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12-06-2020, 11:17 AM   #61
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QuoteOriginally posted by normhead Quote
There ya go... the whole topic adequately explained in way not open to bias or mis-interpretation.

Studying these images is worth more than reading a 10,000 word essay. It always amazes me when people use words to describe readily demonstrable visual phenomena. Why do they do that? It's all about the images.
And it always amazes me those who need to see two or more multi-megabyte images when a single equation of about a dozen bytes suffices.

Moreover, the equation proves the rule for all focal lengths, format sizes, subject distances, and subject sizes. In contrast, the images only verify the rule for a single subject, single distance, and some "equivalent" pair of focal lengths and format sizes.

Perhaps neither of us should be surprised that neither images, words, nor math suffice to convince everyone -- different strokes for different folks!

12-06-2020, 11:28 AM   #62
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QuoteOriginally posted by Ian Stuart Forsyth Quote
Nope I just know that there is no DOF until we first decide how we are going to view it,
Seriously, do you ever even read what you write? DoF exists whether you decide in advance how you are going to view it or not. Your decisions have no bearing on DoF. An image shot at ƒ16 will have more DoF than one shot at ƒ4. No matter what size you view it at.

QuoteQuote:
And it always amazes me those who need to see two or more multi-megabyte images when a single equation of about a dozen bytes suffices.
You can look at and work out the math for all the images you desire. You still have no idea what it will look like until you see the images. You can look at images without math, you can't see the effect of various settings until you take the image.

I often set up my camera, take images at 5 different f-stops, and pick the best image. When you can do that with math, let me know. Until then, maybe consider the math is superfluous to photography, but possibly necessary for those who can't appreciate or are incapable of visual learning.

Everything I learned about DoF I learned without math. When accepted into Ryerson, I didn't even know what DoF was technically, but I knew how to use it to get the pictures I wanted. And that's why I don't ever believe all this theoretical nonsense about DoF. Everything you need, you can see in the images.

There is little more frustrating on the forum than people who suspect something to be true but can't provide images to prove their point. The reason for that being is, quite often people espouse the use of make work formulas, that show theoretical differences that don't hold up in the real world. The may be differences, but they aren't significant enough to be visible? I don't care if there's difference, I only care if I can see a difference, and that is determined only visually. And for many of the things people quibble over, like a 5% increase in resolution, no one has ever shown they make any visual difference at all.

Last edited by normhead; 12-06-2020 at 11:42 AM.
12-06-2020, 01:58 PM   #63
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QuoteOriginally posted by normhead Quote
Seriously, do you ever even read what you write? DoF exists whether you decide in advance how you are going to view it or not. Your decisions have no bearing on DoF. An image shot at 16 will have more DoF than one shot at 4. No matter what size you view it at.
Don't be silly, DOF is a a function of perception, how we are going to view an image will determine how much DOF we will observe and DOF will vary depending on the person doing the viewing.
This is the very reason why they are included into how we model DOF to predict how the setting on our camera will change DOF. This is very basic when it comes to photography funny that this is something you want to argue.

Here is a test done in 2011 showing DOF is a function of how you display an image



The image on the left is shot with a 100mm lens at 4.5 and the image on the right is shot using the very same lens at the very same distance at 2.8

To me they have vary similar DOF as what I can see around 4.5mm of DOF. While the amount of background blur varies the amount of DOF remains the same.

lets look at the DOF calcs




When I take into account how the images are going to be viewed the DOF calcs they pretty much predict what we are seeing when the images are viewed at different enlargements factors ( for these around 1.6 X)

Last edited by Ian Stuart Forsyth; 12-06-2020 at 02:13 PM.
12-06-2020, 02:22 PM   #64
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QuoteOriginally posted by Ian Stuart Forsyth Quote
Don't be silly, DOF is a a function of perception, how we are going to view an image will determine how much DOF we will observe and DOF will vary depending on the person doing the viewing.
Yes and no. Laws of physics drive the equations. Conventions regarding estimates of visual acuity and final magnification drive the actual numbers we use to predict perception. Norm is correct from the position of physics, i.e. when a tree falls in the forest the crash makes recordable noise regardless of whether anybody is there to hear it. My camera records the physical reality in the machine logic sense* regardless of whether anyone ever displays the file.

As for amount and quality of out-of-focus blur for a given distance plus or minus the plane of focus, that is another matter since blur is, by definition, outside the available DOF. The last I heard, that may vary between lenses.


