Luminous Landscape Forum
Site & Board Matters => About This Site => Topic started by: NikosR on October 25, 2006, 12:54:00 am
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This is a comment on the article 'Focusing in the Digital Era - Part I' recently published on the LL site.
I am not going to argue here about the details and findings in the article. What I want to comment on is the author's basic premise that in the case of digital capture, degree of enlargement, defined as the percentage of increase of the sensor dimensions to produce a specific sized print, is of relevance. Assuming this premise results, for example, in the reasoning that an image captured by a (theoretically perfect) sensor smaller but of equal MP number than a larger (theoretically perfect) sensor can 'support' less 'enlargement', just because of its smaller geometric dimensions.
I find it hard to agree with this assertion, although it is a very common one in digital photography fora. A digital image, I believe, is a 'virtual' entity. It does not have dimensions per se, the way a piece of film has. By the time it is captured it exists in storage and it is independent of the geometric dimensions of the capture sensor. I can see no way of attributing absolute geometric dimensions to this image which are then somehow 'enlarged' to produce a print.
'Enlargement' and 'enlargeability' in the digital era depends on MP content, information amount so to speak. The degree of enlargeability is directly related to the amount of information contained and not on any non-existent geometric dimensions of the captured image.
So, can't we draw a parallel between digital and analogue capture with regards to 'enlargeability'? I believe we can but we have to go one level up in the film case to draw parallels. Examine why is that a larger piece of film can support more enlargement than a smaller one.
Information content as a measure of enlargeability is true for the film case as well. But in that case, assuming the use of the same film emulsion with a set ability for information capture per unit of area, a larger piece of film directly means more information storage capability.
Surely there are quantities directly related to the geometric dimensions and MP number of a capture sensor that will affect the DoF (Circle of Confusion), pixel pitch for one, but the author seems to ignore these. In fact, I have yet to see a conscise and convincing essay on the net dealing with the definition of the, largely subjective, CoC using terms applicable to the digital era.
I suppose this is a difference in semantics but a very important one I believe.
I would welcome constructive arguments for or against my premise.
Nikos Razis
Athens, Greece
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Ferguson's analysis is very interesting, and a pleasure to read, but it shows an obvious thing: the focus plane is just a plane, not a gross wall.
The 135 marks show the limits for perceived sharpness in the print, and this depends on the print size (8'x12' was assumed). 100% crops can not show this. The sharpest crop and the blurrest crop will not be so different in the print if it is sufficiently small. Of course, they are different, but the human eye cannot perceive the difference. This is the key point.
However, 100% crops show the differences that we cannot see on paper. The same was the case with film. There is nothing special about digital cameras here.
Ferguson explains, and this is true, that in the digital era we tend to make bigger prints. He is also right in pointing to the outdated conventions of the 30s for the circle of confusion. Actually we know that the human eye can perceive details much smaller than 30 microns.
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Ferguson's analysis is very interesting, and a pleasure to read, but it shows an obvious thing: the focus plane is just a plane, not a gross wall.
The 135 marks show the limits for perceived sharpness in the print, and this depends on the print size. 100% crops can not show this. The sharpest crop and the blurest crop will not be so different in the print if it is sufficiently small. Of course, they are different, but the human eye cannot perceive the difference. This is the key point.
However, 100% crops show the differences that we cannot see on paper. The same was the case with film. There is nothing special about digital cameras here.
Ferguson explains, and this is true, that in the digital era we tend to make bigger prints. He is also right in pointing to the outdated conventions of the 30s for the circle of confusion. Actually we know that the human eye can perceive details much smaller than 30 microns.
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The author is right in many things he says in the article. He is also quite accurate in many of his subjective comments. My problem is his attempt at a theoretical substantiation of his observations.
I made the original post just to pin-point an incorrect in my opinion assertion about 'enlargeability' that is made in the beginning of the article, and repeated unsubstantiated in other places in the text.
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I think one of the main points that Gary is trying to make is that unless we are careful about how we focus, then the bottleneck on image quality will be the limited depth of field imparted by the lens. It doesn't matter how many pixels the sensor has. Imagine using a 50 mm lens on a camera. No matter what kind of sensor the camera has or how many pixels it has, the lens will form (i.e., project) the same image onto the sensor plane (i.e., the imaging plane). The projected image depends only on the optics of the lens, how the lens is focused, and the laws of physics, nothing else.
