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Thread started 10 Feb 2013 (Sunday) 16:55
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Why does FF yield shallower DOF?

 
Snowyman
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Feb 12, 2013 06:10 |  #121

The "Circle of Confusion" is a very precise means of examining and understanding the "Human Condition".

Following this thread is a very austere Zen exercise. ;)


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Feb 12, 2013 06:46 |  #122

Snowyman wrote in post #15601159 (external link)
The "Circle of Confusion" is a very precise means of examining and understanding the "Human Condition".

Following this thread is a very austere Zen exercise. ;)

It seems to be more of an exercise in how when people don't understand a complicated set of formulas and the factors that make them up, they simplify it down to 2-3 of the factors they do understand and disregard the rest, and in some cases belittle those that that try to help explain the other factors. I am sure there is a psychological term for this "concept simplification".

I have to deal with it everyday in our office, there are those on the executive side that don't understand the CS side of the business, and you have to distill the issues at hand down to just 2 or 3 key factors, and just give up explaining the other factors, and hope for the best. "It would seem easy to just add a field here on the grid".... and 20 hours later they want to know why it took so long, and who was the person that took too long. This discussion feels just like those discussions. ;)

Happens all the time in technology, politics, financials, etc. :D


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Feb 12, 2013 06:58 |  #123

TeamSpeed wrote in post #15601208 (external link)
It seems to be more of an exercise in how when people don't understand a complicated set of formulas and the factors that make them up, they simplify it down to 2-3 of the factors they do understand and disregard the rest, and in some cases belittle those that that try to help explain the other factors. I am sure there is a psychological term for this "concept simplification".

Otherwise known as "Confirmation Bias". The process of arriving at a conclusion, then ignoring, manipulating or attempting to discredit any evidence that disproves it.




  
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Feb 12, 2013 07:15 |  #124

JohnB57 wrote in post #15601229 (external link)
Otherwise known as "Confirmation Bias". The process of arriving at a conclusion, then ignoring, manipulating or attempting to discredit any evidence that disproves it.

Which then leads to... which is why these threads always, always, always go so long when they get posted. :D

Backfire effect

A similar cognitive bias found in individuals is the Backfire effect. Here, individuals challenged with evidence contradictory to their beliefs tend to reject the evidence and instead become an even firmer supporter of the initial belief.[32][33] The phrase was first coined by Brendan Nyhan and Jason Reifler in a paper entitled "When Corrections Fail: The persistence of political misperceptions".[34]


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Feb 12, 2013 07:22 |  #125

SkipD wrote in post #15601023 (external link)
This total misunderstanding of depth of field is probably typical for many (if not most) folks.


Depth of field is NOT (and can not be) "measured". It is calculated with a rather complex formula which uses several assumed variables. The assumed variables include:
  • assignment of a standard size for a print that would be viewed by people
  • assignment of the standard distance from which they would view the standard sized print
  • an assumed standard visual acuity of the people viewing the print
  • how large a blur the viewers of the print would be likely to interpret as a point vs interpret as a blur
Then, the assumed minimum blur size is reduced to the size that it would be on the film or the in-camera image on a digital sensor to get the "circle of confusion" variable in the formula. Then they have to deal with the optics that involves focal length, distance to the "subject", and more.

I don't pretend to fully understand the mathematics involved in the formulae, but I understand enough to know why the camera format (size of the film frame or digital sensor in a camera) is one very important factor in calculating depth of field.

That's a good answer, thanks.

Being able to calculate it is like saying you can measure it since you still get some kind of reading. A definite number. A number which specifies distance.

How i perceive DOF is:
How much of real life scene's depth is actually going to be in (acceptable) focus. Like things that were between 5 and 6 feat away from the camera are sharp. Indeed that changes if you view the image at different magnifications.

So if you have two cameras with different sensor sizes but same lenses placed next to each other taking the same picture. You print that picture at the same magnification (meaning two different sizes of pictures) and you get exactly the same DOF. If you print them to be the same size, picture wich was taken by a bigger sensor will be less magnified and DOF will appear less shallow (circle of confusion). Now in real life situations where you are aiming for a picture and want to get the same framing for bigger sensor you get closer to the subject or use a longer focal length lense. That gets you shallower DOF.

I'm just hoping that's not a total misunderstanding of DOF...


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Feb 12, 2013 07:31 |  #126

marsaz wrote in post #15601282 (external link)
So if you have two cameras with different sensor sizes but same lenses placed next to each other taking the same picture. You print that picture at the same magnification (meaning two different sizes of pictures) and you get exactly the same DOF. If you print them to be the same size, picture wich was taken by a bigger sensor will be less magnified and DOF will appear less shallow (circle of confusion). Now in real life situations where you are aiming for a picture and want to get the same framing for bigger sensor you get closer to the subject or use a longer focal length lense. That gets you shallower DOF.

