EnCapture wrote:
So in other words, DOF is NOT affected by sensor size since the crop of an image from a FF sensor made and stretched to match that of an image from 1.6x sensor is IDENTICAL.. now stop trying to show off and impress everyone with your (referring ot more than one person) vast knowledge, stop calling folks clowns and simply accept that you are WRONG. you can twist it and talk about the effects of magnification circles of confusion and the rotational axis of Jupiter but ,unfortunately, the original poster didnt ask about these things nor their impact. take a FF image. crop it
stretch it. and you get the same image.
In what way is taking a full frame image and cropping it different to taking a shot with a cropped sensor
The size of the sensor/negative is important as it fixes the minimum amount of magnification required to produce a print of a given size. The amount of magnification effects the DOF therefore the size of the sensor effects DOF when all other factors are constant. QED.
I can't believe someone brought pixel pitch into this. So long as it's small enough, pixel pitch does not have any effect on DOF. The argument falls through if we switch to film (fully expecting someone to resort, "What's film?").
jmcfadden wrote:
(hint: that’s how you can make bigger prints with your 6 megapixel camera than you could with your old 3 megapixel camera).
John, I would submit that this particular argument is with regard to how well the printer can reproduce the part of the image that's in focus, once you specify a ppi for the print and a viewing distance etc. The number of MP (or pixel size) will no doubt influence the size at which someone might think of printing an image, so for digital and discussions of DoF, we still have to standardize the conditions if we want to establish meaningful comparisons. Once photosite (and their equivalent grain cluster) sizes are sufficently small, do we not end up with the same considerations as before to determine DoF - i.e. if the CoC is bigger than the photosites, then the photosites just record the CoC more faithfully and we'll still see it when we enlarge? The analog, errr, analogy is the development of finer and finer grained films, is it not?
What does this mean? The format size doesn't affect DOF but the camera somehow does? How do you figure? Isn't format size sort of tied to the camera?
I can pretty easily demonstrate that my digicam has more DOF than my 1Ds. The cause of this according to you, is not the format size, but some other inherant propropty of the camera? Do you mind telling me what?
Why don't you just stay out of these discussions if you don't have clue?
You might read the aforementioned article on photo.net, in particular the part about circle of confusion. The photo.net article is pretty much right on the money.
stevei wrote:
It's just so simple. If you have a different sized sensor, you WILL use a different focal length, that is a direct consequence of the different sized sensor. You cannot move yourself forwards or backwards to get the same composition, a given composition can be taken from only one point, otherwise you change the relationship between the size of different objects at different distances from the camera.
So, you have two cameras, an FF and a 1.6 crop. You stand in the same place and take the same picture. You do this with a 50mm lens on the 1.6 crop camera, and an 80mm lens on the FF camera. To get the same DoF with the FF camera as the 1.6 crop camera you need an f-stop 1.6 times greater, e.g. f/3.2 on the FF camera compared to f/2 on the 1.6 crop camera. That's all there is to it, try it out with a DoF calculator, it's simple to prove....Show more →
Exactly, thanks Steve
I think John's analysis above is incorrect in practical terms although at extreme limits it may have some validity. Example, how much DOF does a 640x480 image have if I print it 40x50? - probably none because it will look so crappy that nothing appears to be in focus. The D2X & 1Ds (and any of the orher relevant digital SLRs) are high enough resolution that for reasonable sized prints the in focus area can always appear sharp.
Lets get this straight. DOF, Depth of Field refers to the area foreward of and behind the focus point that is still in focus.
At any given distance, any given focal length and any given aperture setting the area in focus, or Depth of Field will not change by merely changing the size of the sensor.
Circles of confusion are DOF effects, that is the aesthetics of the out of focus area, outside the the area in focus. These are dependant on aperture sttings and focal length, but have little to do with the size of the sensor other then the amount of up-sizing needed to compensate for the smaller sensor. That would be percieved DOF effects. Nothing more.
In other words blowing a print up from 5x7 to 8x10 or 16x20 no more changes the actual DOF of a lens/body set-up then does the size of the sensor.
nsbca wrote:
Circles of confusion are DOF effects, that is the aesthetics of the out of focus area, outside the the area in focus. These are dependant on aperture sttings and focal length, but have little to do with the size of the sensor other then the amount of up-sizing needed to compensate for the smaller sensor. That would be percieved DOF effects. Nothing more.
In other words blowing a print up from 5x7 to 8x10 or 16x20 no more changes the actual DOF of a lens/body set-up then does the size of the sensor.
"the aesthetics of the out of focus area" - no, that's bokeh, which we covered in the previous lesson. This lesson is about DoF. The DoF is calculated from (aka defined by) the circle of confusion, not vice versa. The circle of confusion is "chosen" for a particular size print viewed at a specified distance, based on how well the human eye can, on average, perceive detail/sharpness. So if you routinely plan to print at a different size than that for which the DoF was calculated, you should recalculate the DoF scales and not use the ones on the lens. Earlier parts of the thread and the links to explanatory articles *are* worth reading!
nsbca wrote:
At any given distance, any given focal length and any given aperture setting the area in focus, or Depth of Field will not change by merely changing the size of the sensor.
Yeah, but the point is, when you change sensor size you do change focal length. I don't shoot 1.6x tighter when I shoot my 20D compared to my 1Ds. I don't shoot 5x tighter when I use my SD400. Do you?