Suppose there is a blurry spot in the resulting image that measures 2 mm by 2 mm. It doesn't matter whether this spot is digitized by the sensor using 50 pixels or 5000 pixels. The total amount of "image information" within that 2x2 mm area is constant. If that 2x2 mm area is enlarged in a print to be 20x20 mm, it will look equally blurry in either case.
To carry this example one step further: the only way in which 5000 pixels will be more useful than 50 pixels is if that "blurry spot" described above is actually sharp enough so that 5000 pixels can pick up detail that 50 pixels cannot. (In semi-math speak, the frequency content of that area has to be sufficiently high, otherwise adding more samples is useless.) And the only way the blurry spot can be "sharp enough" is by making sure that the area lies enough within the depth of field.
Eric
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I think one of the main points that Gary is trying to make is that unless we are careful about how we focus, then the bottleneck on image quality will be the limited depth of field imparted by the lens. It doesn't matter how many pixels the sensor has. Imagine using a 50 mm lens on a camera. No matter what kind of sensor the camera has or how many pixels it has, the lens will form (i.e., project) the same image onto the sensor plane (i.e., the imaging plane). The projected image depends only on the optics of the lens, how the lens is focused, and the laws of physics, nothing else.
Suppose there is a blurry spot in the resulting image that measures 2 mm by 2 mm. It doesn't matter whether this spot is digitized by the sensor using 50 pixels or 5000 pixels. The total amount of "image information" within that 2x2 mm area is constant. If that 2x2 mm area is enlarged in a print to be 20x20 mm, it will look equally blurry in either case.
To carry this example one step further: the only way in which 5000 pixels will be more useful than 50 pixels is if that "blurry spot" described above is actually sharp enough so that 5000 pixels can pick up detail that 50 pixels cannot. (In semi-math speak, the frequency content of that area has to be sufficiently high, otherwise adding more samples is useless.) And the only way the blurry spot can be "sharp enough" is by making sure that the area lies enough within the depth of field.
Eric
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Most of what you're saying seem true to me. Information content is only useful data and a blurry patch will be blurry regardless with how many pixels it is digitized.
However, where is the direct connection between sensor dimensions and what you are describing? Why would a larger sized sensor be any different? (leaving lens resolution and diffraction issues aside).
The only connection I can establish is, as I hinted in my OP, pixel pitch.
Remember, my gripe wih regards to the article is the explicit and implied direct connection between sensor size and ability to enlarge. Not wanting to tread onto the treacherous path of CoC determination and DoF calculation for digital capture, I would believe that a smaller sized sensor (hence with higher pixel pitch) would provide deeper DoF than a larger one of the same Mp count. Not the other way around as the article seems to imply.
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I found the article rather convenient & straightforward, although not entirely comprehensive. Waiting for the PART II, PART III.
Regards
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Most of what you're saying seem true to me. Information content is only useful data and a blurry patch will be blurry regardless with how many pixels it is digitized.
However, where is the direct connection between sensor dimensions and what you are describing? Why would a larger sized sensor be any different? (leaving lens resolution and diffraction issues aside).
The only connection I can establish is, as I hinted in my OP, pixel pitch.
Remember, my gripe wih regards to the article is the explicit and implied direct connection between sensor size and ability to enlarge. Not wanting to tread onto the treacherous path of CoC determination and DoF calculation for digital capture, I would believe that a smaller sized sensor (hence with higher pixel pitch) would provide deeper DoF than a larger one of the same Mp count. Not the other way around as the article seems to imply.
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There is no need to deal with the complexities of CoC and DoF calculations since these caclulations can be done by online calculators such as the one on Cambridge in Color:
[a href=\"http://www.cambridgeincolour.com/tutorials/DOF-calculator.htm]http://www.cambridgeincolour.com/tutorials...-calculator.htm[/url]
If you plug in the variables for a 35 mm full frame with a 50mm lens and 6 by 7 cm with an 80 mm lens, you will see that the smaller format has a greater depth of field.
The resolution of the sensor does not enter directly into the calculation, but if the increased details associated with great depth of field can not be resolved by the sensor, the full depth of field can not be utilized.