I'm just hoping that's not a total misunderstanding of DOF...

This is pretty much on target.

What a lot of folks don't realize is that depth of field changes when one prints or displays images at different sizes, regardless what the available DOF calculators show for distances.


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Feb 12, 2013 07:48 as a reply to  @ SkipD's post |  #127

DOF itself is a funny thing in that it is a really fuzzy, subjective thing that we can calculate with great precision. This precision makes people forget just what kinds of assumptions we are making.

LOL! I remember in the 70s when the US Air Force was transitioning from English to Metric in many things. We had to go through our databases and make direct conversions of a lot of measurements, and our marching orders were to calculate the conversion down to two decimal places.

What made it absurd was that the original figures we had were usually approximations--and sometimes pretty gross approximations, and even stated as much. So "approximately 100 yards" (which was really anything from 95 to 105 yards) was re-entered as "approximately 91.44 meters."

No doubt, years later someone used that number thinking it was correct to approximately one centimeter.


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Feb 12, 2013 07:50 |  #128

marsaz wrote in post #15601282 (external link)
That's a good answer, thanks.

Being able to calculate it is like saying you can measure it since you still get some kind of reading. A definite number. A number which specifies distance.

How i perceive DOF is:
How much of real life scene's depth is actually going to be in (acceptable) focus. Like things that were between 5 and 6 feat away from the camera are sharp. Indeed that changes if you view the image at different magnifications.

So if you have two cameras with different sensor sizes but same lenses placed next to each other taking the same picture. You print that picture at the same magnification (meaning two different sizes of pictures) and you get exactly the same DOF. If you print them to be the same size, picture wich was taken by a bigger sensor will be less magnified and DOF will appear less shallow (circle of confusion). Now in real life situations where you are aiming for a picture and want to get the same framing for bigger sensor you get closer to the subject or use a longer focal length lense. That gets you shallower DOF.

I'm just hoping that's not a total misunderstanding of DOF...

http://www.cambridgein​colour.com/tutorials/d​epth-of-field.htm (external link)

Cambridge in Color gives a good and clear explanation, but take time to read the entire treatise.

Depth of field refers to the range of distance that appears acceptably sharp. It varies depending on camera type, aperture and focusing distance, although print size and viewing distance can also influence our perception of depth of field.

Since there is no critical point of transition, a more rigorous term called the "circle of confusion" is used to define how much a point needs to be blurred in order to be perceived as unsharp. When the circle of confusion becomes perceptible to our eyes, this region is said to be outside the depth of field and thus no longer "acceptably sharp."

When does the circle of confusion become perceptible to our eyes? An acceptably sharp circle of confusion is loosely defined as one which would go unnoticed when enlarged to a standard 8x10 inch print, and observed from a standard viewing distance of about 1 foot.

At this viewing distance and print size, camera manufactures assume a circle of confusion is negligible if no larger than 0.01 inches (when enlarged). As a result, camera manufacturers use the 0.01 inch standard when providing lens depth of field markers (shown below for f/22 on a 50mm lens). In reality, a person with 20-20 vision or better can distinguish features 1/3 this size or smaller, and so the circle of confusion has to be even smaller than this to achieve acceptable sharpness throughout.

A different maximum circle of confusion also applies for each print size and viewing distance combination. In the earlier example of blurred dots, the circle of confusion is actually smaller than the resolution of your screen for the two dots on either side of the focal point, and so these are considered within the depth of field. Alternatively, the depth of field can be based on when the circle of confusion becomes larger than the size of your digital camera's pixels.


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Feb 12, 2013 07:55 |  #129

RDKirk wrote in post #15601347 (external link)
LOL! I remember in the 70s when the US Air Force was transitioning from English to Metric in many things. We had to go through our databases and make direct conversions of a lot of measurements, and our marching orders were to calculate the conversion down to two decimal places.

What made it absurd was that the original figures we had were usually approximations--and sometimes pretty gross approximations, and even stated as much. So "approximately 100 yards" (which was really anything from 95 to 105 yards) was re-entered as "approximately 91.44 meters."

No doubt, years later someone used that number thinking it was correct to approximately one centimeter.

Warning! You've opened the door to another 100 posts on the definition of significant figures! :)


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Feb 12, 2013 07:59 |  #130

RDKirk wrote in post #15601347 (external link)
LOL! I remember in the 70s when the US Air Force was transitioning from English to Metric in many things. We had to go through our databases and make direct conversions of a lot of measurements, and our marching orders were to calculate the conversion down to two decimal places.

What made it absurd was that the original figures we had were usually approximations--and sometimes pretty gross approximations, and even stated as much. So "approximately 100 yards" (which was really anything from 95 to 105 yards) was re-entered as "approximately 91.44 meters."

