Digital zoom & DOF

[Ysarex]

The depth of field is both the same and different but you wont know until you open the box and look at the metadata.

Er… no.

We’re going round in circles

I’m going to have to admit defeat. As I say, all the depth of field calculators in the world are at odds with what you’re saying, and there is good reason for that—so if you’re bothered about the subject then there is plenty of explanatory material out there.

Of course, it’s completely fine not to care about the technicalities, and just make images that you like the look of, and to use cropping however you like to get the results you want. That’s great. But that doesn’t mean that depth of field works differently for you to how it does for the rest of the universe

I'm focusing on the photo's appearance.

It doesn't work to try and suggest a comparison if the photos have different content and are presented at different magnifications.

 

[Jeff Biscuits]

Again, the uncropped photo appears to have shallower depth of field.

Ok. Whatever you want to see. It appears to me to have greater depth of field. (And there’s a mathematical explanation for that.)

 

[DarnGoodPhotos]

When looking at the photos in isolation, because you wouldn't normally be able to compare them, the uncropped photo appears to have shallower depth of field because it displays noticeably more blurring.

I trust you mean the cropped photo?

Or do you mean something like, “the uncropped photo includes elements that are further out of focus than the cropped image, thus increasing the apparent contrast between the in-focus and out-of-focus areas”?

The uncropped, non-TC photo appears to have shallower depth of field because it displays objects which are more blurred. The effect is similar to an f2 and an f4+ version of the same photo.

That would be fair enough. But that’s not the same as “shallower depth of field”.

Depth of field relates solely to the physical space that has been projected onto the imaging surface. It defines how far away from the focal plane an object needs to be, in that three dimensional space, in order to be perceptibly blurred.

Technically the depth of field hasn't changed because in both photos the aperture is the same, the focal length is the same, the camera to subject distance is the same, and the subject to background distance is the same.

That is technically incorrect. That is not how DOF is defined. You don't understand DOF correctly.

Use this DOF calculator: https://www.cambridgeincolour.com/tutorials/dof-calculator.htm#google_vignette

Put in a set of values and do a DOF calculation (ideally one that doesn't reach infinity).

Now click at the top of the calculator where it says show advanced. Double the first variable Max Print dimension from 10 to 20 and click Calculate.

If the DOF values change then you are technically incorrect.

It's a Schrödinger's DoF situation.

The physical depth of field of your original photo doesn't change just because you cropped later; however, the way the depth of field appears does change.

 

[Ysarex]

When looking at the photos in isolation, because you wouldn't normally be able to compare them, the uncropped photo appears to have shallower depth of field because it displays noticeably more blurring.

I trust you mean the cropped photo?

Or do you mean something like, “the uncropped photo includes elements that are further out of focus than the cropped image, thus increasing the apparent contrast between the in-focus and out-of-focus areas”?

The uncropped, non-TC photo appears to have shallower depth of field because it displays objects which are more blurred. The effect is similar to an f2 and an f4+ version of the same photo.

That would be fair enough. But that’s not the same as “shallower depth of field”.

Depth of field relates solely to the physical space that has been projected onto the imaging surface. It defines how far away from the focal plane an object needs to be, in that three dimensional space, in order to be perceptibly blurred.

Technically the depth of field hasn't changed because in both photos the aperture is the same, the focal length is the same, the camera to subject distance is the same, and the subject to background distance is the same.

That is technically incorrect. That is not how DOF is defined. You don't understand DOF correctly.

Use this DOF calculator: https://www.cambridgeincolour.com/tutorials/dof-calculator.htm#google_vignette

Put in a set of values and do a DOF calculation (ideally one that doesn't reach infinity).

Now click at the top of the calculator where it says show advanced. Double the first variable Max Print dimension from 10 to 20 and click Calculate.

If the DOF values change then you are technically incorrect.

It's a Schrödinger's DoF situation.

The physical depth of field of your original photo doesn't change just because you cropped later;

Yes it does -- the DOF changes. An object that appears within DOF in a photo can appear outside DOF in a cropped version of the photo -- your illustration shows that taking place and you've provided proof that you are wrong.

Here's another example where the DOF is altered by cropping. View the illustration original size.

however, the way the depth of field appears does change.

The way DOF appears is the way DOF is defined.

 

[Ysarex]

If there is less focus then there is more blurring.

But you don’t get to say “look, in this photo an object that’s relatively far from the focal plane is more blurred than an object that’s relatively close to it”. All this means is that the increased blur caused by the enlargement of the image is less than the additional blur incurred by being further away from the focal plane. Take either of those objects and enlarge them and they become more blurred. The fact that one of them now falls outside the region that you choose to view is not relevant.

The reason is irrelevant because you usually cant see the metadata

Metadata has nothing to do with this.

all you can go on is what the photo looks like.

Right.

The photo with more foreground/background blurring will appear to have shallower depth of field like it would with an f2 and f4+ version of the same photo.

Again, you are misunderstanding what depth of field is. The fact that one photo includes objects that are closer to the camera, and are more blurred as a result, categorically does not mean the depth of field is shallower.

Again, the uncropped photo appears to have shallower depth of field.

Again, the uncropped photo appears to have deeper DOF.

 

[Minolta TC-1]

Again, you are misunderstanding what depth of field is. The fact that one photo includes objects that are closer to the camera, and are more blurred as a result, categorically does not mean the depth of field is shallower.

