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

[mgates]

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.

I don't think you understand what interpolation is either. Interpolation doesn't change FOV.

Digital zoom is not synomymous with interpolation. You don't get a higher degree of interpolation from a D30 vice a 1D Mk II just because one crops.

You need to think about this more.

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.

Yes and the only way to ensure that holds true in every case is to keep the comparision quality constant. Otherwise resolution is an artificially induced varibale. And as you point out print quality does matter.

No need to vary the focal length or subject distance when you can pull out your trusty scissors and snip the FF negative in the same way the dSLR cropper already snipped it.

DOF never changes with film format because every large format film contains within it all imaginable smaller format images at their same quality level for any given enlargement size.

 

[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?

No, did you read what I wrote at all?

Yes you said you must to enlarge the APS format to a greater degree and that quality doesn't matter.

Then later you said quality does matter because resolution matters. But you disregard that notion when enlarging the cropper more using digital zoom.

You said the exact opposite.

--
Lee Jay
(see profile for equipment)

 

[Barugon]

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.

If I have a scene framed a certain way on a 5D and I crop the image ( I can't "just snip the negative" because there is no negative) then I've just eliminated part of the scene that I had framed. Is that right? Is any part of what I said incorrect?

Assuming that I'm correct so far....

If I wanted to capture the full scene as I had it framed previously, but knowing that I'm going to crop it to APS-C, then I have to somehow shrink the scene so it fits in the area that I intend to crop to, otherwise I loose part of the scene that I wanted to capture. Correct? Or do I need to "just snip the negative" to achieve my goal?

Continuing on as if I'm right....

To shrink the scene in my viewfinder so that it matches APS-C proportions I will either need to physically move my body backwards away from where I have my camera pointed or I'll need to select a shorter focal length. Have I made a mistake yet? Is there some way that a pair of scissors can scale-down the scene for me in my viewfinder?

BTW, not once did I suggest that the size of the sensor has any affect on the lens' properties (but for some inexplicable reason you like to respond to my posts as if I did).

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

http://www.pbase.com/dot_borg

 

[Barugon]

D30, not 30D.

My mistake.

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

http://www.pbase.com/dot_borg

 

[Roger Krueger]

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.

Or if you change distance. Changing lens and/or changing distance
are the only ways to use the entire image and have the same
composition.

Scissors.

Which part of "use the entire image" are you unable to understand?

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

Sure, if you have wildly different lenses, but sticking to similar
fields of view the FF will always have less DOF.

The FF always has an exact APS image within it.

So?

You seem to think you can crop FF to APS and still call it FF. You can't. FF cropped to APS is APS. Otherwise you're ascribing magical properties to unused film. Oddly enough, you'll find that APS and APS have identical 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 can throw half the pixels away without affecting quality? Yeah,
right.

That is right. APS is a smaller format which means it uses less
film area. Cropping FF film to APS size equalizes image quality.

Not if the pixel densities are different. And why should I tolerate equalizing down my FF image to mere APS? Next you'll be having me take sandpaper to my "L" glass so I can compare it to a Holga.

You are left with the exact APS negative.

So what? There is zero difference between a native APS image and a FF image cropped to APS later, assuming equal pixel count.

Sure, there is NO difference between shooting a crop sensor and
cropping from a larger sensor, assuming they have the same pixel
pitch. But if you're happy with that low a pixel count, sell your
FF camera and buy a 300d.

A FF camera might have twice the pixel density as the APS camera.

Real world, FF cameras have a higher pixel count, but lower pixel density than APS cameras. But if you crop an FF camera to APS it'll have less than half of its pixels remaining.

You are confusing variables. Reference film and you will
understand why the format does not affect lens properties.

Right, but almost all lens properties scale with the degree of enlargement. A 35mm lens that resolves 80lp/mm may be sharper than a 4x5 lens that resolves 40 lp/mm, but the 4x5 will be sharper once enlarged to the same size prints . DOF scales similarly, how much blur is tolerable is entirely related to enlargement. DOF on equivalent size prints is the only meaningful comparison. DOF at the sensor is a pointless, confusing concept.

You can't introduce digital zoom into the equation as if it has no
ill affect.