Bill
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There is no need to deal with the complexities of CoC and DoF calculations since these caclulations can be done by online calculators such as the one on Cambridge in Color:
http://www.cambridgeincolour.com/tutorials...-calculator.htm (http://www.cambridgeincolour.com/tutorials/DOF-calculator.htm)
If you plug in the variables for a 35 mm full frame with a 50mm lens and 6 by 7 cm with an 80 mm lens, you will see that the smaller format has a greater depth of field.
The resolution of the sensor does not enter directly into the calculation, but if the increased details associated with great depth of field can not be resolved by the sensor, the full depth of field can not be utilized.
Bill
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I'd rather limit the discussion of DoF for digital sensors, since I believe it is a bit off-topic in this thread (with regards to my OP) and is a thorny issue IMO.
However, since you mention it, have you wondered how the author of that particular calculator has determined the CoC for the various digital sensors? I have seen no conscise treatment for CoC determination for digital sensors.
The author of the DoF calculator does not treat digital and film any differently, quoting the sensor dimensions enlargement required to bring it up to 8x10 as the way to determine the CoC to be used. But this assertion that a digital image is enlarged from the sensor size to the final print is what I'm arguing against.
Just to put it another way, although I suspect this statement will not go down well with many: It is my assertion that an APS-C sized, for example, sensor of 3Mp has a very different CoC, and hence DoF, than an APS-C sized sensor of 12Mp. This might sound strange at first thought, but think about it a little in terms of apparent sharpness of a print produced at a certain size.
In fact, your statement in your last sentence, supports well what I'm suggesting. I suggest the same thing, but without having to resort to notions of 'depth of field utilization'.
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My take-away from the article is that one should focus carefully. Is this a revelation? The biggest practical change between the film and digital era is this regard is that it is easier and cheaper to make larger prints and so the results may come under greater scrutiny ("stop that fellow with the loupe!"). On the other side, there are digital tools that aid upscaling.
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In fact, I have yet to see a conscise and convincing essay on the net dealing with the definition of the, largely subjective, CoC using terms applicable to the digital era.
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I think that is because "DOF doesn't care about the recording media type or size ... ."
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I think that is because "DOF doesn't care about the recording media type or size ... ."
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I beg to differ. These notions are inherent in the traditional calculations for DoF. The related parameter is the CoC which, while subjective to a large extent, has always been defined by convention in terms of film capture area and output size.
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If fact, DoF depends on media size. It depends on the Circle of Confusion. The Circle of Confusion depends on the resolutive capacity of the observer's eyes, the film or sensor size and the print size.
DoF depends on other variables as well, like focal lengh, aperture, distance to the subject and hyperfocal distance.
http://en.wikipedia.org/wiki/Depth_of_fiel...f_field_formula (http://en.wikipedia.org/wiki/Depth_of_field#Depth_of_field_formula)
Digital cameras are under the same rules. The only difference is a constrain related to minimum CoC and pixel size.
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If fact, DoF depends on media size. It depends on the Circle of Confusion. The Circle of Confusion depends on the resolutive capacity of the observer's eyes, the film or sensor size and the print size.
As I have already exlained, I fail to see the direct relationship between sensor size and CoC. Asserting that a direct relationship exists (similar to the film case) would entail that one accepts the concept of 'enlarging' the sensor dimensions to the final output to be judged (say 8x10).
As I've repeatedly said, I fail to see this direct relationship in the case of digital capture, reason being the sensor is never enlarged. It just produces a digital representation of the image with only Mp resolution and as its 'native dimension'.
DoF equations, and in particular the conventions regarding the CoC need to be changed or updated to properly account for digital capture.
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As I've repeatedly said, I fail to see this direct relationship in the case of digital capture, reason being the sensor is never enlarged. It just produces a digital representation of the image with only Mp resolution and as its 'native dimension'.
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Perhaps you fail to see a relationship because none exists. Circle of confusion is an optical term with nothing to with cameras (digital or otherwise). It merely has to do with the optical fact that an out of focus point of light will form a circle.
I suggest some folks read more carefully Michael Reichmann's article on this site about "Understanding Depth of Field."
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This article kind of mystifies me. I haven't seen the "problem" that the author describes. I regularly make 16x20 prints from 1Ds captures (not Mk II) which exhibit excellent front-to-back sharpness from a few feet to infinity. This is one of the big reasons I went digital--the potential for greater enlargeability (with acceptable sharpness) compared to film.
