November 25, 2014, 04:23:49 PM

Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.


Messages - ecka

Pages: 1 ... 17 18 [19] 20 21 ... 46
271
"Whether or not regions outside the focal plane appear sharp...that's DoF" - That applies to your eyes, not the original image.

Yes, it still applies to the original image. Tell me...how do you calculate your (incorrect) concept of the "DoF" of 'the original image'.  I'd like to see the math behind that, if you could share it.  Also, what do you even call THAT THING - because it's not the DoF, by definition.

Regardless, while a tree falling in the forest with no one around to hear it does, in fact, make a sound, a photograph without someone to look at it is a completely meaningless collection of 0's and 1's or an equally meaningless collection of developed silver halide grains in an emulsion. The moment someone views it, all of my points about CoC apply...and that, for all purposes relevant to photographs, is the real end of the discussion.

Imagine that you are a cyborg and you see the world through cameras instead of eyes. One camera has 8mp APSC sensor from 20D and another one has 21mp FF sensor from 5D2 (yes, it's weird, you must be made in China, or something). Both with 40mm f/2.8 lenses. You see everything in clearest details up to a single pixel, all of them, all the time. FF camera has 60% wider FoV, but with both lenses focused at the same distance you would see that they both produce the same DoF.
This is a very simplified concept (no need to tell me that), because I don't want to waste any more time on this, but it is real and correct. That's how your camera sees it and renders the DoF. The question is not "How do my eyes deal with DoF?". It is "How the camera does it?". It may not be useful for thumbnails and snapshots, but there is a need for it in photography with extremely shallow DoF and a lot of cropping, like macro (where you can't bring it back if it's oof).

272
I suggest you to read all my posts in this thread, it might help to understand my position (if you didn't already).
Z-axis resolution? Where did that come from? The only thing that sensor gathers is the light to determine a color for each pixel. Everything else is just information manipulation. If you really don't understand how to define "the sharpest area", then you should study the principles of CDAF, it's all there.

I did read them, and it appears that you don't really understand what DoF is, or at least such understanding isn't coming across in your posts.  For example, "...CoC is about perception. DoF is not, it is about information..., and several iterations thereof.  That seems to sum up your argument, but that statement is fundamentally wrong. You cannot determine DoF without a CoC value, either arbitrarily chosen or empirically determined. DoF is based on CoC and other factors, so if you believe that you can determine DoF without CoC, you don't understand what DoF means.

As for 'the sharpest area', that's the focal plane, the plane in space at which the lens is focused. It's a plane, with effectively no depth (although practically, it has some - just as real lenses aren't the infinitely thin lenses we pretend they are for optical calculations).  Everything in front and behind that plane is less sharp, progressively more so at increasing distance along the optical axis. Whether or not regions outside the focal plane appear sharp...that's DoF, and it is affected by several factors, including CoC.

I understand the physics and if I don't quote books and articles, or post links for others to go read something, it doesn't mean that I don't understand a thing. I'm using my own head, because it is science, not a religion. Science provides tools, but you cannot use the same one for everything.
Does the CoC theory work for upscaling images? - No.
Are imaging sensors rendering DoF in a way you described - "a plane, with effectively no depth" where "everything in front and behind that plane is less sharp"? - No.
"Whether or not regions outside the focal plane appear sharp...that's DoF" - That applies to your eyes, not the original image. Think about it. It's like photographing a photograph.
End of the discussion ;).

273
I'm not asking about the illusion of sharpness, I'm asking about the information that camera can capture in the sharpest area.

Of course that's related to pixel size (but less spatial information than the pixel size suggests, due to AA filter effects, lens aberrations, etc.).

The question is, how do you define the 'sharpest area'?

Not all sensors have AA filters, not all are based on Bayer filter technology.
The sharpest area carries the highest amount of information about reality, compared to the rest of the image.

True, but your definition is something of a tautology.  In terms of the real world being captured by the image sensor as sampled by the lens, how do you define 'sharpest area'?  Specifically, does that area have 'depth' relative to the sensor?  Pixel size represents the least quantifiable unit of XY resolution. What about Z-axis resolution?  After all, the latter is what this thread is about...

