS adaptor result in a improvement. Picture stacking is another way. Pixel size, or sensor size has nothing to do with diffraction because it occurs within lens.
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appliance
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« Reply #2 on: December 24, 2011, 12:14:10 AM »

<div id="linkdxomark">This a comment for <a href="http://www.dxomark.com/index.php/Cameras/Camera-Sensor-Database/Sony/NEX-7">this page on the website</a></div>I love DxO mark reviews but there is one area I remain unenlightened (perhaps in both theory and practice).

My understanding is that lens diffraction will result in loss of detail (resolution) at f-stops higher than a mathematically determined point based on pixel pitch.

If I've got things right an APS-C sensor at 16MP does not suffer diffraction until somewhere between F8 and F11, but at 24MP loss of detail begins somewhere between F5.6 and F8.  A FullFrame sensor will, of course, do much better because pixel pitch is larger.

I would *love* to see DxO mark test this.  Seems simple (to my possibly challenged little mind), just shoot resolution chart at successive f-stops and record where diffraction kicks-in and limits or reduces resolution.  Might be hard to normalize as a number and integrate into overall score, but immensely helpful as a photographer to know for each camera where stopping down begins to trade off not only longer exposure but also loss of detail [probably negating any actual DoF improvement].

I mention this here of course because the Nex-7 vs. Nex5-N is a good place to care [what I really want to know is whether I get equal DoF AND better resolution from the N7, or that (at some F-stop) my equal DoF comes at the price of resolution]. So if I do a lot of high f-stop work to maximize DoF perhaps the Nex-7 doesn't actually give me better resolution?  Even more interesting to compare FF to APS-C to get a sense of how much more DoF the FF can capture....

Hope my post isn't too clueless.  In any event keep up the terrific work - DxO is a fabulous resource!

Cheers,

Bumpy.


Diffraction is a function of the shape and size of the lens aperture.  It's relation to sensors is in terms of size:  a smaller sensor has to be magnified  more to create an equivalent sized image;  thus the circle of confusion is also magnified.  As far as I know it's not related to pixel pitch.
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Stephen123
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« Reply #3 on: December 28, 2011, 09:49:36 PM »

The circle of least confusion is the smallest spot that a lens can produce.  Isn't the circle of least confusion effected by aperture? And doesn't it matter when it exceeds the pixel pitch?  I think Bumpy has a good point.
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