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Perhaps you fail to see a relationship because none exists. Circle of confusion is an optical term with nothing to with cameras (digital or otherwise). It merely has to do with the optical fact that an out of focus point of light will form a circle.
I suggest some folks read more carefully Michael Reichmann's article on this site about "Understanding Depth of Field."
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What is used in the DoF calculations is the CoC Limit (simplistically called the CoC) which has everything to do with cameras. It is a somewhat arbirtary choice for the limit of acceptable sharpness based on conventions. Perhaps you are not aware of the commonly used (and rightly disputed in the article) conventions behind the CoC Limit choice for different film sizes?
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What is used in the DoF calculations is the CoC Limit (simplistically called the CoC) which has everything to do with cameras. It is a somewhat arbirtary choice for the limit of acceptable sharpness based on conventions. Perhaps you are not aware of the commonly used (and rightly disputed in the article) conventions behind the CoC Limit choice for different film sizes?
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I am quite aware of the optical equations and how to apply them to photography. "Acceptable sharpness" need not be based on any convention. It can be personal. I belive it is a personal thing and don't want it decided for me by Canon, Mamiya, Zeiss, etc.. There is no need to allow anyone else to decide what is sharp for you, unless you don't want to be bothred with that decision.
CoC Limit may have everything to do with a camera, but CoC is a "print" term. How does a painter make something appear out of focus? What about slides or computer screens? Circle of confusion (defined and used well before cameras came along) is an optics term. Now, the circle of confusion may pass through a camera on its way from scene to screen, but ceratinly has nothing to do with the kind (digital or film) or format (call it sensor size) of the camera.
There are many self described "experts" on DoF, but they refuse to (or can't) answer the question about which term(s) in the optical equations are "format." Some might even try to tell you optics equations don't work for photography.
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I am quite aware of the optical equations and how to apply them to photography. "Acceptable sharpness" need not be based on any convention. It can be personal. I belive it is a personal thing and don't want it decided for me by Canon, Mamiya, Zeiss, etc.. There is no need to allow anyone else to decide what is sharp for you, unless you don't want to be bothred with that decision.
CoC Limit may have everything to do with a camera, but CoC is a "print" term. How does a painter make something appear out of focus? What about slides or computer screens? Circle of confusion (defined and used well before cameras came along) is an optics term. Now, the circle of confusion may pass through a camera on its way from scene to screen, but ceratinly has nothing to do with the kind (digital or film) or format (call it sensor size) of the camera.
There are many self described "experts" on DoF, but they refuse to (or can't) answer the question about which term(s) in the optical equations are "format." Some might even try to tell you optics equations don't work for photography.
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I won't disagree with you. I will just note that subscribing to your point of view does away with any notion of 'calculating' DoF which is fine by me. Perhaps you should convince the article author though
Not calculating DoF is fine by me. It IS after all a subjective issue. But if you want to calculate it (or approximate it mathematically) you have to put in this silly little parameter of CoC Limit which in film is size dependent amongst other things. You can't have it both ways.Unless you can propose an alternative approach towards calculating it.
I really did not want to start all this DoF discussion, which as I said is quite off-topic but I was dragged in it. It has been beaten to death many times to no avail.
Now its your turn. Do you agree or disagree with my original post about sensor size not being enlarged in any way to produce the final output, thus sensor size is in this respect not directly influencing 'enlargeability'. This was my original assertion and my main disagreement with the article in reference. (I hope you have read both). I just hate it when discussions get side-tracked.
(BTW, there are other things that bother me in the referenced article. Like the fact that the author is using 100% crops to 'prove' that the engraved DoF zone is not good enough to provide resuts indistinguishable from when the subject is properly focused. This is quite silly IMO since he only 'proves' the obvious. He would get the same results just by examining a piece of film under a loupe, or printing a print large enough to test the sensor used. The author ignores what should be obvious. That DOF scales, even when applied to the format they were calculated for, provide for 'acceptable' sharpness for a specific defined output size. 8x10 usually viewed from a specific distance. Nothing more than that. So he proves nothing we didn't know already).
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I won't disagree with you. I will just note that subscribing to your point of view does away with any notion of 'calculating' DoF which is fine by me. Perhaps you should convince the article author though.
Now its your turn. Do you agree or disagree with my original post about sensor size not being enlarged in any way to produce the final output, thus sensor size is in this respect not directly influencing 'enlargeability'. This was my original assertion and my main disagreement with the article in reference. (I hope you have read both). I just hate it when discussions get side-tracked.
