I understand what you are saying about one subject appearing to have a different DOF because it was blown up to a larger size, but actual DOF( the area in focus) is a mathematical equation that has nothing to do with print size.
I quoted the mathematical equation in my first post. The equation needs a number for CoC, which is based on the limit of resolution of the human eye. The limit of resolution of the human eye will change as the distance to the viewed print changes.
EnCapture wrote: FOCAL LENGTH DOES NOT CHANGE!!!! ONLY FIELD OF VIEW!!!! ou dont get closer to the subject, just a smaller crop of the full framed version
Edited by EnCapture on Aug 12, 2005 at 10:55 PM GMT
But, EnCapture, this simply isn't the way people use cameras. No one tends to shoot tighter the smaller their format. They shoot the same field of view but use shorter focal lenghts. Is this point lost on you, or do you simply disagree?
bouch wrote:
But, EnCapture, this simply isn't the way people use cameras. No one tends to shoot tighter the smaller their format. They shoot the same field of view but use shorter focal lenghts. Is this point lost on you, or do you simply disagree?
we arent talking about how people use a camera. the original question asked was whether frame size alters DOF (actual physical portion of the image that is in focus that is measurable). since nothing else was mentioned (such as changing lenses, circles of mass destruction or anything else) you have to assume that the original poster was asking that if under controlled conditions and only sensor size being the variable, would the DOF change. and the answer is no. just as focal length is determined only by the lens and not by crop factor etc.
Edited by EnCapture on Aug 12, 2005 at 11:15 PM GMT
Edited by EnCapture on Aug 16, 2005 at 06:15 AM GMT
bouch wrote:
Other variables to accomadate FoV? Field of view is everything here. I see you have a 1DMkII. Tell me, do you frame everything 1.3x tighter than when you used to shoot 35mm film, or do you frame everything the same but use shorter focal lengths? Can you just answer that question?
BTW, if you do frame everything the same except with shorter lenses, you'll have more DOF than full-frame.
Finally, perspective isn't part of this at all - it's only related to distance to subject - has nothing to do with focal length, field of view, format size, DOF, etc.
What has anything you have just said have to do with Depth of Field? If I am standing 20' from a 50' high white plaster wall with my 180mm 3.5 mounted on a tripod set at f/3.5 and I first attach my 1Ds to the lens and take an image. Then, leaving the lens set the way it is and the tripod in the same position, I take another image with my 1D Mark II has the DOF changed?
DOF, I will repeat, is the area in front of and behind the focus point that is in focus.
Lastly, how come DOF scales ask for focal length, f/stop setting and distance from subject to arrive at an acurate DOF. Never once in my life did I ever see a DOF scale the asked how large the intended print size is.
Hrow wrote:
What a fire storm to a simple question. I am well aware that distance and lens impact DOF but that wasn't the question. Nor was the impact of distance, lens or aperture even a consideration when the question was framed because the question was not will the need to change focal lengths to accomadate different sensor sizes to produce the same picture result in different DOF? The answer to that is obviously yes. But that wasn't the question.
The question arose from the assertion that the sensor size itself impacts DOF. To me that made no sense but I often miss things so I thought I would ask.
To the poster who asked who suggested that view camera users use F64 and swings and tilts to get acceptable DOF... there is a difference between acceptable DOF and great DOF. Why do view camera users use F64 and S/T? Because they can! When done properly and for good purpose the DOF on a view camera far exceeds anything available on a 35mm or medium format but it is not because the film size is bigger, it is because the film and/or lens plane is altered to match the subject....Show more →
I am well aware how swings and tilts work - I've been shooting Canon T/S lenses for 30 years. I would certainly consdier the Canon T/S lenses something "available in the 35mm format". I stand by my claim that view cameras would hardly be useable if they could only be stopped down to f/22 and didn't have movements.
I can't hardly believe that you can't see how format size from a practical point of view affects DOF. Camera users don't shoot the same focal length regardless of format, they shoot the same field view regardless of format.
nsbca wrote:
Lastly, how come DOF scales ask for focal length, f/stop setting and distance from subject to arrive at an acurate DOF. Never once in my life did I ever see a DOF scale the asked how large the intended print size is.
The intened print size is built into the equation. They don't ask you for it because it's assumed. The assumption is normally an 8x10 print, I believe.
Here's what Norman Koren has to say:
An object at a distance s in front of the lens is focused at a distance d behind it, according to the lens equation: 1/d = 1/f - 1/s, where f is the focal length of the lens. If the lens were perfect (no aberrations; no diffraction) a point at s would focus to an infinitesimally tiny point at d. An object at sf , in front of s, focuses at df , behind d. At the film plane d, the object would be out of focus; it would be imaged as a circle whose diameter Cf is called its circle of confusion. Likewise, an object at sr, behind s, focuses at dr, in front of d. Its circle of confusion at d has diameter Cr.
