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Author Topic: Pixelsize and depth-of-field  (Read 28291 times)
henrikfoto
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« on: May 25, 2008, 03:34:09 PM »
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Is it right to assume that the optimum setup to increase depth-of-field would be a sensor with big pixels? Isnīt it correct that these bigger pixels allow smaller f-stops without diffraction than the smaller ones?

So if you donīt need to make very large prints, would you be better of with a 6 or 11 mp digital back than the never ones with pixel-sizes of 9 or 7,2 microns? For example in product photography if you want the depth-of-field to be as large as possible, and would need to work on f22 or higher.

Anybody who knows or have tested? Which of the backs have larges pixels than 9 micron?

Henrik
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newrooky
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« Reply #1 on: May 25, 2008, 03:48:57 PM »
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Is it right to assume that the optimum setup to increase depth-of-field would be a sensor with big pixels? Isnīt it correct that these bigger pixels allow smaller f-stops without diffraction than the smaller ones? 

So if you donīt need to make very large prints, would you be better of with a 6 or 11 mp digital back than the never ones with pixel-sizes of 9 or 7,2 microns? For example in product photography if you want the depth-of-field to be as large as possible, and would need to work on f22 or higher.

Anybody who knows or have tested? Which of the backs have larges pixels than 9 micron?

Henrik
[a href=\"index.php?act=findpost&pid=197924\"][{POST_SNAPBACK}][/a]


Henrik,

Pixel size does not have a direct correlation to depth of field from what i know.  The size of the overall sensor is what contributes to the difference in depth of field that you see.  If you want the greatest depth of field, you would logically be better off shooting with a smaller chip (however, generally you find a decrease in file quality for the same Mpix).  

The bigger the sensor/film size is, the shallower the depth of field you will get at the same F-stop.    

To reiterate, if you have a 20micron chip spread over 56x56 and a 7 micron chip spread over 56x56, then the depth of field will be the same if they are sampled to the same output size.

If you were very concerned with achieving very large depth of field and the best image quality was not required, i suppose you could consider using a smaller chip size if you were not into using tilt/shift techniques or other workarounds.
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Graham Mitchell
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« Reply #2 on: May 25, 2008, 03:55:26 PM »
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Pixel size DOES affect DOF. Just reduce a 22MP image down to 0.2MP for a web sized image and suddenly the whole image looks to be in focus (unless you have some serious foreground/background blur) because the 'in focus' and 'nearly in focus' areas of the image will both appear in focus at the reduced size. This is exactly how the image would appear if shot on a 0.2MP sensor the same size as the original.

There are disagreements about what constitutes DOF: Personally I find the traditional film-based definition inadequate, and prefer to think of it as what appears in focus when viewed on screen at 100% (traditionalists will no doubt object strongly).

Example. At full size, the DOF is only half a metre. At this size, the whole image looks in focus.

« Last Edit: May 25, 2008, 04:06:47 PM by foto-z » Logged

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henrikfoto
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« Reply #3 on: May 25, 2008, 03:56:28 PM »
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Henrik,

Pixel size does not have a direct correlation to depth of field from what i know.  The size of the overall sensor is what contributes to the difference in depth of field that you see.  If you want the greatest depth of field, you would logically be better off shooting with a smaller chip (however, generally you find a decrease in file quality for the same Mpix). 

The bigger the sensor/film size is, the shallower the depth of field you will get at the same F-stop.   

To reiterate, if you have a 20micron chip spread over 56x56 and a 7 micron chip spread over 56x56, then the depth of field will be the same if they are sampled to the same output size.

If you were very concerned with achieving very large depth of field and the best image quality was not required, i suppose you could consider using a smaller chip size if you were not into using tilt/shift techniques or other workarounds.
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Hi!

Thanks, I understand that. What I am really wondering about is if itīs correct that the
larger pixels allow smaller appertures without the same loss of quality caused by diffraction
at the sensor?

I use tilt and shift, but that is not always the solution.

Henrik
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Frank Doorhof
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« Reply #4 on: May 25, 2008, 04:15:53 PM »
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Google on circle of confusion that will give you some information.
And it translates to the webexample also  
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henrikfoto
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« Reply #5 on: May 25, 2008, 04:27:16 PM »
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Google on circle of confusion that will give you some information.
And it translates to the webexample also 
[a href=\"index.php?act=findpost&pid=197937\"][{POST_SNAPBACK}][/a]


Hi Frank!

I know about this, but all never digital lenses are best at f.8 (about), because the pixels they are made for are so small. Used at f.22 or higher the quality of the image hurts. Wouldnīt larger pixels allow these smaller apertures with less quality-loss?

Henrik
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newrooky
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« Reply #6 on: May 25, 2008, 04:52:39 PM »
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Pixel size DOES affect DOF. Just reduce a 22MP image down to 0.2MP for a web sized image and suddenly the whole image looks to be in focus (unless you have some serious foreground/background blur) because the 'in focus' and 'nearly in focus' areas of the image will both appear in focus at the reduced size. This is exactly how the image would appear if shot on a 0.2MP sensor the same size as the original.