You're the one cropping things, not me. I want to take the entire image from different format cameras, make identical prints (identical size and composition definitely, identical FOV as close as practical), and compare DOF.

 

[mgates]

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.

If I have a scene framed a certain way on a 5D and I crop the image
( I can't "just snip the negative" because there is no negative)
then I've just eliminated part of the scene that I had framed. Is
that right? Is any part of what I said incorrect?

You can snip the negative using any crop tool. Digital adds another variable because some FF cameras are migher density than croppers and some are lower.

But assuming quality is constant like FF film vs APS film then yes a cropper has already snipped away part of FF film's field of viiew.

Assuming that I'm correct so far....

If I wanted to capture the full scene as I had it framed
previously, but knowing that I'm going to crop it to APS-C, then I
have to somehow shrink the scene so it fits in the area that I
intend to crop to, otherwise I loose part of the scene that I
wanted to capture. Correct? Or do I need to "just snip the
negative" to achieve my goal?

Just snip the FF negative. APS film does so by design.

Continuing on as if I'm right....

To shrink the scene in my viewfinder so that it matches APS-C
proportions I will either need to physically move my body backwards

No that is where you have gone astray. An APS film photograph is already a crop from a FF film photograph at a correspondingly lower quality level. To equalize the FOV with quality held constant you don't have to move or change focal length. Just snip the FF negative down to match the lower quality of the APS negative and you are left with the same photograph at the same enlargement degree and the same quality level. DOF is the same.

away from where I have my camera pointed or I'll need to select a
shorter focal length. Have I made a mistake yet? Is there some way
that a pair of scissors can scale-down the scene for me in my
viewfinder?

BTW, not once did I suggest that the size of the sensor has any
affect on the lens' properties (but for some inexplicable reason
you like to respond to my posts as if I did).

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

http://www.pbase.com/dot_borg

 

[Barugon]

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.

If I have a scene framed a certain way on a 5D and I crop the image
( I can't "just snip the negative" because there is no negative)
then I've just eliminated part of the scene that I had framed. Is
that right? Is any part of what I said incorrect?

You can snip the negative using any crop tool. Digital adds
another variable because some FF cameras are migher density than
croppers and some are lower.

But assuming quality is constant like FF film vs APS film then yes
a cropper has already snipped away part of FF film's field of viiew.

Assuming that I'm correct so far....

If I wanted to capture the full scene as I had it framed
previously, but knowing that I'm going to crop it to APS-C, then I
have to somehow shrink the scene so it fits in the area that I
intend to crop to, otherwise I loose part of the scene that I
wanted to capture. Correct? Or do I need to "just snip the
negative" to achieve my goal?

Just snip the FF negative. APS film does so by design.

Continuing on as if I'm right....

To shrink the scene in my viewfinder so that it matches APS-C
proportions I will either need to physically move my body backwards

No that is where you have gone astray. An APS film photograph is
already a crop from a FF film photograph at a correspondingly lower
quality level. To equalize the FOV with quality held constant you
don't have to move or change focal length. Just snip the FF
negative down to match the lower quality of the APS negative and
you are left with the same photograph at the same enlargement
degree and the same quality level. DOF is the same.

away from where I have my camera pointed or I'll need to select a
shorter focal length. Have I made a mistake yet? Is there some way
that a pair of scissors can scale-down the scene for me in my
viewfinder?

BTW, not once did I suggest that the size of the sensor has any
affect on the lens' properties (but for some inexplicable reason
you like to respond to my posts as if I did).

Okay, its clear at this point that you're responding without actually reading my posts. You're interjecting arguments that have nothing to do with what I said. I believe that pretty much everyone else here can understand what I said so I'll just leave it at that.

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

http://www.pbase.com/dot_borg

 

[UnderWater]

Anyways you can see the relationship with a DOF calculator.

You get more DOF with the smaller sensor for the same shot (same shooting position, two different focal length lenses, same framing, same aperture) or you can open up the aperture by the sensor multiplier on the smaller sensor to get the same DOF.

First time I ran across this years ago it was counterintuitive to me so I did the math to convince myself.

Anyways, bottom line is that the DOF differences between the different sensor sizes is over-rated.

