steve_t wrote:
If you have, say, a 1.6 crop camera then you need to understand how DOF works with your lenses on that body,
And if you print and view your pictures as assumed for the format the DoF scales were calculated for (e.g. 8x10 at a foot), you'll find the scales don't work right.
but you can't control the size of your sensor and there's no point worrying about comparative DOF with two completely differently framed shots.
Not sure anyone ever worried about that
You do however need to know that the larger you make a print the narrower DOF appears when viewed from a fixed distance, and that cropping an image and printing the cropped section out has a similar effect to making a large print.
I wish you could get imagemaster, encapture and nsbca to understand that part
How many people do you think look at photograph and say, "I wonder what sensor size he used to get that DOF."?
The same number of people that have a limited knowledge of Depth of Field and all it's applied factors. The concepts of DOF and CoC are complex for most people. I'm sure it's the same for physicists that try to explain black holes to amateur astronomers. I teach photography at the college level and questions concerning DOF and CoC come up at the very least on a weekly basis.
When I need help on an issue of physics or math I discuss my concerns with my fellow colleagues. I approach them with an open mind, ready to learn and grasp the complex concepts we sometimes deal with. It is unfortunate that many of the posters in this thread don't take the time and approach the concepts of DOF with the same concerns and forethought.
The worse thing about the internet is the amount of falsehoods that go unchallenged.
Jeff Donald wrote:
You have posted this repeatedly and many respondents have countered your inaccurate comparisons and illustrations. Nothing can be learned from your experiments. Did you read the link I've posted twice already to Van Walree's site? If not please take the time to do so and respond in an academic fashion that will contribute to the discussion. Your continued posting of the same meaningless thoughts and personal opinions are pointless.
Edited by Jeff Donald on Aug 13, 2005 at 07:26 PM GMT
My explanation is eloquent. It was intended as a thought experiment, but perhaps you should consider actually wasting the paper. You might learn something from it.
EnCapture wrote:
those are 2 different lenses so of course the DOF will be different. the lenses have different viewing angles. if however how simply took a few steps back to achieve the same composition, the DOF remains the same.
That's why using a P&S the DOF is usually large at almost any aperture (i.e the picture is in focus almost to infinity) --because the lens is effectively something like a 7 mm lens.
For the same focal length the DOF is the same --the lens hasn't magically altered it's focal length or powers just because you've got a smaller sensor. The glass is still the same piece of glass.
If you really did get an increase in focal length then you could argue that a really tiny 1 pixel by 1 pixel sensor would give your lens an infinite focal length --clearly absurd.
Volleybob wrote:
Adding CoC, scaling, viewing distance to discussion complicates subject beyond grasp of newbie.
But COC, scaling, and viewing are essential to the discussion of depth-of-field, since they define the parameters by which it is measured and calculated. COC is part of the depth-of-field calculation equation.
Sensor size only changes FoV. Yes, FoV can be traded for shallower DoF, just move the camera closer. Oops! now you've changed the perspective...
This is true, in and of itself. Changing ONLY the sensor size does nothing to the depth-of-field. I don't believe that anybody is disagreeing with that aspect.
But that isn't telling the whole story - if you change sensor size, you will have to either move (which changes perspective, as you've said), or change lens focal lengths (you've changed angle of view, presumably back to what it was with the other format) as well to achieve the same framing of your subject. And when you do either of these two, you've altered a variable in the depth-of-field equation.
Adding CoC, scaling, viewing distance to discussion complicates subject beyond grasp of newbie.
I respectfully disagree. I teach adult education classes in the evening that are for beginners and the concepts of CoC and DOF are not too complicated for beginners. I have beginning photographers that ask all the time why their digital P&S doesn't produce the same images as their film P&S. They don't know or understand DOF or CoC when they walk into the class, but they do when they walk out. In the average class of 10 to 15 students I explain the concepts and reality of DOF and CoC in 30 minutes or less, depending on questions.
Volleybob wrote:
Adding CoC, scaling, viewing distance to discussion complicates subject beyond grasp of newbie.
Whatever concept you are referring to, it is not what the photography world calls DoF. Those parameters are required both to understand the concept and calculate the values of DoF, and it is not an uncomplicated subject. I hope one day you grasp it .
We have tried to explain it to you but clearly this has been a semantic issue - we've been trying to explain DoF and you've been thinking of something else......
This damn thread went 11 page! God, you all aught to be ashamed of yourselves. I think this whole thing is nothing but semantics anyway. But just in case I will be getting a 1Ds Mark II the beginning of next week and I will take some tripod mounted images with the same lens, of the same subject, at the same distance, with the same settings using both bodies and post them here so you all can tell for yourselves. Adios.
Jeff Donald wrote:
I respectfully disagree. I teach adult education classes in the evening that are for beginners and the concepts of CoC and DOF are not too complicated for beginners. I have beginning photographers that ask all the time why their digital P&S doesn't produce the same images as their film P&S. They don't know or understand DOF or CoC when they walk into the class, but they do when they walk out. In the average class of 10 to 15 students I explain the concepts and reality of DOF and CoC in 30 minutes or less, depending on questions.