Again, the uncropped photo appears to have shallower depth of field.

Which doesn't matter at all. DOF is the following. You have the focal plane. How much before and after will it still be in focus?

If I take a portrait and put my hand in front of the lens, it will be blurred. If I crop it out, the blurred element is gone. None of that changes the DOF. For example, if I use a 90/f2 or 85/f1.4 on FF, I can get a portrait with eyes in focus and tip of the nose slightly out of focus.

The DOF of the original will be looked at in the context of the person in focus and the hand out of focus is irrelevant. If I cut the photo in half to crop out the hand, enlarge the half 2x to get the same size, then the tip of the nose will be slightly more out of focus because of the enlargement. The eyes are still in focus. The fact that there's a completely blurred hand not shown has nothing to do with it.

 

[jjcha]

People like to talk in theory.

I just take photos.

I took this photo knowing I needed ~1 meter to ~20 meters in reasonably sharp focus.

After 20 meters, I didn't want it in sharp focus, because that's "background" to me.


GFX100RF at F16, focus at 2 meters, DoF of ~1 meter to ~20 meters, assuming a CoC of ~0.038.

I shoot APS-C, full frame, and 44mm x 33mm -- all generally at 28mm full frame equivalent focal length. If I didn't adjust my aperture to deal with depth of field changes, I'd be in trouble very quickly.

There is a reason I am highly attuned to circle of confusion assumptions and various conventions (thank you everyone for clarifying 1/1730 vs 1/1500) - my photography lives or dies by zone focusing.

I see people arguing on the internet - quite frankly there is a lot of ignorance. The principles learned from shooting thousands of shots on the street are simple:

APS-C DoF of 18.3mm at 2 meters at F4.0 is roughly equal to

Full Frame DoF of 28mm at 2 meters at F5.6 is roughly equal to

44mm x 33mm DoF of 35mm at 2 meters at F8.0.

I usually live with my subjects at 1.5 meters to 3 - 5 meters at night (the daylight photo above is an exception). If these statements weren't true, I could not do my photography.




Ricoh GRIII at F4 focus at 2 meters, DoF of ~1.5 meters to 4 meters.

 

[Ysarex]

Again, you are misunderstanding what depth of field is. The fact that one photo includes objects that are closer to the camera, and are more blurred as a result, categorically does not mean the depth of field is shallower.

Again, the uncropped photo appears to have shallower depth of field.

Which doesn't matter at all. DOF is the following. You have the focal plane. How much before and after will it still be in focus?

If I take a portrait and put my hand in front of the lens, it will be blurred. If I crop it out, the blurred element is gone. None of that changes the DOF. For example, if I use a 90/f2 or 85/f1.4 on FF, I can get a portrait with eyes in focus and tip of the nose slightly out of focus.

The DOF of the original will be looked at in the context of the person in focus and the hand out of focus is irrelevant. If I cut the photo in half to crop out the hand, enlarge the half 2x to get the same size, then the tip of the nose will be slightly more out of focus because of the enlargement. The eyes are still in focus. The fact that there's a completely blurred hand not shown has nothing to do with it.

Your hand example is effective.

 

[DarnGoodPhotos]

If there is less focus then there is more blurring.

But you don’t get to say “look, in this photo an object that’s relatively far from the focal plane is more blurred than an object that’s relatively close to it”. All this means is that the increased blur caused by the enlargement of the image is less than the additional blur incurred by being further away from the focal plane. Take either of those objects and enlarge them and they become more blurred. The fact that one of them now falls outside the region that you choose to view is not relevant.

The reason is irrelevant because you usually cant see the metadata

Metadata has nothing to do with this.

all you can go on is what the photo looks like.

Right.

The photo with more foreground/background blurring will appear to have shallower depth of field like it would with an f2 and f4+ version of the same photo.

Again, you are misunderstanding what depth of field is. The fact that one photo includes objects that are closer to the camera, and are more blurred as a result, categorically does not mean the depth of field is shallower.

Again, the uncropped photo appears to have shallower depth of field.

Again, the uncropped photo appears to have deeper DOF.

So if you took the same photo at f2 and f5.6, you think the one with more foreground blurring was f5.6?

 

[The Hat]

It's just a crop.

 

[Ysarex]

If there is less focus then there is more blurring.

But you don’t get to say “look, in this photo an object that’s relatively far from the focal plane is more blurred than an object that’s relatively close to it”. All this means is that the increased blur caused by the enlargement of the image is less than the additional blur incurred by being further away from the focal plane. Take either of those objects and enlarge them and they become more blurred. The fact that one of them now falls outside the region that you choose to view is not relevant.

The reason is irrelevant because you usually cant see the metadata

Metadata has nothing to do with this.

all you can go on is what the photo looks like.

Right.

The photo with more foreground/background blurring will appear to have shallower depth of field like it would with an f2 and f4+ version of the same photo.

Again, you are misunderstanding what depth of field is. The fact that one photo includes objects that are closer to the camera, and are more blurred as a result, categorically does not mean the depth of field is shallower.

Again, the uncropped photo appears to have shallower depth of field.

Again, the uncropped photo appears to have deeper DOF.

So if you took the same photo at f2 and f5.6, you think the one with more foreground blurring was f5.6?

No, I understand how DOF works, and you didn't do that.

Read this post https://www.dpreview.com/forums/post/68315676 by Minolta TC-1. He does a good job of refuting your faulty thinking.