--len

 

[mgates]

Anyways you can see the relationship with a DOF calculator.

DOF calculators are wrong in the instance of cropping a smaller negative from a larger one. There is no need to change focal length or subject distance to do that. You have to understand the assumptions before blindly accepting someone else's work.

 

[dave_s93]

But in any case, if you move, there's no way you can get the same
picture (perspective is different) with any lens or any camera
combination. The real equivalence would be to take the pic with
equivalent focal lengths without moving.

The only DOF change directly affected only by sensor size is the
CoC. The one you are pointint out is not just because of sensor
size, but both sensor size and distance to the subject.

Actually, that is not true. The perspective that you get from a 50mm lens on a 1.6x crop camera is the same as the perspective that you get from an 80mm lens on a FF camera, since when you crop, you loose the distortions that are found on the edges. See link:

http://www.dpreview.com/learn/?/Glossary/Optical/Perspective_01.htm

Hope this helps.

 

[Barugon]

Anyways you can see the relationship with a DOF calculator.

DOF calculators are wrong....

No they're not.

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

http://www.pbase.com/dot_borg

 

[SteveHorn]

It is all about the physical size of the lens aperture - and the distances to the objects.

If you stay in the same position and create the same framing by using a longer lens for the larger frame camera, the aperture diameter of the longer lens will be bigger. With a small aperture diameter, the 'view' from all the bits of glass in the front element is almost the same, but with a large aperture, each part of the glass is viewing the scene from a different angle, just because it it bigger. So except for the parts of the image that are in focus, the lens 'sees' the scene from more angles with the big aperture so the image is more fuzzy.

 

[spt_gb]

No need to back up. You can always use the same lens at the same
distance to produce an APS negative of the same quality from a full
frame negative. Whether backing up or changing focal length or
comparing at different quality levels might affect lens properties
is a different question. The question was whether film affects lens
properties.

Erm, no you can't. The same lens, at the same distance on APS and
35mm means that one of the two is incorrectly framed. If it's the
APS camera that is incorrectly framed then you've lost the edges of
the scene forever and nothing can bring them back. If it's the 35mm
camera that is incorrectly framed then all you are saying is that a
35mm frame cropped to 1.6 looks just like a 1.6 crop frame (DUH!).

That is all there is to it. Most professionals would "duh" right
back at you for thinking that digital zoom is the equivalent of
optical zoom.

Most professionals would be slapping you about the head for the idea of framing a 35mm or larger image as if it was APS sized, cropping off the edges off and shouting "behold, it looks the same as APS".

It doesn't matter if you call it digital zoom, optical zoom, enlargement or what have you. If you have enough detail to make a quality print at 8x10 then no arguments about how you got there are important. If you take a 5D image and print it at 8x10 you get about 360DPI (you need to crop it to 5:4). The same shot from a 30D gives you about 298DPI. The human eye can only resolve about 300dpi and this is the normal upper limit for pro grade printers, so in both cases the final output quality is the same, but the APS image has been enlarged more. This extra enlargement reduces the DOF from the 30D shot. If you stick to the same lens and distance the the 5D shot will show extra details from around the borders that the 30D didn't capture and will look to have more DOF.

...

The enlargement size is the same when you crop the film to APS.

THATS the point. You DONT crop 35mm to APS and use the same enlargement factor. You enlarge what you have to your standard size. If you take your method a step further do you realy want to shoot an 8x10 plate, crop it to APS size and say that DOF looks the same? Would you not rather make a contact print from it (enlargement 1:1) in which case you've got hugely more apparent DOF.

 

[spt_gb]

You think that throwing away over half of your captured image ISN'T loosing quality? If you only wanted an APS sized negative then you shoot with APS film, not with 35mm and a pair of scisors.

The more you enlarge the more you show up flaws in lens and film. This is true of any photographic process (digital or film). You keep trying to equalise enlargement rather than print size and this is just plain wrong for DOF comparisons.

DUH again! By definition whenever you crop you lose quality.

Really? Please explain how cropping a piece of full frame film to
APS size makes it "lower quality" than APS film.