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I don't know where you got the idea I was saying one cannot calcualte DoF. I do it frequently when designing a print. I was just saying the print designer does not need to have his lens/camera maker tell him what convention he should be using. Sure, I use the convention that the average person can detect about 1 minute of angle. I am not "stuck" with that though. When I make prints for my eagle-eyed son, I close that down a bit.
Yes, I agree completely sensor size has nothing to do with calculating DoF. I have yet to be required to use camera format to determine DoF.
I will not post any further comments so as to do my part to end this DoF discussion.
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Nikos, DoF calculations for a digital sensor are not particularly different from DoF calculations for film. In both cases, as Howie likes to emphasize, DoF is a property of the optics and not the sensor (provided the sensor has enough pixels or fine enough grain to resolve the optical circle of confusion). As you guessed, the pixel pitch provides the connection between pixels and distance for the digital sensor.
If you want equations:
CoC (print) = CoC (sensor) x Magnification
CoC (print) is the blur size on the final print. The largest acceptable CoC is determined by factors like print size, viewing distance, and visual acuity.
CoC (sensor) is the blur size on the sensor. This is determined by optical factors like distance to subject, lens focal length, and lens aperture of f/stop.
Magnification is the degree of enlargement needed to go from sensor to print. What does magnification mean for digital sensors? Let's assume one pixel on the sensor is printed as one dot on the print. (If the digital file is resized upwards or downwards before printing, you can include this as an extra magnification factor, but I will ignore it here.) Magnification is then the ratio of the print size to the sensor size, which is also the ratio of the size of a dot on the print to the size of a pixel on the sensor. An example will probably make this clearer than words.
Example:
8 inch print at 300 dots/inch from
2400 pixels on sensor with 8 micron pixel pitch
Here are two equivalent ways to calculate magnification:
Magnification = print size / sensor size
= (8 inch) / (2400 x 8 micron) ~ (200mm) / (19.2mm) ~ 10
Magnification = print dot size / sensor pixel size
= (1/300 inch) / (8 micron) ~ (85 micron) / (8 micron) ~ 10
Why does the physical size of the pixel matter, not just the pixel count of the digital file? It comes back to the point that the CoC on the sensor is a physical quantity, with actual dimensions in microns not pixels.
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Nikos, DoF calculations for a digital sensor are not particularly different from DoF calculations for film. In both cases, as Howie likes to emphasize, DoF is a property of the optics and not the sensor (provided the sensor has enough pixels or fine enough grain to resolve the optical circle of confusion). As you guessed, the pixel pitch provides the connection between pixels and distance for the digital sensor.
If you want equations:
CoC (print) = CoC (sensor) x Magnification
CoC (print) is the blur size on the final print. The largest acceptable CoC is determined by factors like print size, viewing distance, and visual acuity.
CoC (sensor) is the blur size on the sensor. This is determined by optical factors like distance to subject, lens focal length, and lens aperture of f/stop.
Magnification is the degree of enlargement needed to go from sensor to print. What does magnification mean for digital sensors? Let's assume one pixel on the sensor is printed as one dot on the print. (If the digital file is resized upwards or downwards before printing, you can include this as an extra magnification factor, but I will ignore it here.) Magnification is then the ratio of the print size to the sensor size, which is also the ratio of the size of a dot on the print to the size of a pixel on the sensor. An example will probably make this clearer than words.
Example:
8 inch print at 300 dots/inch from
2400 pixels on sensor with 8 micron pixel pitch
Here are two equivalent ways to calculate magnification:
Magnification = print size / sensor size
= (8 inch) / (2400 x 8 micron) ~ (200mm) / (19.2mm) ~ 10
Magnification = print dot size / sensor pixel size
= (1/300 inch) / (8 micron) ~ (85 micron) / (8 micron) ~ 10
Why does the physical size of the pixel matter, not just the pixel count of the digital file? It comes back to the point that the CoC on the sensor is a physical quantity, with actual dimensions in microns not pixels.
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Thank you Eric. You expressed quite succintly the fact that its pixel no AND pixel pitch that should determine the CoC in digital.
In film of course, assuming same emulsion, 'pixel pitch' so to speak is constant, thus we only have the size (= 'pixel no') to play with.
All this of course does not bode well with the article's in question assertion that smaller sensors support 'less enlargement' which was my original complaint.