I suggest you to read all my posts in this thread, it might help to understand my position (if you didn't already).
Z-axis resolution? Where did that come from? The only thing that sensor gathers is the light to determine a color for each pixel. Everything else is just information manipulation. If you really don't understand how to define "the sharpest area", then you should study the principles of CDAF, it's all there.

274
I'm not asking about the illusion of sharpness, I'm asking about the information that camera can capture in the sharpest area.

Of course that's related to pixel size (but less spatial information than the pixel size suggests, due to AA filter effects, lens aberrations, etc.).

The question is, how do you define the 'sharpest area'?

Not all sensors have AA filters, not all are based on Bayer filter technology.
The sharpest area carries the highest amount of information about reality, compared to the rest of the image.

275
Metaphorically speaking, it appears that many people are trapped within the circle of confusion, when it comes to discussions of DoF.

1. The formulas used to calculate DoF all contain CoC as a variable.
2. CoC is dependent on the observer's visual acuity, viewing distance, and output size.

Therefore,

3. DoF is dependent on the observer's visual acuity, viewing distance, and output size.

It's really that simple.

As for Ecka's argument about one pixel, the typically assumed values for CoC, and the practical range of CoC values for other print sizes and viewing distances, are much larger than a single pixel, so spatial quantization is not an issue.

I'm not asking about the illusion of sharpness, I'm asking about the information that camera can capture in the sharpest area.

276
So here we go. Once that optical physics hits the sensor it's no longer optical, it's information. The sensor cannot capture the infinitely thin plane of focus made of sharp points. Instead, it captures everything between the two distances where "a circle" has the size of a pixel or smaller, so everything in that range is same sharp, because there can't be anything sharper than a pixel. At that level, enlarging the image isn't going to decrease the DoF, only soften it, because there is no hidden information.
How do we call THAT THING? The sharpest area between the two distances where "a circle" meets the pixel?

Hey Ecka, I was in a similar state of skepticism here for a while so I just want to help get you where I am now using some common sense.

Forget all the technical stuff about aperture and sensor size for a second and let's just think about this from a simpler perspective. Imagine we just took a picture of a friend. You look at the picture later at 100% on your 30" computer monitor and realize that you accidentally focused on their nose, so their eyes are slightly out of focus. Wouldn't you agree that the plane of focus is on the nose, but doesn't extend to the eyes? Yes of course.

Now let's imagine the friend we took the photo of wants to post that photo to Facebook, and so you post it and it becomes their new profile photo. The whole time you're thinking man that photo wasn't even in focus, but then you go onto their Facebook page, and voila, nobody can even tell if their eyes are in focus because the photo's so small. Basically, the photo looks great. Now I think we can agree that as far as we can tell, their profile picture is in focus. Which would mean that either:

A. You uploaded the wrong picture
B. Magic
C. Our DOF changed because we're now looking at a much smaller picture

And just in case you're not sure. It's obviously B.   ;D

Thank you for trying, but I think the answer is F.

F. You are trying to answer a question I didn't ask.
F. "It doesn't matter" - is not an answer.
F. You don't need a DSLR for shooting thumbnails.
F. Now I know who uses the 720x480 small JPEG shooting format :).
F. Perhaps, my English is so bad, that nobody can understand what I'm saying :). Here's a picture:

What is A-B?

277
DOF is subjective?  Hmm.  If my DOF is 8 feet in a photo, that is, 8 real-life feet out in the field, how in the world does that ever change after I take the photo??  8 feet is 8 feet isn't it? 

Actually, I wouldn't even need to take the photo.  The DOF is still 8 feet.  :)

Are you suggesting that by being subjective, it could be 8 feet, or 6 feet, or 10 feet, or 7.23838383 feet?  How silly.

It seems you think that based on your equipment, there's a 'slice' of the photo that's in perfect focus, say 3.8 feet in front of where you focused, and 4.2 feet behind it, then WHAM like magic at 4.3 feet behind the focal plane, everything gets blurry.  That's not how it works.