 

[saynomore]

You can use any focal length, on any camera, and as long as you and the subject aren't moving the perspective doesn't change. FOV and DOF may change, but perspective doesn't. There is no such thing as a "50mm perspective on 1.6X" or any such concept.

In the case you point out, a 50mm on a 1.6x would give you the FOV of a 80mm on FF, so the picture will have the same FOV and so to keep the same subject size, you wouldn't have to move. You don't need to crop at all, and you still have the same perspective, but only because you didn't move.

On the same cameras, put a 1200mm lens, and don't move, and you still have the same perspective. Very different FOV, but the same perspective. Perspective is independent of FOV or focal length.

But in any case, if you move, there's no way you can get the same
picture (perspective is different) with any lens or any camera
combination. The real equivalence would be to take the pic with
equivalent focal lengths without moving.

The only DOF change directly affected only by sensor size is the
CoC. The one you are pointint out is not just because of sensor
size, but both sensor size and distance to the subject.

Actually, that is not true. The perspective that you get from a
50mm lens on a 1.6x crop camera is the same as the perspective that
you get from an 80mm lens on a FF camera, since when you crop, you
loose the distortions that are found on the edges. See link:

http://www.dpreview.com/learn/?/Glossary/Optical/Perspective_01.htm

Hope this helps.

 

[David J. Littleboy]

You think that throwing away over half of your captured image ISN'T
loosing quality? If you only wanted an APS sized negative then you
shoot with APS film, not with 35mm and a pair of scisors.
The more you enlarge the more you show up flaws in lens and film.
This is true of any photographic process (digital or film). You
keep trying to equalise enlargement rather than print size and this
is just plain wrong for DOF comparisons.

It looks like you've been suckered into discussing a red herring. A very red one.

DOF considerations always presume that the cameras being compared are capable of producing acceptable quality prints of the presumed size for the presumed viewing distance.

So it's wrong to introduce image quality considerations into a DOF discussion. If one of the cameras of concern isn't capable of making an acceptable quality print of the desired size, then DOF doesn't exist, since there's no print to observe the DOF in.

--
David J. Littleboy
Tokyo, Japan

 

[malcolm82]

What about eye resolution?

 

[vor]

Anyways you can see the relationship with a DOF calculator.

DOF calculators are wrong in the instance of cropping a smaller
negative from a larger one. There is no need to change focal
length or subject distance to do that. You have to understand the
assumptions before blindly accepting someone else's work.

Check this out:

http://www.dofmaster.com/dofjs.html

Actual lens focal length: 50mm; selected f-stop: f/2.8; subject distance: 10 ft

DOF for 35mm film: 2.06 ft
DOF for APS film: 1.71 ft

The only change above is in the different film size; focal length, subject distance, and aperture are all the same. This, therefore, is the same as cropping the film. So, please tell us how the DOF calculator is wrong, or what assumptions we're missing.

Best regards,

Victor

 

[Petteri Sulonen]

I thought we put this baby to sleep a while back.

[ http://photo.net/learn/optics/dofdigital/ ]

Petteri
--
[ http://www.prime-junta.net/ ]
[ http://p-on-p.blogspot.com/ ]

 

[vor]

Most professionals would be slapping you about the head for the
idea of framing a 35mm or larger image as if it was APS sized,
cropping off the edges and shouting "behold, it looks the same
as APS".

I would suspect that most professionals are more professional than to be slapping other people over such trivial arguments.

The enlargement size is the same when you crop the film to APS.

THATS the point. You DONT crop 35mm to APS and use the same
enlargement factor. You enlarge what you have to your standard
size. If you take your method a step further do you really want to
shoot an 8x10 plate, crop it to APS size and say that DOF looks the
same? Would you not rather make a contact print from it
(enlargement 1:1) in which case you've got hugely more apparent DOF.

Something that should be kept in mind here, though, is that professionals tend to choose the camera format used for a specific shoot based on the expected final print size. As such, a pro would probably choose 35mm over large format when making prints no bigger than 4x6, but large format over 35mm when making large poster-size prints. The enlargement factor need not be the same in those two cases, but the enlargement factor is not ignored; pros try to keep enlargement factors to a reasonable range.

-v