Digital zoom & DOF

[DarnGoodPhotos]

The digital zoom is no different from cropping. The depth of field might look shallower but this just because the same amount fills more of the photo.

If it looks shallower then it is shallower. DOF is defined as what you see under controlled viewing conditions. In your illustration the DOF clearly changes with enlargement. Viewed on my display with the illustration filling the display the same marked location (see arrows) changes from within DOF to outside DOF. The DOF in the exact same image changes with enlargement.

For example, my X100 at 23mm and 50mm, you can see that the lego isn't blurred more on the right.

1 - 23mm (Normal)

2 - 50mm (2X TC)

3 - 50mm (2X TC)

In the left normal photo you cant read the circled stud while on the right TC photo you can because the right foreground has less blurring. On a different kind of photo like portrait with a vertical background they would probably look the same.



--
www.darngoodphotos.com

 

[Jeff Biscuits]

In the left normal photo you cant read the circled stud while on the right TC photo you can because the right foreground has less blurring.

But you’re not comparing the same stud! One of them is at least twice as far away from the focal plane as the other. Compare the same stud and it is more blurred in the right hand image: so while it is physically the same distance from the focal plane, it is more blurred when enlarged. And the same applies to everything that is not precisely on the focal plane. That is a reduction in depth of field, caused by the greater enlargement required by the smaller starting image.

On a different kind of photo like portrait with a vertical background they would probably look the same.

They might not be obviously different (we are after all talking about completely unknown parameters—distance to subject, distance to wall, lens, sensor…) but they will be different. You probably wouldn’t perceive “really heavily blurred” and “a bit more than really heavily blurred” to be much different, but the effect exists nonetheless.

 

[DarnGoodPhotos]

In the left normal photo you cant read the circled stud while on the right TC photo you can because the right foreground has less blurring.

But you’re not comparing the same stud! One of them is at least twice as far away from the focal plane as the other. Compare the same stud and it is more blurred in the right hand image: so while it is physically the same distance from the focal plane, it is more blurred when enlarged. And the same applies to everything that is not precisely on the focal plane. That is a reduction in depth of field, caused by the greater enlargement required by the smaller starting image.

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.

On a different kind of photo like portrait with a vertical background they would probably look the same.

They might not be obviously different (we are after all talking about completely unknown parameters—distance to subject, distance to wall, lens, sensor…) but they will be different. You probably wouldn’t perceive “really heavily blurred” and “a bit more than really heavily blurred” to be much different, but the effect exists nonetheless.

Sure. I just mentioned this because I'm not suggesting that all photos will appear the same when cropped. I dont think you will see much of a difference when you cant see the in and out of focus transition.

--
www.darngoodphotos.com

 

[Ysarex]

The digital zoom is no different from cropping. The depth of field might look shallower but this just because the same amount fills more of the photo.

If it looks shallower then it is shallower. DOF is defined as what you see under controlled viewing conditions. In your illustration the DOF clearly changes with enlargement. Viewed on my display with the illustration filling the display the same marked location (see arrows) changes from within DOF to outside DOF. The DOF in the exact same image changes with enlargement.

For example, my X100 at 23mm and 50mm, you can see that the lego isn't blurred more on the right.

1 - 23mm (Normal)

2 - 50mm (2X TC)

3 - 50mm (2X TC)

In the left normal photo you cant read the circled stud while on the right TC photo you can because the right foreground has less blurring. On a different kind of photo like portrait with a vertical background they would probably look the same.

??????! You're not comparing the same place in the photos -- meaningless. The more enlarged image (right side) shows less within DOF than the less enlarged image (left side).

 

[DarnGoodPhotos]

The digital zoom is no different from cropping. The depth of field might look shallower but this just because the same amount fills more of the photo.

If it looks shallower then it is shallower. DOF is defined as what you see under controlled viewing conditions. In your illustration the DOF clearly changes with enlargement. Viewed on my display with the illustration filling the display the same marked location (see arrows) changes from within DOF to outside DOF. The DOF in the exact same image changes with enlargement.

For example, my X100 at 23mm and 50mm, you can see that the lego isn't blurred more on the right.

1 - 23mm (Normal)

2 - 50mm (2X TC)

3 - 50mm (2X TC)

In the left normal photo you cant read the circled stud while on the right TC photo you can because the right foreground has less blurring. On a different kind of photo like portrait with a vertical background they would probably look the same.

??????! You're not comparing the same place in the photos -- meaningless. The more enlarged image (right side) shows less within DOF than the less enlarged image (left side).

I'm looking at the photos as a whole, The 23mm photo looks like it has shallower depth of field because it displays more foreground blurring.

--
www.darngoodphotos.com

 

[Jeff Biscuits]

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”?

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.

 

[Jeff Biscuits]

I'm looking at the photos as a whole, The 23mm photo looks like it has shallower depth of field because it displays more foreground blurring.

I think I now get what you’re saying, but it’s misunderstanding what depth of field is.

 

[Ysarex]

The digital zoom is no different from cropping. The depth of field might look shallower but this just because the same amount fills more of the photo.

If it looks shallower then it is shallower. DOF is defined as what you see under controlled viewing conditions. In your illustration the DOF clearly changes with enlargement. Viewed on my display with the illustration filling the display the same marked location (see arrows) changes from within DOF to outside DOF. The DOF in the exact same image changes with enlargement.

