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

[saynomore]

...how this has gone so long! But after all this, and you ultimately stating that these people here don't know about the difference between digital and optical zoom, I don't know if there's any hope for you. Especially when you refer to these guys debating it with you.

What they're trying to tell you is that it doesn't matter. DOF is based on acceptable sharpness, not absolute image quality. When you run into a picture that already doesn't offer acceptable sharpness (by cropping and enlarging to the same size -- your "digital zoom"), then your problem is not of DOF anymore. But as long as you can do it and still conserve acceptable sharpness in a print the same size as the FF print, then DOF works as described by so many people already.

A 1.6 cropped camera has to magnify or enlarge 1.6 times more than
a FF camera to get the same sized image like an 8x10. That is how
it works.

As I said. Many think digital zoom is optical zoom. It is not.

All things equal, an APS camera snips quality to produce apparent
focal length increase. That is why, all things equal, the price is
lower. That isn't optical zoom (full frame magnification) it is
digital zoom (cropping away quality).

I have to say. I am surpised that so many in the 1/5 forum don't
know the difference between digital and optical zoom.

 

[mgates]

Could you define for us how you define quality in regards to DOF?
It seems to be something about resolution / pixels / pixel density

The same way as you. But in my world digital zoom (snip snip) is never a substitue for a change to full frame focal length.

Why? Because allowing the snipping of one camera negative but not the other can never be sensibly argued.

 

[mgates]

...how this has gone so long! But after all this, and you
ultimately stating that these people here don't know about the
difference between digital and optical zoom, I don't know if
there's any hope for you.

Optical zoom isn't bad. It is cheaper and cheaper is good. But please don't confuse it with, or substitute it for, a change in full frame focal length.

Especially when you refer to these guys
debating it with you.

What they're trying to tell you is that it doesn't matter. DOF is
based on acceptable sharpness, not absolute image quality. When you
run into a picture that already doesn't offer acceptable sharpness
(by cropping and enlarging to the same size -- your "digital
zoom"), then your problem is not of DOF anymore. But as long as you
can do it and still conserve acceptable sharpness in a print the
same size as the FF print, then DOF works as described by so many
people already.

A 1.6 cropped camera has to magnify or enlarge 1.6 times more than
a FF camera to get the same sized image like an 8x10. That is how
it works.

As I said. Many think digital zoom is optical zoom. It is not.

All things equal, an APS camera snips quality to produce apparent
focal length increase. That is why, all things equal, the price is
lower. That isn't optical zoom (full frame magnification) it is
digital zoom (cropping away quality).

I have to say. I am surpised that so many in the 1/5 forum don't
know the difference between digital and optical zoom.

 

[saynomore]

It's just that for DOF definitions it doesn't come into the equation! IT DOESN'T MATTER.

Acceptable sharpness, YES.

Original image resolution, NO (until you lose acceptable sharpness).

...how this has gone so long! But after all this, and you
ultimately stating that these people here don't know about the
difference between digital and optical zoom, I don't know if
there's any hope for you.

Optical zoom isn't bad. It is cheaper and cheaper is good. But
please don't confuse it with, or substitute it for, a change in
full frame focal length.

Especially when you refer to these guys
debating it with you.

What they're trying to tell you is that it doesn't matter. DOF is
based on acceptable sharpness, not absolute image quality. When you
run into a picture that already doesn't offer acceptable sharpness
(by cropping and enlarging to the same size -- your "digital
zoom"), then your problem is not of DOF anymore. But as long as you
can do it and still conserve acceptable sharpness in a print the
same size as the FF print, then DOF works as described by so many
people already.

A 1.6 cropped camera has to magnify or enlarge 1.6 times more than
a FF camera to get the same sized image like an 8x10. That is how
it works.

As I said. Many think digital zoom is optical zoom. It is not.

All things equal, an APS camera snips quality to produce apparent
focal length increase. That is why, all things equal, the price is
lower. That isn't optical zoom (full frame magnification) it is
digital zoom (cropping away quality).

I have to say. I am surpised that so many in the 1/5 forum don't
know the difference between digital and optical zoom.

 

[Robert 55]

are you or are you not saying the number of pixels [aka pixel density] is relevant for DOF calculations?

Could you define for us how you define quality in regards to DOF?
It seems to be something about resolution / pixels / pixel density

The same way as you. But in my world digital zoom (snip snip) is
never a substitue for a change to full frame focal length.

Why? Because allowing the snipping of one camera negative but not
the other can never be sensibly argued.

 

[malcolm82]

Its not the larger sensor that causes the shallower depth of field, just the fact that those larger aperture lenses are only available for the larger sensor.

I know you understand this, but i think the way you wrote it doesnt get this point across.

I blame the canon marketting nonsense for this... Have you read about their new safety zoom feature?

 

[mgates]

It's just that for DOF definitions it doesn't come into the
equation! IT DOESN'T MATTER.

Acceptable sharpness, YES.

Original image resolution, NO (until you lose acceptable sharpness).

The point is you never get a change in sharpness nor resolution from sniping with scissors.

 

[mottjr]

After following this discussion for the last 2 days, I have come to the conclusion that the Circle of Confusion is remarkably similar to the Wheel of Samsara. This discusion just goes round and round with people repeating the same thing over and over and nobody listening to anyone else.

-Jim

 

[Rock Lee]

nt = no text

--
Pbase:
http://www.pbase.com/robotzer0

Comments are welcomed.

 

[Rock Lee]

nt = no text

--
Pbase:
http://www.pbase.com/robotzer0

Comments are welcomed.

 

[mgates]

are you or are you not saying the number of pixels [aka pixel
density] is relevant for DOF calculations?

Pixel density be higher in either the full frame dSLR or the cropping dSLR. It is an uncontrolled variable in the digital discussion. Though not in the film discussion.

Both film cameras and dSLRs crop capture area (negative size if you will) to save money. But for the cost differential, FF would always be the answer since every FF photo contains within it the APS photo.

Money-saving digital zoom (cropping) is not a valid way to vary full frame focal length. It should never be confused as such in DOF equations. Othersise, "Would you like to change this equation's answer using scissors?" would be the final option for every hardware combination.

 

[malcolm82]

There are some practical limitations why this is not usually
possible, however. For small sensors, you'd end up with very fast
f-numbers. Lenses with very fast f-numbers are very hard to
produce with good optical qualities because you can't scale one of
the needed parameters - the refrative index of the available
materials. If we had materials of arbitrary refractive index then
ultra-fast, ultra-short lenses would be practical. But, for now,
they aren't so scaling the sensor size up to avoid such lenses is
more cost effective.

I think you overestimate the problem here, a 1.6x crop lens with f/1.8 would not have to be shorter than a full frame lens with f/2.8 so the refractive index wouldnt need to be higher. If you look at the large difference between focal length and true length of the lens with wide angle lenses you can see that it is not a problem to refract the light coming in from the wider angles just a little more to fit on the smaller sensor, this already has to be done with wide angle lenses on 1.6x crop even at the same f-number since they are much further than 1/1.6th the distance from the sensor because of the standard 35mm lens mount so the larger aperture wouldnt change the distance that much. I think these larger aperture lenses might just be a little worse than the ff equivalents and perhaps just slightly larger.