Jeff, as far as that goes you know damn well that when a 35mm P&S states "120mm lens" it is a 120mm lens, but that a crop sensor (and they all are) digital P&S states "120 mm lens" it's a 120 equivelent lens and the actual focal length is probably closer to 20mm. That is the reason for the long DOF and the poor bokah characteristics. Why are you even thowing that into the mix?
Focal length for the 35mm film P&S Canon Sure Shot 150U Zoom 38-150mm
Lens 38-150mm f/5.6-11.3
Focal length for the digital P&S Canon PowerShot A510
Lens Focal Length 5.8mm - 23.2mm (35mm - 140mm equivalent)
Jeff, as far as that goes you know damn well that when a 35mm P&S states "120mm lens" it is a 120mm lens, but that a crop sensor (and they all are) digital P&S states "120 mm lens" it's a 120 equivelent lens and the actual focal length is probably closer to 20mm.
I'm well aware of that and pointed it out in my second post on page 3. Some P&S cameras use actual mm and some use equivalents, so you have to look carefully to avoid confusion of the students.
That is the reason for the long DOF and the poor bokah characteristics.
The Bokah of a lens is not part of this discussion and I think you're confusing background blur with Bokeh. Both of these concepts are discussed at Van Walree's site. Here is the link to the DOF discussion which helps explain background blur and here is the link to help you understand Bokeh.
I sure hope you explained that to your students.
My day job is a photography professor at a nearby college. I'm always careful to fully explain myself and photographic concepts to my students.
Jeff Donald wrote:
I'm well aware of that and pointed it out in my second post on page 3. Some P&S cameras use actual mm and some use equivalents, so you have to look carefully to avoid confusion of the students.
The Bokah of a lens is not part of this discussion and I think you're confusing background blur with Bokeh. Both of these concepts are discussed at Van Walree's site. Here is the link to the DOF discussion which helps explain background blur and here is the link to help you understand Bokeh.
My day job is a photography professor at a nearby college. I'm always careful to fully explain myself and photographic concepts to my students....Show more →
Then why did you bring that up as a point in this discussion?
Sorry you're confusing my posts with someone else. I've not mentioned Bokeh until just now (my previous post). I did make a reference to background blur that another poster had made and suggested to him (like I suggested to you) that he read the Van Walree's site so he could understand the difference between background blur and DOF.
nsbca wrote:
This damn thread went 11 page! God, you all aught to be ashamed of yourselves. I think this whole thing is nothing but semantics anyway. But just in case I will be getting a 1Ds Mark II the beginning of next week and I will take some tripod mounted images with the same lens, of the same subject, at the same distance, with the same settings using both bodies and post them here so you all can tell for yourselves. Adios.
Unless you change your focal length to accomodate the different sensor size, they will not be the same image. Which would you cut off, the subject's feet or head?
That's the whole gist of the argument - you shoot with a different focal length lens when using a different format in order to obtain the same shot from the same perspective. And when you use a different focal length, you get a very different DOF for the same f/stop.
10DFT wrote:
Unless you change your focal length to accomodate the different sensor size, they will not be the same image. Which would you cut off, the subject's feet or head?
That's the whole gist of the argument - you shoot with a different focal length lens when using a different format in order to obtain the same shot from the same perspective. And when you use a different focal length, you get a very different DOF for the same f/stop.
Wait and watch. Why would I have to cut off the feet or the head?
Jeff Donald wrote:
Sorry you're confusing my posts with someone else.
Don't intentionally try to confuse the issue. You are the poster who was comparing digital P&S cameras to film P&S cameras and bringing the comparison in to make a point about DOF and sensor size without mentioning the focal length variable in the equation.
Don't intentionally try to confuse the issue. You are the poster who was comparing digital P&S cameras to film P&S cameras and bringing the comparison in to make a point about DOF and sensor size without mentioning the focal length variable in the equation.
I think this is the part of one of my previous posts you are referring to:
"I have beginning photographers that ask all the time why their digital P&S doesn't produce the same images as their film P&S."
The above out of context sentence was in response to Volleybob stating the DOF was too complex an issue for beginning photographers. I used the reference to P&S cameras to imply that beginning photographers have an interest in DOF, not that film and digital have no differences. Sorry for your confusion with my posting.
If you had read my second post on page three you'll see that I fully explain why P&S have different DOF and included an explanation of focal length equivalents and how it affects the DOF formula. Since you seem unwilling to review prior posts to refresh your memory I've include part of the post covering P&S cameras that are pertinent to the current discussion.
"Photographers want to make a persons head a certain size. If the head is too small or too large the image is not acceptable by normal standards. The photographer then changes one or two of the variables to make the head size "acceptable" and the DOF increases dramatically. This is best illustrated by looking at the lens on Point and Shoot camera and seeing the 6 mm is the "35mm equivalent" to a 50mm lens. By inserting a 6 into the DOF formula instead of a 50 dramatically increases DOF even after accounting for the magnification change in CoC when printing.'