The “Circle of Confusion” is an arbitrary factor, used as an aid in selecting an appropriate depth of field to provide subjectively “acceptable” sharpness for a desired enlargement size. It is a term that has been adopted as an attempt to describe the amount of subjective “unsharpness” that is acceptable to the human eye in a photographic print. It has ABSOLUTELY NO BEARING WHATSOEVER on the physical depth of field properties of a lens or camera format. As someone rightly pointed out, you can't change physics, even if you pretend you can by posting contrary notions on your web site.
Depth of Field is result of the eyes ability to tell when images are sharp. Take a page with hundreds of different size dots on it. Use a magnifying glass and determine that no two dots are the same size. Now view the page from a comfortable distance of say 10 inches, about 25 cm, and the eye will interpret many of the smaller dots as the same size. The minimum size that the eye can resolve is called the limit of resolution of the eye and is a result of the diffraction limitations of the eye. An average eye can resolve about .003 inches (.08 mm). In practice a more liberal limit of .01 inches (.25 mm) is used. This is the basis for all CoC numbers used in DOF calculations. A picture can be thought of as a collection of dots and if the dots appear sharp the print will appear sharp.
The advent of digital photography has not changed the human eye, it is still analog. Nor has it changed the appearance of prints, whether produced by an inkjet printer or more traditional wet methods.
nsbca wrote:
At any given distance, any given focal length and any given aperture setting the area in focus, or Depth of Field will not change by merely changing the size of the sensor.
It is true that the image falling on the sensor is the same is the same image for a given distance, FL and fstop. However, the DoF is not "embedded" in the sensor information. There is no such item as "theoretically" in focus that can be defined without referring to the human eye's capability.
If you printed, let's say a hypothetical FF 24x26mm sensor image of a landscape at 24x36mm and looked at it from 18 inches, it would likely look small but supersharp in its entirety, and appear to be all in focus. Same would likely be true for a 4x6 print. Print it at say 8x12 inches and the pebbles in the foreground would seem a little fuzzy, while the branches of the tree in the distance still looked sharp. Blow it up bigger and you will see that the flowers at the focus point in the mid ground are still sharp but both the pebbles and the branches seem less sharp. The degree to which you magnify the image has a demonstrable effect on what is perceived (only your eye/brain can do the perceiving) to be in focus.
bouch wrote:
Yeah, but the point is, when you change sensor size you do change focal length. I don't shoot 1.6x tighter when I shoot my 20D compared to my 1Ds. I don't shoot 5x tighter when I use my SD400. Do you?
The focal length of a lens is a mathamatial equation that has nothing to do with the fact that you shaved a few MM of the sides of your sensor. You are talking about adding other varialbles to the equation such as perspective and changing lenses to accommodate FoV. Yes, then things change, but you haven't changed the actual DOF of a given lens/body combination.
Wow, this thread makes my non-physics minded head spin.
OK, here's my question (probably a stupid one) and the bottom line for me. Let's say you have a basic DOF chart or tool. One that does not claim to account for crop factors or anything. And let's say you are using a 50mm lens on a 1.3 crop sensor like a 1D, and you want to determine hyperfocal distance and the min/max distances that will be in focus at a specified aperture.
Should you select 50mm from the chart to get your answers, or should you choose 65mm (50 x 1.3)?
Don't wack me too hard if this is a really stupid question.
AJSJones wrote:
It is true that the image falling on the sensor is the same is the same image for a given distance, FL and fstop. However, the DoF is not "embedded" in the sensor information. There is no such item as "theoretically" in focus that can be defined without referring to the human eye's capability.
If you printed, let's say a hypothetical FF 24x26mm sensor image of a landscape at 24x36mm and looked at it from 18 inches, it would likely look small but supersharp in its entirety, and appear to be all in focus. Same would likely be true for a 4x6 print. Print it at say 8x12 inches and the pebbles in the foreground would seem a little fuzzy, while the branches of the tree in the distance still looked sharp. Blow it up bigger and you will see that the flowers at the focus point in the mid ground are still sharp but both the pebbles and the branches seem less sharp. The degree to which you magnify the image has a demonstrable effect on what is perceived (only your eye/brain can do the perceiving) to be in focus. ...Show more →
Then by this logic I can change the DOF characteristics of my 1Ds w/85mm lens combination by simply changing the prints size of an image form 16x20 to 40x60.
That would only be the percieved characteristics, not the mathematical ones, which, by the way, do not bend just because someone needs glasses or stands 20' from the image instead of 2'.
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.
nsbca wrote:
You are talking about adding other varialbles to the equation such as perspective and changing lenses to accommodate FoV. Yes, then things change, but you haven't changed the actual DOF of a given lens/body combination.
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.
Mark Sisco wrote:
Wow, this thread makes my non-physics minded head spin.
OK, here's my question (probably a stupid one) and the bottom line for me. Let's say you have a basic DOF chart or tool. One that does not claim to account for crop factors or anything. And let's say you are using a 50mm lens on a 1.3 crop sensor like a 1D, and you want to determine hyperfocal distance and the min/max distances that will be in focus at a specified aperture.
Should you select 50mm from the chart to get your answers, or should you choose 65mm (50 x 1.3)?
Don't wack me too hard if this is a really stupid question.
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. DOF is determined by physics. not the human eye, and not anything else. going by the explanation in here, FOV is also determined by the strength of one's prescription for their glasses since what may seem in focus to one will be blurry to another (i know its a silly and extreme example but it is also very applicable)
Edited by EnCapture on Aug 12, 2005 at 11:10 PM GMT
Edited by EnCapture on Aug 16, 2005 at 06:15 AM GMT
. Actually, you should really consider the merits of non-existent cameras, lens, and printers to get to the bottom of this whole depth of field thing.