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So what I said in a previous post about same sized but different Mp Number sensors having different CoC seems to be indeed true. This fact is not reflected in any DoF calculator that I know of.
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Hmm, sounds like there is still some confusion .... let me try again.
The CoC on the sensor is determined by the optics, not the sensor. Two different sensors, with different pixel pitch (same physical size but different pixel count), will have the same CoC, expressed in physical units like microns, if the same optics are used to form the image. This is intuitive for film cameras (film granularity has nothing to do with CoC) and the same principle applies for digital cameras (pixel density has nothing to do with CoC).
Of course if you measure the CoC in pixels instead of microns, then pixel pitch enters the equation. But this is a backwards way of thinking, sort of like a film photographer thinking "my film has a grain size of 8 microns and my image occupies 2400 grains of film" rather than "my image occupies 19mm of film". When calculating CoC, the second way of thinking seems simpler, and it emphasizes that pixel pitch or film grain is irrelevant.
DoF calculators require the user to enter phisical quantities like image size. Given just the pixel count of a digital file (like 6MB = 2000x3000 pixels) and no information on physical image size or pixel pitch, there is not enough information for the calculation. The DoF calculator can calculate how large a CoC is formed by a particular lens, but has no way of translating this into pixels without knowing the phisical pixel size or sensor size.
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While I agree with the basic principle of the article, I think this issue is over-exaggerated. First, with digital landscapes and "front to back" DOF I don't usually have a problem when printing at A3 and don't find the issue much different than film days. Second, I would dispute the fact that typical viewing size was 4x6 in film days. Maybe for snapshot drugstore prints, but serious amateurs like myself and even my dad typically printed 8x10 or larger, and in fact in my family the habit was to shoot chrome and project viewing at 40 inches. Bottom line - I don't really see where digital has significantly changed DOF issues from film days except possibly for those who never used to print larger than snapshot (4x6) size.
- DL
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As I have already exlained, I fail to see the direct relationship between sensor size and CoC. Asserting that a direct relationship exists (similar to the film case) would entail that one accepts the concept of 'enlarging' the sensor dimensions to the final output to be judged (say 8x10).
Well, it is easy to see. The sensor reproduces some real detail. Lets say, a branch in a distant tree. It is reproduced in a 24x36 surface. That miniaturized reproduction of the branch must be reproduced in the print. If you want a 8x12 print you need to enlarge that reproduction of the branch 8,5 times. It has nothing to do with number of pixels. You have the same number of pixels in a A4 or A3 print, like you had the same number of grains "projected" from the film to the paper. They point is you have a reproduction, an image, projected by the lens on the focal plane (the branch of the tree). That image is capture by something (it doesn't matter if film or sensor), but the image that the lens draws has physical dimensions, and it must be enlarged. The branch or the face of a person, including all the details captured, are multiplied by 8,5 times for a 8x12 (A4) print.
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Hmm, sounds like there is still some confusion .... let me try again.
The CoC on the sensor is determined by the optics, not the sensor. Two different sensors, with different pixel pitch (same physical size but different pixel count), will have the same CoC, expressed in physical units like microns, if the same optics are used to form the image. This is intuitive for film cameras (film granularity has nothing to do with CoC) and the same principle applies for digital cameras (pixel density has nothing to do with CoC).
Well, this is were I tend to disagree. I can see the CoC being independent of the medium's resolution, but not the CoC diameter limit that is used in DoF calculations. And so do lots of other people like Norman Koren. But, it is too late over here for me to think harder and I'm off to bed.
Another DoF discussion was not what I had in mind with my original post.
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Well, it is easy to see. The sensor reproduces some real detail. Lets say, a branch in a distant tree. It is reproduced in a 24x36 surface. That miniaturized reproduction of the branch must be reproduced in the print. If you want a 8x12 print you need to enlarge that reproduction of the branch 8,5 times. It has nothing to do with number of pixels. You have the same number of pixels in a A4 or A3 print, like you had the same number of grains "projected" from the film to the paper. They point is you have a reproduction, an image, projected by the lens on the focal plane (the branch of the tree). That image is capture by something (it doesn't matter if film or sensor), but the image that the lens draws has physical dimensions, and it must be enlarged. The branch or the face of a person, including all the details captured, are multiplied by 8,5 times for a 8x12 (A4) print.
