How does sensor size produce a shallower DOF?...

[Lee Jay]

The D2X even has selectable levels of digital zoom on top of the
built-in crop factor. Do you contend that its lens has two DOFs
simultaneously?

Yes. In fact, as I've said, cropping, be it digitally or with film, affects DOF, when you keep the same final print size.

--
Lee Jay
(see profile for equipment)

 

[Barugon]

you take the same picture (exactly the same framing!) with a FF and
a crop camera at the same aperture? I think there will be less DOF
with the FF, right?

Only if you change lenses. Changing lenses on one but not the
other can produce any result you want on DOF.

There is no need to change lenses. Full frame film can be cropped
to APS size without affecting the quality of the final enlargement
or the lens.

You're arguing just for the sake of argument. If he wanted to frame a scene that he intended to crop to APS-C proportions then he would have to back up or us a shorter lens to fit the scene, as it was framed in the full 24x36 sensor, in the APS-C area. There is no magic he can perform to get around this.

--
Whoever said 'a picture is worth a thousand words' was a cheapskate.

http://www.pbase.com/dot_borg

 

[mgates]

The D2X even has selectable levels of digital zoom on top of the
built-in crop factor. Do you contend that its lens has two DOFs
simultaneously?

Yes. In fact, as I've said, cropping, be it digitally or with
film, affects DOF, when you keep the same final print size.

Ok so you do accept that there are two ways to compare.

1 - You can use digital zoom to equalize print size in which case there is a change in DOF not corresponding to format but to the quality decrease you induced.

2 - You can stay optically neutral by snipping the FF film negative (or final print) to APS size and keep your print size constant. In the quality-neutral comparison film format never has an effect on optics.

A word of caution. If you accept digital zoom as a non-varuable than you can zoom either format. That opens the door to get any DOF result you wish from either print.

 

[jason48]

It's all about distance to the subject.

 

[Lee Jay]

Ok so you do accept that there are two ways to compare.

Sure - the right way and the wrong way.

1 - You can use digital zoom to equalize print size in which case
there is a change in DOF...

It's not digital zoom, it's enlargement.

...not corresponding to format but to the
quality decrease you induced.

No, the change would be the same even if the original had 1 billion pixels.

2 - You can stay optically neutral by snipping the FF film negative
(or final print) to APS size and keep your print size constant. In
the quality-neutral comparison film format never has an effect on
optics.

It's also two different sized outputs. That's not a 1-for-1 comparison.

--
Lee Jay
(see profile for equipment)

 

[Lee Jay]

It's all about distance to the subject.

No it's not. That's only one of the important variables.

If you want to get right down to it, DOF is dependent on subject distance, FOV, entrance pupil diameter, final viewing size and viewing distance.

--
Lee Jay
(see profile for equipment)

 

[mgates]

Also, I don't believe any DSLRs have digital zoom.

Every dSLR with less than a FF sensor.

Except they have more photo-sites per millimeter, so that's not
true either.

A 1Ds MkII has substantially smaller pixels than a D30. So now what?

The answer is that your focal length and focus distance DO affect
depth of field.

Only if you first believe that digital zoom is optical zoom. The
optically correct way to compare is to stick to optical zoom. That
is crop to APS instead of vice versa.

I don't know too many people who bought a full frame DSLR just so
they could crop all their images to APS-C proportions. That sort of
defeats the benefit of full-frame, don't you think?

I think most photographers do realize there are enlargement limits when using smaller format films. The same holds true for digital zoom.

 

[mgates]

Ok so you do accept that there are two ways to compare.

Sure - the right way and the wrong way.

1 - You can use digital zoom to equalize print size in which case
there is a change in DOF...

It's not digital zoom, it's enlargement.

So the D2X uses "enlargement" not digital zoom?

...not corresponding to format but to the
quality decrease you induced.

No, the change would be the same even if the original had 1 billion
pixels.

2 - You can stay optically neutral by snipping the FF film negative
(or final print) to APS size and keep your print size constant. In
the quality-neutral comparison film format never has an effect on
optics.

It's also two different sized outputs. That's not a 1-for-1
comparison.

By cropping FF film to APS size the film negatives are exactly the same size and quality level.

The fact that you have to use digital zoom on one picture and not the other proves your equations are bad. That is why you have to concede that any one lens attached to a D2X has two simultaneous DOFs. It doesn't. The simple solution is the correct solution. Film format has no effect on lens DOF.

 

[mgates]

you take the same picture (exactly the same framing!) with a FF and
a crop camera at the same aperture? I think there will be less DOF
with the FF, right?

Only if you change lenses. Changing lenses on one but not the
other can produce any result you want on DOF.

There is no need to change lenses. Full frame film can be cropped
to APS size without affecting the quality of the final enlargement
or the lens.

You're arguing just for the sake of argument. If he wanted to frame
a scene that he intended to crop to APS-C proportions then he would
have to back up or us a shorter lens to fit the scene,

Huh? Just snip the negative.

as it was
framed in the full 24x36 sensor, in the APS-C area. There is no
magic he can perform to get around this.

--
Whoever said 'a picture is worth a thousand words' was a cheapskate.

http://www.pbase.com/dot_borg

 

[Lee Jay]

So the D2X uses "enlargement" not digital zoom?

No, printing does.

By cropping FF film to APS size the film negatives are exactly the
same size and quality level.

So what? Print an ISO 400 35mmfilm shot 8x10 and an ISO 25 APS film shot 8x10 and the APS film shot will still have less DOF.

Film format has no effect on lens DOF.

At constant f-stop, focal length and subject distance it does, as you have been shown mathematically, conceptually, and photographically.

--
Lee Jay
(see profile for equipment)

 

[mgates]

That is incorrect. Film size does not affect optics.