Light from the plane of focus (which is best approximated by a plane in the geometric sense - 2D and infinitely thin) is focused on the image sensor (we're ignoring field curvature, of course).  Everything outside that plane, even a few millimeters, is blurry...and the further from the focal plane, the blurrier it gets. That's optical physics.  Whether it looks blurry to you depends on viewing size and distance and your visual acuity.

Tell me - how do you know your hypothetical shot has that 'real' 8 foot DoF?  Did you use a DoF calculator?  That calculator determines the 8 foot DoF based on an assumed specific print size and viewing distance (commonly 8x10" viewed at 1 foot).  Change those assumptions, you change the calculated DoF.

So here we go. Once that optical physics hits the sensor it's no longer optical, it's information. The sensor cannot capture the infinitely thin plane of focus made of sharp points. Instead, it captures everything between the two distances where "a circle" has the size of a pixel or smaller, so everything in that range is same sharp, because there can't be anything sharper than a pixel. At that level, enlarging the image isn't going to decrease the DoF, only soften it, because there is no hidden information.
How do we call THAT THING? The sharpest area between the two distances where "a circle" meets the pixel?

278
... I thought that DoF is the thickness of the sharp focus plane your camera can capture (how is it called then?)...
... the thickness in reality, not in the picture.

...There is no such thing as an 'objective' DoF...

Do we need a new definition here? Because I'm pretty sure that OP was asking about THAT THING, not the CoC.

The plane of focus has no depth. Imagine it as a sheet of the thinnest paper, only much thinner. Everything in front of, and behind, that sheet of paper is less sharp than whatever is on the sheet of paper. Because of limitations to our eyesight something very close to the paper might look in focus, but it isn't, at some point as you move towards the paper things become more obviously out of focus, you have now surpassed your DoF/CoC criteria, but, step back and you again can't see the differences because your eyesight can't resolve it.

I agree that the focus plane of an optical image projection is thinner than it looks like. That's what the CoC thing is all about. However, the sensor resolution is limited and it has it's smallest possible dot size which is a pixel and which is a constant for a given camera.

Maintain a reproduction size and viewing distance ratio such that the CoC (point at which you can't see the difference between a point and a circle) and you can go as big, or as small, as you'd like.

No, you cannot do that. It could only apply to a camera with an infinite number of pixels. If a pixel is too big, then it becomes a square. If it's too small, then it disappears.
In all my statements I assumed that both FF and APSC sensors had the same pixel pitch. Otherwise, even the same format cameras (same sensor size) with different megapixel numbers (like 12 vs 36) should have different DoF/CoC characteristics.

279
... I thought that DoF is the thickness of the sharp focus plane your camera can capture (how is it called then?)...
... the thickness in reality, not in the picture.

...There is no such thing as an 'objective' DoF...

Do we need a new definition here? Because I'm pretty sure that OP was asking about THAT THING, not the CoC.

280
Also here, http://www.josephjamesphotography.com/equivalence/ for a very detailed insight into sensor sizes and their interaction with focal length, dof, aperture and iso. Yes, even iso has a crop factor!
Privatebydesign, thanks for the great link. Lots of fun explanations in there. However, I'm still not sure how print size and viewing distance affect DOF. Is there another explanation somewhere, or maybe some examples?

Btw, I've tried just resizing some of my photos on my monitor and seeing if they seem to have more/less DOF and can't really tell a difference...maybe I'm doing it wrong.

Here is an example. I took this image for an artists show, it was printed to 46"x31". As a 700px web image most would agree the zip picture left, by her right cheek, is within acceptable focus, at f7.1 with a 100mm lens it is well within a dof calculators range. The second image is what that zip looks like when I printed it at 46" and viewed from the same distance. Clearly it is not now in acceptable focus. The only thing that has changed is the subject magnification. We have increased the CoC to such an extent that it no longer holds true, we can clearly differentiate between a point and a circle. To bring it back into acceptable focus we all we need to do is increase our viewing distance, step back from your monitor, across a room, and the zip will become sharp again.