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A larger sensor with less Mp according to your assertion will have to be 'enlarged' less but will it produce a better enlargement than a smaller sensor with more Mps?
Even more importantly, a larger sensor with the same no. of Mp as a smaller sensor will produce a better print because the degree of 'enlargement' is less? (Noise and such issues not withstanding)
I just find it hard to buy this.
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8,5 is the ratio of the diagonals of the 24x36mm frame and the 8x12 paper. Whether you want a bigger print, you can enlarge the "projected" image (by the lens) as much as you want. The image projected by the lens has a particular physical size, limited by the circle of light. Enlarging that image (capture by any medium) you distribute the capture details in a bigger surface.
The human eyer does not resolve much detail. Therefore, things that the eye cannot distinguish when printed at small sizes, are easily distinguishable when printed at bigger sizes.
The focus plane is just a plane. Anything outside that plane is out of focus. But cannot see this if the print is small enough.
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More pixels allows for more detail to be captured from the lens, and this allows for better quality (enlarged) pictures, but it does not affect the enlargement phenomenon. Any detail the camera has captured is preserved when transferred to paper, but depending on the size of the paper that detail is spread more or less. If you spread the details too much, the human eye will see the errors, differences in focus, etc. That is the point.
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That depth of field markings (and hence CoC targets) for film aren't applicable to new sensor sizes/densities and the required degree of enlargement is obvious ... the same way that (arbitrary) CoC targets were different for different film sizes.
A better reference for all this is here:
http://www.cambridgeincolour.com/tutorials...photography.htm (http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm)
(These Cambridge in Colour articles are excellent.) If you skip down to the Diffraction Limit Calculator halfway down the page, you can calculate both the CoC and Airy Disc for a given print resolution (dimensions, viewing distance and eyesight), sensor (dimensions, megapixels) and aperture. All this is geometry. When reproducing 3D subjects, the CoC is generally the overriding determinant for "resolution" in the print ... unless it's exceeded by the pixel size or diffraction. Note the diminishing return for greater pixel densities in real world situations where the pixel size is dwarfed by CoC/diffraction (optics).
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Is it me or are the 100% crops of the house labelled wrongly? Surely the OOF one should be Infinity @ f/2.8, and not f/8.
To those who don't see the problem, are you using hyperfocal caculations for working out DOF, or are you just shooting @ f/16 anyway? What size are you enlarging to? If you're not using hyperfocal calculations, or making massive enlargements - it's all moot.
The article makes sense to me, and I think it raises a valid point - the crops illustrate his point nicely IMO.
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Is it me or are the 100% crops of the house labelled wrongly? Surely the OOF one should be Infinity @ f/2.8, and not f/8.
To those who don't see the problem, are you using hyperfocal caculations for working out DOF, or are you just shooting @ f/16 anyway? What size are you enlarging to? If you're not using hyperfocal calculations, or making massive enlargements - it's all moot.
The article makes sense to me, and I think it raises a valid point - the crops illustrate his point nicely IMO.
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Is it me or are the 100% crops of the house labelled wrongly? Surely the OOF one should be Infinity @ f/2.8, and not f/8.
To those who don't see the problem, are you using hyperfocal caculations for working out DOF, or are you just shooting @ f/16 anyway? What size are you enlarging to? If you're not using hyperfocal calculations, or making massive enlargements - it's all moot.
The article makes sense to me, and I think it raises a valid point - the crops illustrate his point nicely IMO.
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Oops, a little fat-fingering there.
The point I was trying to make before is that I haven't changed my approach to focusing at all since going digital, and it still "works", whether I'm going hyperfocal or not. I'm able to enlarge more because of the absence of film grain, but I haven't found DOF issues to be a limiting factor. For me (and my 1Ds) this just hasn't been an issue. Perhaps it's an issue with MF but not 35mm digital?
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Is it me or are the 100% crops of the house labelled wrongly? Surely the OOF one should be Infinity @ f/2.8, and not f/8.
Read the text again carefully. The shots were all taken at f/8; only focus was varied. The image labeled f/8 was taken at the closest focus setting.
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More pixels allows for more detail to be captured from the lens, and this allows for better quality (enlarged) pictures, but it does not affect the enlargement phenomenon. Any detail the camera has captured is preserved when transferred to paper, but depending on the size of the paper that detail is spread more or less. If you spread the details too much, the human eye will see the errors, differences in focus, etc. That is the point.