No, but film size does affect depth-of-field.

This is the crux of the disagreement. Since you can always snip the negative to equalize both FOV and quality you are simply wronga about that.

That's what the equations say and that's what the optical evidence
says. It's the truth. If you don't want to believe that, then
that's your choice. But the rest of us will still continue to tell
the truth to those who ask like the OP.

The equaltions assume that digital zoom is the same as optical zoom
which is wrong. If you equate digital and optical zoom as the same
than you can get any DOF relationship you wish.

No the equations assume no such thing. You are confused again.

Enlarge the full frame picture to 10 feet by 15 feet then crop a 4
x 6 inch photograph from the middle. Now you would have to say
that the full frame has lower DOF versus APS. Unless you first
accept that digital zoom isn't free.

Did you read about how there have to be enough pixels to resolve
the CoC or didn't you?

So if we put a 1Ds II up agaist a D30 than you would say that full frame DOF is lower?? Eventually you have to hold something constant.

To get the end result you want you are now changing lenses, sensor or film density, and the degree of digital zoom in the final print. Wouldn't it be easier to admit that lens DOF is not affected by scissors?

 

[Lee Jay]

That is incorrect. Film size does not affect optics.

No, but film size does affect depth-of-field.

This is the crux of the disagreement. Since you can always snip
the negative to equalize both FOV and quality you are simply wronga
about that.

Right...cropping affects DOF - just like changing format does.

So if we put a 1Ds II up agaist a D30 than you would say that full
frame DOF is lower??

No, larger, with the same f-stop, subject distance and focal length.

Eventually you have to hold something
constant.

Sure - focal length, f-stop, subject distance, and final print size.

To get the end result you want you are now changing lenses, sensor
or film density, and the degree of digital zoom in the final print.
Wouldn't it be easier to admit that lens DOF is not affected by
scissors?

You just said it is above (and you were right)!

--
Lee Jay
(see profile for equipment)

 

[mgates]

So the D2X uses "enlargement" not digital zoom?

No, printing does.

Ok so you admit that you were using digital zoom but discounting it as having no effect. In that case enlarge the Ff image to a bill board size then snip a 4 x 6 from the middle. No change in quality and now it has less DOF than the APS sensor printed at 4 x 6.

So what? Print an ISO 400 35mmfilm shot 8x10 and an ISO 25 APS
film shot 8x10 and the APS film shot will still have less DOF.

Ok so add ISO as a variable you need to get the results you want.

Film format has no effect on lens DOF.

At constant f-stop, focal length and subject distance it does, as
you have been shown mathematically, conceptually, and
photographically.

Not if you are cropping from one format to get the other.

The same argument is inherent to the question of whether APS dSLRs crop or optically magnify. You say magnify. I say crop.

The truth is they can do either if you are willing to vary print quality. In the quality-constant case of film they crop. Same is true here. If you are willing to vary print quality than you can aritficially induce a change in DOF. That isn't due to format but rather to the use of digital zoom or moving the enlarger farther away from the paper. Changing print quality to get the result you want is not a valid way to compare dSLRs or film cameras.

 

[mgates]

That is incorrect. Film size does not affect optics.

No, but film size does affect depth-of-field.

This is the crux of the disagreement. Since you can always snip
the negative to equalize both FOV and quality you are simply wronga
about that.

Right...cropping affects DOF - just like changing format does.

Great then we agree that scissors change DOF. So FF film always has the same DOF as APS film once snipped down to the same quality level and enlargement size.

 

[Lee Jay]

Ok so you admit that you were using digital zoom but discounting it
as having no effect. In that case enlarge the Ff image to a bill
board size then snip a 4 x 6 from the middle. No change in quality
and now it has less DOF than the APS sensor printed at 4 x 6.

If you want to call interpolation for printing "digital zoom" then fine. You're the only one. Regardless, as long as you can resolve the CoC, the quality of the image is irrelevant to DOF which renders the rest of your musings irrelevant.

--
Lee Jay
(see profile for equipment)

 

[Lee Jay]

Great then we agree that scissors change DOF. So FF film always
has the same DOF as APS film once snipped down to the same quality
level and enlargement size.

No, enlargement is what matters, not quality. Cropping causes a change in enlargement for the same final print size and that changes CoC.

This holds true even with infinite resolution in both cases.

--
Lee Jay
(see profile for equipment)

 

[mgates]

Great then we agree that scissors change DOF. So FF film always
has the same DOF as APS film once snipped down to the same quality
level and enlargement size.

No, enlargement is what matters, not quality.

Ok will you then admit that your change in DOF is induced exclusively by your quality reduction? And without that quality reduction you cannot get the results you desire?

Cropping causes a
change in enlargement

No the printer does.

Scissors do not enlarge but they do keep print quality constant.

for the same final print size and that
changes CoC.

This holds true even with infinite resolution in both cases.

 

[Lee Jay]

Great then we agree that scissors change DOF. So FF film always
has the same DOF as APS film once snipped down to the same quality
level and enlargement size.

No, enlargement is what matters, not quality.

Ok will you then admit that your change in DOF is induced
exclusively by your quality reduction? And without that quality
reduction you cannot get the results you desire?

No, did you read what I wrote at all? You said the exact opposite.

--
Lee Jay
(see profile for equipment)

 

[Barugon]

A 1Ds MkII has substantially smaller pixels than a D30. So now what?

I think you better double check that.

--
Whoever said 'a picture is worth a thousand words' was a cheapskate.

http://www.pbase.com/dot_borg

 

[Lee Jay]

A 1Ds MkII has substantially smaller pixels than a D30. So now what?

I think you better double check that.

D30, not 30D.

--
Lee Jay
(see profile for equipment)