No doubt, years later someone used that number thinking it was correct to approximately one centimeter.

The example I give when tutoring my kids in significant figures is thus:

I have a circle with a radius of about 3 inches. What is the best answer for the area of this circle:
A - 28.27431 square inches
B - 27 square inches
C - 30 square inches

The best answer is C, becuase it (which can be written as 3 x 10) does not imply any more knowledge of the radius than we have.


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Feb 12, 2013 07:59 |  #131

SkipD wrote in post #15601303 (external link)
This is pretty much on target.

What a lot of folks don't realize is that depth of field changes when one prints or displays images at different sizes, regardless what the available DOF calculators show for distances.

Phew, i was starting to get confused :)

RDKirk wrote:
<...>

I'll take a look at that, thanks. Men usually get too hung up on comparing numbers and technical stuff but I like to know how stuff works. Still need to go and take more pictures though :)


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Feb 12, 2013 08:19 as a reply to  @ marsaz's post |  #132

The best answer...does not imply any more knowledge...than we have.

Expressed in broader philosophical terms.


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Feb 12, 2013 08:25 |  #133

marsaz wrote in post #15601373 (external link)
Phew, i was starting to get confused :)

I'll take a look at that, thanks. Men usually get too hung up on comparing numbers and technical stuff but I like to know how stuff works. Still need to go and take more pictures though :)

JefferyG said this:

This precision makes people forget just what kinds of assumptions we are making.

We get caught up with numbers in this "digital" age, but many people don't realize that in photography (and probably many things) with pre-digital roots, the original assumptions were based on non-numeric empirical observations.

To go on a tangent, I see the same thing happening with the question, "What's the slowest shutter speed I can use with x lens?" People quote and swear by the focal length/shutter speed rule as though it was Einstein's Theory of Relativity...without realizing that the basis of that thumbrule is an assumption of viewing only a 8x10 print (back in the days of film, practically everything was based on the 8x10 print). So when they slavishly shoot with a 200mm lens at 1/200 and get blur at 100% magnification...they figure something must be wrong with the lens, because they certainly used the "right" shutter speed.


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Feb 12, 2013 09:03 |  #134

RDKirk wrote in post #15601437 (external link)
We get caught up with numbers in this "digital" age, but many people don't realize that in photography (and probably many things) with pre-digital roots, the original assumptions were based on non-numeric empirical observations.

To go on a tangent, I see the same thing happening with the question, "What's the slowest shutter speed I can use with x lens?" People quote and swear by the focal length/shutter speed rule as though it was Einstein's Theory of Relativity...without realizing that the basis of that thumbrule is an assumption of viewing only a 8x10 print (back in the days of film, practically everything was based on the 8x10 print). So when they slavishly shoot with a 200mm lens at 1/200 and get blur at 100% magnification...they figure something must be wrong with the lens, because they certainly used the "right" shutter speed.

The immediacy of digital photography is a blessing but also (in a much smaller way) a curse. It has changed the emphasis from the end result to the method. We can analyse and re-analyse our technique in minute detail from the comfort of our office chair seconds after taking the shot. But it has resulted in some of the "observe then measure" concepts such as DoF becoming confused as people no longer think in terms of constants/constraints such as final print size.




  
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Feb 12, 2013 09:05 as a reply to  @ RDKirk's post |  #135

Like I said. You guys are going off topic here. Print size and viewing distance have nothing to do with the full frame vs. crop question. That is entirely something of resolution. Since a crop sensor "may" have more MP density, then your assumptions of another topic would be correct. In the case of the d800 and a 15mp crop camera, there is no difference in COC, when every other factor is equal and the d800 is cropped to 15mp in post.

Just because I do not wish to take this too far off topic, does not mean I do not fully understand the other issues and topics being talked about here. So please stop the personal attacks.

This thread is to help the OP understand the relationship of different formats for DOF. Take an older crop camera and a newer full frame, with the same pixel density per area of sensor space, and the COC debate here is only causing OP of Confusion. :lol:

Also to address hyper focal distance.

Just because setting a lens to the minimum hyper focal distance gives acceptable results for many in terms of COC. The depth of field is still less until you hit infinity focus. I've taken over 60,000 landscape photos in the last couple of years. I speak from experience in the real world and not assumptions of acceptable COC used by depth of field calculators.

If I set my camera to minimal hyper focal distances, things like mountains and stars in the distance will be sharp enough, but not always fully sharp. If I set my camera to infinity focus, both mountains and stars are in sharp focus. That's thousands of light years in distance for the DOF. :lol:

But everything I just posted should be ignored by the OP, because it is all off topic to the question of what varies between two different formats.


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