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I'm sorry. It sounds like you're contradicting yourself (better quality (enlarged) pictures but it does not affect the enlagement phenomenon).
Seems to me you're speaking in analog terms about a digital issue. The details are spread, yes, but only based on the Mp resolution and not based on any sensor dimension magnification.
It is like saying that a larger (physically) CD will provide more sound resolution and detail....
If what you're saying is true then the APS vs FF debate would not exist since it would be obvious that larger sensor = better quality (and not because of noise issues etc). Of course, there is a limit in pixel density from an optical point of view and this has to do with lens resolution and diffraction. But this is another story).
I can't follow your thinking. Is it just me who thinks that 'enlargement' in the digital world is not directly related with sensor size because the captured image does not have physical dimensions?
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While I agree with the basic principle of the article, I think this issue is over-exaggerated. First, with digital landscapes and "front to back" DOF I don't usually have a problem when printing at A3 and don't find the issue much different than film days. Second, I would dispute the fact that typical viewing size was 4x6 in film days. Maybe for snapshot drugstore prints, but serious amateurs like myself and even my dad typically printed 8x10 or larger, and in fact in my family the habit was to shoot chrome and project viewing at 40 inches. Bottom line - I don't really see where digital has significantly changed DOF issues from film days except possibly for those who never used to print larger than snapshot (4x6) size.
- DL
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Precisely Don!
The effects of Viewing Distance, Enlargement Factor and CoC on DoF has not changed at all with the introduction of digital. What has changed is our ability to easily discern the differences that were always there; we now have "actual pixel" view with a simple mouse-click. In film days, that level of inspection required viewing negatives through a medium-power microscope...
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The article ended with:
"Today’s big print culture means acceptable depth of field has shrunk dramatically. The old notions about hyperfocal focusing and depth of field scales based on a thirty micron circle of confusion, are redundant if you’re aiming at high quality A3 or larger prints"
The DoF scales based on 30 microns are not redundant, they are not applicable to very large or A3 prints. Maybe the problem isn't that sience has changed, but the need to be more precise and accurate in its application has changed. DoF scales are based on a standard print size viewed at a standard distance. I don't recall A3 being one of those standard sizes.
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The article ended with:
"Today’s big print culture means acceptable depth of field has shrunk dramatically. The old notions about hyperfocal focusing and depth of field scales based on a thirty micron circle of confusion, are redundant if you’re aiming at high quality A3 or larger prints"
The DoF scales based on 30 microns are not redundant, they are not applicable to very large or A3 prints. Maybe the problem isn't that sience has changed, but the need to be more precise and accurate in its application has changed. DoF scales are based on a standard print size viewed at a standard distance. I don't recall A3 being one of those standard sizes.
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Hi folks
I think that there is a lot of confusion going down - or at least, I'm getting more confused than ever. As I understrand it, this is totally an optics consideration based on the fact that all lenses of all focal length give exactly the same depth of field when used at the same aperture and with the same subject magnification. To illustrate this: if you focus a 135mm lens on a 35mm format camera at, say, five feet, you will get a pretty large head-shot. Now, using shorter or longer lenses at the same aperture to get a similarly sized image will still give you the same depth of field, only the area of background or foreground will have changed.
In 35mm format terms that 135mm lens is starting to be longish: in 4x5 format terms it is a short normal.
Printing that head shot from either format to whatever common size of head will not show a difference in depth of field, only in extra picture areas covered or lost.
N'est ce pas?
Ciao - Rob C
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Of course, there is a limit in pixel density from an optical point of view and this has to do with lens resolution and diffraction. But this is another story).
... and with the wavelengths of visible light.
Darn physics, always getting in the way!
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historic concepts of depth of field are inappropriate if enlarging to the capacity of today’s inkjet printers
It is due to two factors:
1) DoF marks are designed for A4 prints (aprox) and many of us make A3 prints.
2) Digital sensors are smaller than 35mm frames (in general).
That is all.
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It is due to two factors:
1) DoF marks are designed for A4 prints (aprox) and many of us make A3 prints.
2) Digital sensors are smaller than 35mm frames (in general).
That is all.
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Interestingly these two factors are offsetting somewhat minimizing the original point of the article. This is particularly true for P/S digital whose users are more likely the former 4x6 printers.
- DL