Cool isn't it?  :)

This is only an illusion of sharpness. The truth is what really matters (the information). Looking at the print from far away only proves that human vision is very limited. At close-up you can see all the information captured by your camera, both sharp and blurry parts. So, sharpness = information. Then from the distance you see much much less information despite that it looks sharper. This kind of sharpness ≠ information. This trick is about the CoC of your eyes, DoF has nothing to do with it.

281
EOS Bodies - For Stills / Re: EOS-M sharper than 6D?
« on: July 18, 2013, 01:14:05 PM »
Another possible reason - cheap UV filters.

He used the same lens for both cameras.  I sort of think he would have mentioned putting on a cheap UV filter for the 6D shots and taking it off for the EOS M shots, don't you?  ;)

Yes, I thought the same thing. However, nobody here did mention this possibility, so I did :).

282
EOS Bodies - For Stills / Re: EOS-M sharper than 6D?
« on: July 18, 2013, 12:55:15 PM »
Did you use something weird to clean your 6D sensor?

That's a good thought - maybe something dried and left a film (sorry) over the sensor?

That, or even damaging it.
Another possible reason - cheap UV filters.

283
EOS Bodies - For Stills / Re: EOS-M sharper than 6D?
« on: July 18, 2013, 12:40:56 PM »
Did you use something weird to clean your 6D sensor?

284
Shrinking the picture simply makes it's details imperceptible to you.

If I may, can I suggest that this one sentence sums up some of the disagreement in this thread.   DoF is, in fact, a concept that is rooted in human visual perception.  DoF is defined as the distance in front of and behind the plane of focus that appears in focus to a human being.  The calculation requires assumptions regarding human visual acuity, print size, and viewing distance.

I believe, others can correct me if I'm wrong, it is also implicitly assumed that the print size and resolution is such that the individual pixels in the print are too small for the viewer to see them at the assumed print size and viewing distance.  If the pixels are visible then the entire image would not appear sharp.  That is why sensor resolution does not appear in the calculation.

So yes,  print size matters and yes, if you print small enough the entire image would "magically" appear sharp.  "Appear" is the operative word in that statement but it is relevant because "appears sharp" is fundamental to the concept of DoF.  If you also shrunk yourself down, your visual acuity would likely also change so in fact DoF would be the same.

And it is a concept.  It is a defined value based on some reasonable assumptions.  DoF is not something that exists independent of human vision and is not a strictly defined measurement like mass, distance, size, etc.

If you're looking for a physically defined parameter, it exists.  That is focus distance.  The distance from the image plane that is precisely in focus (in practical terms it would be maximally in focus because there is no perfect focus).  And there is only one distance that is maximally in focus... every plane in front of and behind the focus plane is less focused.  If human visual acuity was infinite and the resolution of a print was infinite you would be able to see the tiniest difference in sharpness.  But that's not the case, more than just the exact plane of focus appears sharp and we can define the depth in the image that appears sharp... i.e. Depth of Field.

I don't know. I disagree, that when I photograph a ruler which clearly shows that the DoF is, let's say, ~15mm, I must let the shrink size decide that the DoF is actually half a meter or that I was shooting at hyperfocal and I'm crazy :).
I thought that DoF is the thickness of the sharp focus plane your camera can capture (how is it called then?). Turns out I was wrong, it is what anyone wants it to be and if it can't be, then just get a better printer :D.
I say, if you have to shrink your images to make everything look sharp, then you are using the wrong camera format.
DoF area is sharp, but sharpness ≠ DoF

285
No. In reality there is nothing that is a 0. Zero is not a thing, zero is just a tool in mathematics.

You are wrong about DOF but I will let others argue about it. But as a mathematician, I strongly object the statement that zero is not a thing, and that there is noting at zero. How many 200-400 lenses do you own?

Quote
Every point has dimensions and it can be represented as an image of at least 1 pixel,

What if you are shooting film?

I don't use superteles.
Film has it's minimum dot size that can be captured.

Pages: 1 ... 17 18 [19] 20 21 ... 46