The depth of field (DOF) is the range of distances between sf and sr, (Dr + Df ), where the circles of confusion, Cf and Cr, are small enough so the image appears to be "in focus." The standard criterion for choosing C (the largest allowable value of Cf and Cr) is that on an 8x10 inch print viewed at a distance of 10 inches, the smallest distinguishable feature is (allegedly) 0.01 inch.
nsbca wrote:
If I am standing 20' from a 50' high white plaster wall with my 180mm 3.5 mounted on a tripod set at f/3.5 and I first attach my 1Ds to the lens and take an image. Then, leaving the lens set the way it is and the tripod in the same position, I take another image with my 1D Mark II has the DOF changed?
No, the DOF doesn't change, the FOV does. Is that how you normally shoot?
Lastly, how come DOF scales ask for focal length, f/stop setting and distance from subject to arrive at an acurate DOF. Never once in my life did I ever see a DOF scale the asked how large the intended print size is.
The CoC is already factored in to the equation based on the size of a standard print and standard viewing distance. Canon list the size they use on their site. Most DOF calculators allow you to pick a CoC or pick a format (which changes the CoC value).
Here is the best treatment on the web of DOF and CoC to the best of my knowledge. Van Walree covers CoC, confusion over background blur etc. His text is concise and to the point, but not brief. Anyone who really wants to argue beyond this point should start quoting scholarly text, as Van Walree does. Linking to a site is not a scholarly text. Everything I have posted in this thread I can quote numerous college texts confirming what I've written.
nsbca wrote: bouch wrote:
Is that how you normally shoot?
That is irrelevant. DOF is a mathematical equation. The way I normally shoot cannot change that.
Why irrelevant? If you wanted to shoot something with a 180 on a 1Ds, you'd change to a 140 or something on your 1D, right? You wouldn't shoot tighter, would you? So if you switched to 140 you'd end up with more DOF, right? And what forced you to switch to 140? The format size.
Bob Atkins doesn't seem to think DOF can be pinned so precisely. From the before referenced photo.net article:
First, DOF relates to a print or other reproduction of an image. It's NOT an intrinsic property of a lens. If you put a lens on an optical bench you can measure focal length, you can measure aperture, but you can't measure depth of field. Depth of field depends on some subjective factors which I'll discuss later.
f I am standing 20' from a 50' high white plaster wall with my 180mm 3.5 mounted on a tripod set at f/3.5 and I first attach my 1Ds to the lens and take an image. Then, leaving the lens set the way it is and the tripod in the same position, I take another image with my 1D Mark II has the DOF changed?
How can the DOF change? The image has no foreground and no background. Your example is irrelevant to a discussion of DOF.
The way folks stated it, the FF would provide more shallow depth of field - period. All I know is that the DOF/Bokeh/background blur of images shot with my 20D and 85L at f/1.2 appear just as shallow and dreamy as those that I see here shot by others with FF cameras at f/1.2.
Now if we were shooting the same subject and I had to move in closer to the subject to get the same framed shot with the FF that I had taken with the 1.6 crop 20D, then of course I would expect that the closer distance tothe subject would cause the image to have shallower DOF. Anyone who has shot macro knows about hyper shallow DOF due to close proximity.
Edited by Phil Bonner on Aug 12, 2005 at 08:59 PM GMT
Jeff Donald wrote:
Here is the best treatment on the web of DOF and CoC to the best of my knowledge.
Good link, Jeff. The example Grommit photos at f/22 are interesting - really shows how DOF is an inexact science. The background car at f/22 & 28mm is as blurry as in the 100mm photo but is part of the DOF because it's small enough that it looks acceptably sharp.
DOF is not Bokeh and it is not background blur. This is covered at Van Walree's site. Please take a few moments and read the link I've provided so that you may contribute to this thread in a meaningful way.
Van Walree has several notable quote that you would do well to learn.
"Neither the absolute nor the relative background blur should be used as a criterion to judge the depth of field. It is a common mistake to associate telephoto lenses with a shallow DOF because of the large absolute blur."
"However, in a more general comparison of two different photographs one needs to be very careful not to base a DOF judgement on the observed background blur."
EnCapture wrote:
DOF is determined by physics. not the human eye, and not anything else.
It is determined by physics, but I suggest you take a closer look at the mathematical equation. You'll find that the equation has a CoC component, the value of which is determined by the human eye!
nsbca wrote:
If I am standing 20' from a 50' high white plaster wall with my 180mm 3.5 mounted on a tripod set at f/3.5 and I first attach my 1Ds to the lens and take an image. Then, leaving the lens set the way it is and the tripod in the same position, I take another image with my 1D Mark II has the DOF changed?
If you print both images at the same size, yes, the DOF will have changed, although with a flat wall, it's not likely you'll notice any difference.
nsbca wrote:
Lastly, how come DOF scales ask for focal length, f/stop setting and distance from subject to arrive at an acurate DOF. Never once in my life did I ever see a DOF scale the asked how large the intended print size is.
The DOF scales are set according to the CoC chosen by the manufacturer. There are an infinite combination of print size and viewing distance combinations that correspond to this CoC. Canon uses a CoC of .035mm for full-frame 35mm and .020 mm for 1.6x crop factor cameras.