Steve

(...waiting for the inevitable discussion of bokeh balls as being circles of confusion...not from you, ISF...)

* The reason I mentioned machine logic is that the physics of DOF affect performance of cameras that monitor industrial process. It is measurable whether it is perceived or not.


Last edited by stevebrot; 12-06-2020 at 03:00 PM.
12-06-2020, 02:32 PM - 1 Like   #65
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QuoteOriginally posted by Ian Stuart Forsyth Quote
To me they have vary similar DOF as what I can see around 4.5mm of DOF. While the amount of background blur varies the amount of DOF remains the same.
To my eyes, the one on the right has quite a bit less DOF, but perhaps that might change if I move a little further away from the screen.

Below is my avatar photo at the size I originally chose to upload to Flickr (my first share to that site). Perception at reasonable viewing distance is that DOF is fairly narrow, not so with the avatar photo where the entire rose appear in sharp focus. Magnification does its magic.


Pentax K10D, LZOS MC Jupiter-9 85/2.0


Steve
12-06-2020, 03:05 PM   #66
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QuoteOriginally posted by stevebrot Quote
Norm is correct from the position of physics, i.e. when a tree falls in the forest the crash makes recordable noise regardless of whether anybody is there to hear it.
Ya but we are not recording DOF when view at 100% of what a camera can record we are seeing the point that diffraction, lens resolution and camera shake hide the focus plane and everything within that distortion will appear as equally sharp. With less distortion ( a better lens) we see finer detail and this would give us a different appearance of DOF as we can distinguish detail differently.

If we use your analog and add noise from the surrounding forest to hide the sound of the falling tree ( distortion ) and we cannot hear the tree falling does it change the distance the trees from the person hearing it. Of course not and the very same with the focus plane.

There is also a well defined definition of DOF and are you going to argue that we will have to change the -stop based on the film grain used as this would allow us to view the image much closer and see the point at which this distortion creates and equally sharp image?

I have never hear anyone who would use a different -stop on the K5 and the istDS when photographing landscapes

---------- Post added 12-06-2020 at 04:24 PM ----------

QuoteOriginally posted by stevebrot Quote
To my eyes, the one on the right has quite a bit less DOF, but perhaps that might change if I move a little further away from the screen.
I know its hard to see that there is little difference but if we hold what appears to be sharp rather than what is larger verses what is smaller and only focus on edge resolution for how the image is being viewed they are very similar


here you can see the edges with similar resolution
12-06-2020, 03:42 PM   #67
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QuoteOriginally posted by Ian Stuart Forsyth Quote
Ya but we are not recording DOF when view at 100% of what a camera can record we are seeing the point that diffraction, lens resolution and camera shake hide the focus plane and everything within that distortion will appear as equally sharp. With less distortion ( a better lens) we see finer detail and this would give us a different appearance of DOF as we can distinguish detail differently.

I don't know that I said or inferred any of that. As for DOF in the example...I just counted the number of millimeter lines that appeared acceptably sharp at a screen distance of 55cm.*

Thanks for posting the photo again, though I saw it quite well the first time.



Steve

* I should explain that my optometrist told me that my visual acuity is some greater than most people's.
12-06-2020, 07:04 PM   #68
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QuoteQuote:
Here is a test done in 2011 showing DOF is a function of how you display an image
It doesn't change the relationship. If one image has double the DoF, you change the viewing distance or print size, and one still has double the DoF of the other. It's just a different value. So really how is that information in any way useful in determining what f-stop you should shoot at? Or any use at all?

Post a picture where it's good at one viewing distance and size and not so good at different viewing distance and size, just to provide us with some evidence this is any way meaningful.

12-06-2020, 10:17 PM - 2 Likes   #69
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QuoteOriginally posted by stevebrot Quote
Assuming same subject distance and same final magnification
In practical examples Lens breathing can really make a mess of this.
12-06-2020, 11:04 PM   #70
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QuoteOriginally posted by Digitalis Quote
In practical examples Lens breathing can really make a mess of this.
Yes, it might, if effective focal length at focus distance were a consideration.


Steve

(...Throw in an internal focus fixed maximum aperture zoom and everything goes strange...notice no DOF scales on those zooms...)

Last edited by stevebrot; 12-06-2020 at 11:10 PM.
12-13-2020, 12:28 AM   #71
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Thx for the explanation. BTW like your radio equipment. Short wave ?
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