I am by no means an expert on the matter, but i have a hard time believing the circle of confusion on that image accounts for 1/2 meter dof. As mentioned, i am not an expert but i would like to see the exif for the image and such.

As for downsizing images images, pixel size does not effect DOF.  In fact, you just said so.  The 22mp image downsized to make an even comparison with the .2mp one, both with the same sensor size, will create the same image.  Hence, pixel size does not have an effect on dof.

If i am wrong please correct me.
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« Reply #7 on: May 25, 2008, 04:59:01 PM »
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The DoF depends on the focal length, focusing distance, aperture diameter and circle of confusion. The CoC depends on the pixel size.

Small P&S have large DoF because of the miniscule focal length, which more than makes up for the tiny pixels.

Larger pixels increase the CoC (and thereby the DoF); they tolerate smaller apertures as well (higher diffraction) - however, they yield lower resolution.

The sensor size has nothing to do with DoF but with FoV, the angle of view.
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« Reply #8 on: May 25, 2008, 04:59:24 PM »
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I am by no means an expert on the matter, but i have a hard time believing the circle of confusion on that image accounts for 1/2 meter dof. As mentioned, i am not an expert but i would like to see the exif for the image and such.

As for downsizing images images, pixel size does not effect DOF.  In fact, you just said so.  The 22mp image downsized to make an even comparison with the .2mp one, both with the same sensor size, will create the same image.  Hence, pixel size does not have an effect on dof.

If i am wrong please correct me.
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No, it should not have a direct effect, but larger pixels should allow smaller appertures and therefore larger DOF??

Henrik
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Graham Mitchell
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« Reply #9 on: May 25, 2008, 05:11:26 PM »
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As for downsizing images images, pixel size does not effect DOF.  In fact, you just said so.  The 22mp image downsized to make an even comparison with the .2mp one, both with the same sensor size, will create the same image.  Hence, pixel size does not have an effect on dof.
[a href=\"index.php?act=findpost&pid=197945\"][{POST_SNAPBACK}][/a]

You are comparing a 0.2 MP image with another 0.2MP image

If you printed the 0.2MP image and the 22 MP images at the same size, the 0.2 MP image would appear to be in focus all over. The 22MP image would not.
« Last Edit: May 25, 2008, 05:13:41 PM by foto-z » Logged

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henrikfoto
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« Reply #10 on: May 25, 2008, 05:14:06 PM »
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The DoF depends on the focal length, focusing distance, aperture diameter and circle of confusion. The CoC depends on the pixel size.

Small P&S have large DoF because of the miniscule focal length, which more than makes up for the tiny pixels.

Larger pixels increase the CoC (and thereby the DoF); they tolerate smaller apertures as well (higher diffraction) - however, they yield lower resolution.

The sensor size has nothing to do with DoF but with FoV, the angle of view.
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But is more than 6 or 11 mp on a mediumformat system needed for prints at A4? Would anybody notice the difference between the newer backs at A4?
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Kirk Gittings
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« Reply #11 on: May 25, 2008, 05:32:09 PM »
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This where you guys lose me. Going back to film. back when I was shooting film, I oftentimes shot a 35mm slide to accompany my 4x5 transparencies. Roughly with lenses of similar FoV, I could shoot at f8 on the 35 to get approximately the same DoF as f22 on the 4x5. If I shot at f22 on the 35, I would have significantly more DoF than the 4x5. I see the same thing on a 30D vs. a 5D.
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« Reply #12 on: May 25, 2008, 05:37:38 PM »
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This where you guys lose me. Going back to film. back when I was shooting film, I oftentimes shot a 35mm slide to accompany my 4x5 transparencies. Roughly with lenses of similar FoV, I could shoot at f8 on the 35 to get approximately the same DoF as f22 on the 4x5. If I shot at f22 on the 35, I would have significantly more DoF than the 4x5. I see the same thing on a 30D vs. a 5D.
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Kirk, you are comparing different 'sensor' sizes, not 'pixel' sizes.

Actually with the same film stock in both cameras, your pixel size is effectively even, just the sensor size is different.

This thread is about pixel size.
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henrikfoto
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« Reply #13 on: May 25, 2008, 05:41:48 PM »
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Kirk, you are comparing different 'sensor' sizes, not 'pixel' sizes.

Actually with the same film stock in both cameras, your pixel size is effectively even, just the sensor size is different.

This thread is about pixel size.
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Would you say that a combination of small sensor-size and large pixels would result in the largest depth-of-field? (combined with small apperture of course)
« Last Edit: May 25, 2008, 05:44:06 PM by henrikfoto » Logged
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« Reply #14 on: May 25, 2008, 06:00:59 PM »
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when I was shooting film, I oftentimes shot a 35mm slide to accompany my 4x5 transparencies. Roughly with lenses of similar FoV, I could shoot at f8 on the 35 to get approximately the same DoF as f22 on the 4x5
The same FoV on a 4x5 camera requires 1.5 times longer focal length than on the 36mm. Therefor the DoF is less on the MF camera than on the 36mm, assuming the same f-number; you have to compensate for that by smaller aperture.
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« Reply #15 on: May 25, 2008, 06:34:41 PM »
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You are comparing a 0.2 MP image with another 0.2MP image

If you printed the 0.2MP image and the 22 MP images at the same size, the 0.2 MP image would appear to be in focus all over. The 22MP image would not.
[a href=\"index.php?act=findpost&pid=197950\"][{POST_SNAPBACK}][/a]


This is not true.