For example, my X100 at 23mm and 50mm, you can see that the lego isn't blurred more on the right.

1 - 23mm (Normal)

2 - 50mm (2X TC)

3 - 50mm (2X TC)

In the left normal photo you cant read the circled stud while on the right TC photo you can because the right foreground has less blurring. On a different kind of photo like portrait with a vertical background they would probably look the same.

??????! You're not comparing the same place in the photos -- meaningless. The more enlarged image (right side) shows less within DOF than the less enlarged image (left side).

I'm looking at the photos as a whole, The 23mm photo looks like it has shallower depth of field because it displays more foreground blurring.

No. They are images with different content presented at different magnifications. Your thinking is flawed. The photo with the 23mm lens does appear to have deeper DOF.

As for your original comment -- it is well established that cropping an image and changing the degree of enlargement alters DOF and your photos show 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. It's a Schrödinger's DoF situation.

--
www.darngoodphotos.com

 

[Jeff Biscuits]

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.

But the size of the sensor on which you’re capturing the image is not the same. This affects the size of the circle of confusion, which is a factor in the equation that expresses depth of field.

Let me put it this way: have you stopped to consider the fact that every single depth of field calculator disagrees with you?

It's a Schrödinger's DoF situation.

Now I think you’re misunderstanding Schrödinger’s cat as well as depth of field

This is not something that exists in an indeterminate state. It’s provable mathematics.

 

[DarnGoodPhotos]

The digital zoom is no different from cropping. The depth of field might look shallower but this just because the same amount fills more of the photo.

If it looks shallower then it is shallower. DOF is defined as what you see under controlled viewing conditions. In your illustration the DOF clearly changes with enlargement. Viewed on my display with the illustration filling the display the same marked location (see arrows) changes from within DOF to outside DOF. The DOF in the exact same image changes with enlargement.

For example, my X100 at 23mm and 50mm, you can see that the lego isn't blurred more on the right.

1 - 23mm (Normal)

2 - 50mm (2X TC)

3 - 50mm (2X TC)

In the left normal photo you cant read the circled stud while on the right TC photo you can because the right foreground has less blurring. On a different kind of photo like portrait with a vertical background they would probably look the same.

??????! You're not comparing the same place in the photos -- meaningless. The more enlarged image (right side) shows less within DOF than the less enlarged image (left side).

I'm looking at the photos as a whole, The 23mm photo looks like it has shallower depth of field because it displays more foreground blurring.

No. They are images with different content presented at different magnifications. Your thinking is flawed. The photo with the 23mm lens does appear to have deeper DOF.

As for your original comment -- it is well established that cropping an image and changing the degree of enlargement alters DOF and your photos show that.

The primary visual indication of shallower depth of field is more blurring. The uncropped photo displays more foreground blurring. If you only saw the TC photo on the right it would not appear to have very shallow DOF, certainly not f2.

--
www.darngoodphotos.com

 

[Jeff Biscuits]

Is this correct?

Yup

Nuff said ;-)

Y’know… I actually typed an immediate reply to this at the time, saying “oh, it won’t be…” and then chose not to hit the Post button

 

[Jeff Biscuits]

The primary visual indication of shallower depth of field is more blurring.

No, it is not.

Shallower depth of field means that a lesser region to the front and rear of the focal plane appears to be in focus.

I could take a photo with fifty metres of depth of field, and if I had an object an inch in front of the lens it would be extremely blurred. Equally I could take a picture of a wall with only an inch of depth of field and nothing would be blurred.

The uncropped photo displays more foreground blurring.

Because it includes elements that are further from the focal plane, not because the depth of field is shallower.

 

[DarnGoodPhotos]

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.

But the size of the sensor on which you’re capturing the image is not the same. This affects the size of the circle of confusion, which is a factor in the equation that expresses depth of field.

Let me put it this way: have you stopped to consider the fact that every single depth of field calculator disagrees with you?

The primary visual indication of shallower depth of field is greater amount of blurring. The uncropped photo displays more foreground/background blurring, therefore the uncropped photo appears to have shallower depth of field in the same way that an f2 photo appears to have shallower depth of field than an f4+ photo because it displays greater foreground/background blurring.

It's a Schrödinger's DoF situation.

Now I think you’re misunderstanding Schrödinger’s cat as well as depth of field

This is not something that exists in an indeterminate state. It’s provable mathematics.

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

--
www.darngoodphotos.com

 

[DarnGoodPhotos]

The primary visual indication of shallower depth of field is more blurring.

No, it is not.

Shallower depth of field means that a lesser region to the front and rear of the focal plane appears to be in focus.

If there is less focus then there is more blurring.

I could take a photo with fifty metres of depth of field, and if I had an object an inch in front of the lens it would be extremely blurred. Equally I could take a picture of a wall with only an inch of depth of field and nothing would be blurred.

The uncropped photo displays more foreground blurring.

Because it includes elements that are further from the focal plane, not because the depth of field is shallower.

The reason is irrelevant because you usually cant see the metadata; all you can go on is what the photo looks like. 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.

--
www.darngoodphotos.com

 

[Jeff Biscuits]

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

 

[DarnGoodPhotos]

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.

--

www.darngoodphotos.com

 

[Jeff Biscuits]

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.

 

[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.

 

[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.