If i take a 56x56 sensor that is .2mpx and another of the same size that is 22mpx, then when i print it out at the same size, say 4x6, the DOF will be identical.  
If not what makes you think so?

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The sensor size has nothing to do with DoF but with FoV, the angle of view.
[a href=\"index.php?act=findpost&pid=197946\"][{POST_SNAPBACK}][/a]

Agreed, however, in order to have the same fov on 2 cameras with different sensor sizes, you must adjust the lens' focal length.  This in effect changes the DOF.

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Would you say that a combination of small sensor-size and large pixels would result in the largest depth-of-field? (combined with small apperture of course)
[a href=\"index.php?act=findpost&pid=197956\"][{POST_SNAPBACK}][/a]


I would still say that a smaller sensor with the same fov as a larger sensor is the only way to adjust the sensor to get more dof.  I am having a very hard time understanding how pixel size changes DOF at all, so if someone knows how it does please explain.  

As far as the main question of this topic goes:  Would a sensor with larger photosites somehow reduce the diffraction of lenses when stopping down smaller than f22? (i think that is the question)  My understanding is that this is a limitation of the lens and not a limitation of the sensor and therefore is not something that can be remedied by changing sensitivity and size of the photosites.   The higher the aperture you go to (beyond the optimal point) the less lines the lens will be able to resolve and definition will be lacking.   i think.  



BTW i still don't understand (nor believe) how larger photosites/pixel determine anything having to do with DOF, so if it does feel free to give me a heads up with a logical explanation.

-b-
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« Reply #16 on: May 25, 2008, 06:44:52 PM »
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This is not true.

If i take a 56x56 sensor that is .2mpx and another of the same size that is 22mpx, then when i print it out at the same size, say 4x6, the DOF will be identical.   
If not what makes you think so?
[a href=\"index.php?act=findpost&pid=197961\"][{POST_SNAPBACK}][/a]

Well I am not sure how to make it any clearer. I have already posted the 0.2MP image, and you can see that the DOF is effectively infinite. Compared to this, the 22MP image printed at the same size would have very sharp details and (relatively) blurred areas. The eye sees the resolution of the sharpest parts on an image and anything less sharp is seen as out of focus. It is a relative measure.
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« Reply #17 on: May 25, 2008, 06:49:07 PM »
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Well I am not sure how to make it any clearer. I have already posted the 0.2MP image, and you can see that the DOF is effectively infinite. Compared to this, the 22MP image printed at the same size would have very sharp details and (relatively) blurred areas. The eye sees the resolution of the sharpest parts on an image and anything less sharp is seen as out of focus. It is a relative measure.
[a href=\"index.php?act=findpost&pid=197963\"][{POST_SNAPBACK}][/a]


What is the exif data for the photo above?

mainly camera, focal length, fstop, and focusing distance/subject distance.
« Last Edit: May 25, 2008, 06:51:00 PM by newrooky » Logged

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« Reply #18 on: May 25, 2008, 07:15:01 PM »
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Agreed, however, in order to have the same fov on 2 cameras with different sensor sizes, you must adjust the lens' focal length.  This in effect changes the DOF
It is unhealty for a discussion to mix up different aspects. Stick to narrow subjects, abstracted from others; otherwise we end up with arguments like my eyes are not as good as yours, so the DoF for me is much larger than for you.

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I am having a very hard time understanding how pixel size changes DOF at all
Well, then back to the basics.

What does it mean to be in focus? It means, that different light rays from a point of light meet at the focal plane (at the level of the film or sensor). Out of focus means, that the light rays meet before or (imaginarily) after the focal plane; anyway, they arrive at different points on the focal plane.

When these points are so close, that the difference is not perceivable, then we say they are within the circle of confusion.

Thie means with sensors, that as long as the light rays arrive within the "catchment area of the pixel site" (i.e. over the microlens of a single pixel), then one can not differentiate between in-focus and out-of-focus. However, if some of the light rays arrive at other pixels, then that point of light appears to be at several pixels at the same time.

So, the larger the pixel site, the larger difference is tolerable.
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Gabor
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« Reply #19 on: May 25, 2008, 07:17:56 PM »
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What is the exif data for the photo above?

mainly camera, focal length, fstop, and focusing distance/subject distance.
[a href=\"index.php?act=findpost&pid=197964\"][{POST_SNAPBACK}][/a]

The Rollei camera doesn't communicate that info to the back so I don't have any EXIF info.

It is beside the point anyway. No aperture that I could have used could get all of that image in equally good focus across 22 MP.

The 22MP v 0.2 MP example is an extreme one, but just demonstrates clearly the effect that pixel size has on focus.
« Last Edit: May 25, 2008, 07:24:14 PM by foto-z » Logged

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