# Same depth of field for digital vs. film

Discussion in 'Digital Photography' started by Winston, Nov 17, 2004.

1. ### WinstonGuest

Will a digital camera with the same sized sensor as a 35mm film
camera's 24 x 36mm format have the EXACT same depth of field as that
film camera, given everything else is equal, lens, aperture, distance,
etc.

Along the same lines, does a smaller sensor automatically mean it will
have more DOF than one that is slightly larger. In other words will a
lens multiplication factor that is lower (say, 1.1) have less DOF that
one that is higher (say 1.6)?

Thanks,
Winston

Winston, Nov 17, 2004

2. ### Gene PalmiterGuest

Yes ...to both parts. But, I don't know the science of it...just the real
world experience. So lets see what those who know the math have to say about
it. DOF is a function of the aperture. The aperture size is not a fixed
size, but a ratio of the sensor size and something else....distance out to
some point in the lens. So F-stop is the ratio and that stays the same even
when the sensor size and length changes. I think I have most of that
approximately almost near right.

"Winston" <> wrote in message
news:...
> Will a digital camera with the same sized sensor as a 35mm film
> camera's 24 x 36mm format have the EXACT same depth of field as that
> film camera, given everything else is equal, lens, aperture, distance,
> etc.
>
> Along the same lines, does a smaller sensor automatically mean it will
> have more DOF than one that is slightly larger. In other words will a
> lens multiplication factor that is lower (say, 1.1) have less DOF that
> one that is higher (say 1.6)?
>
> Thanks,
> Winston

Gene Palmiter, Nov 17, 2004

3. ### Gisle HannemyrGuest

(Winston) writes:
> Will a digital camera with the same sized sensor as a 35mm film
> camera's 24 x 36mm format have the EXACT same depth of field as that
> film camera, given everything else is equal, lens, aperture,
> distance, etc.

Yes.

> Along the same lines, does a smaller sensor automatically mean it
> will have more DOF than one that is slightly larger. In other words
> will a lens multiplication factor that is lower (say, 1.1) have less
> DOF that one that is higher (say 1.6)?

Yes, provided the /angle of view/ is same in both cases.

But if you keep the focal length constant, a smaller sensor will
give you a more shallow DOF.

The effects of both focal length and sensor size on DOF is shown in
formulas:

http://heim.ifi.uio.no/~gisle/photo/dof.html

--
- gisle hannemyr [ gisle{at}hannemyr.no - http://folk.uio.no/gisle/ ]
========================================================================
When you say you live in the real world, which one are you referring to?

Gisle Hannemyr, Nov 17, 2004
4. ### Michael A. CovingtonGuest

"Winston" <> wrote in message
news:...
> Will a digital camera with the same sized sensor as a 35mm film
> camera's 24 x 36mm format have the EXACT same depth of field as that
> film camera, given everything else is equal, lens, aperture, distance,
> etc.

Yes, of course. There's nothing that could make it different.

Bear in mind however that "depth of field" is not an exact concept. It's a
matter of how much blur you are willing to tolerate. It depends on print
size and what you want your pictures to look like.

> Along the same lines, does a smaller sensor automatically mean it will
> have more DOF than one that is slightly larger. In other words will a
> lens multiplication factor that is lower (say, 1.1) have less DOF that
> one that is higher (say 1.6)?

For the same print size, yes.

--
Clear skies,

Michael A. Covington
Author, Astrophotography for the Amateur

Michael A. Covington, Nov 17, 2004
5. ### Peter CorserGuest

Winston

IIUC the DOF is a factor of the true focal length of the lens (not the
equivalent) and the acceptable "circle of confusion" which is a measure of
the acceptable sharpness (e.g. what is acceptable to you may not be
acceptable to me and vice versa).

Digital compacts have a major problem in DOF being extremely wide due to the
small sensors and very short focal lengths required by these sensors. The
wide angle end is often in the range from 5.5 to 8 mm focal length (probably
equivalent to 34 to 40 mm with multiplication factors of 5 to 7) and whilst
the minute sensor requires a much smaller circle of confusion the DOF is
often incredible (often 1m to inf at f4).

Changing from one film to a different one can have an effect on sharpness in
that technology so I suppose that technically the pitch of the pixels and
the colour of the light may have some effect, but in real world terms on any
given camera the DOF (once you have defined what is acceptable to you) is
defined by the focal length.

Peter
--
Peter & Elizabeth Corser
Leighton Buzzard
Beds UK
"Winston" <> wrote in message
news:...
> Will a digital camera with the same sized sensor as a 35mm film
> camera's 24 x 36mm format have the EXACT same depth of field as that
> film camera, given everything else is equal, lens, aperture, distance,
> etc.
>
> Along the same lines, does a smaller sensor automatically mean it will
> have more DOF than one that is slightly larger. In other words will a
> lens multiplication factor that is lower (say, 1.1) have less DOF that
> one that is higher (say 1.6)?
>
> Thanks,
> Winston

Peter Corser, Nov 17, 2004
6. ### David J TaylorGuest

Peter Corser wrote:
[]
> Digital compacts have a major problem in DOF being extremely wide due
> to the small sensors and very short focal lengths required by these
> sensors.

... either a major problem, or a major plus point for compacts depending on

David

David J Taylor, Nov 17, 2004
7. ### AerticusGuest

Does it matter?

Why assume film DOF has superior qualities?

Aerticus

Aerticus, Nov 17, 2004
8. ### Roland KarlssonGuest

(Winston) wrote in
news::

> Will a digital camera with the same sized sensor as a 35mm film
> camera's 24 x 36mm format have the EXACT same depth of field as that
> film camera, given everything else is equal, lens, aperture, distance,
> etc.

Yes. The classical definitoon of DOF is not depending on sensor
technology
or film/sensor resolution.

But - you can argue that DOF is dependent upon resolution - but that is
not
the classical definition.

> Along the same lines, does a smaller sensor automatically mean it will
> have more DOF than one that is slightly larger.

Interpretation 1:
If you mean that you scale down the entire setup - both sensor and lens
(e.g. a 50mm f2.0 for 35 mm camera and a 25 mm f2.0 for an Olympus E1),
then this is so. The DOF (for a given angle of view) is only a function
of the aperture diameter - and the smaller E1 lens has a smaller aperture
diameter for the same aperture.

Interpretation 2:
If you mean that you keep the same lens and use a smaller sensor, then
it is the oposite. Then the size of the diagonal decreases and the
greater need for high resolution sensor will actually give you less
DOF with a smaller sensor. But - this interpretation is not all that
useful IMHO.

> In other words will a
> lens multiplication factor that is lower (say, 1.1) have less DOF that
> one that is higher (say 1.6)?

Please use the name "crop factor". It is less confusing IMHO.

/Roland

Roland Karlsson, Nov 17, 2004
9. ### Peter CorserGuest

>"Aerticus" <> wrote in message
>news:spLmd.9\$...
> Does it matter?
>
> Why assume film DOF has superior qualities?
>
> Aerticus

Aerticus

Film DOF and digital DOF are identical in theory - it is only the different
characteristics of films and different sensors as well as individual
perception or acceptance which shows differences. Neither is superior to
the other and how could you measure that anyway?.

The problem I was alluding to with digital compacts is the inability to use
differential focus (e.g. throw the background out of focus) - ok, you can do
it in software, but that is just more work (if you are lazy, like me) or may
be felt to be wrong, if you are pedantically of the old school (which I am
not).

When it comes down to it a specific DOF is a part of the characteristics of
any particular lens/camera combination. Fact of life!

Peter
--
Peter & Elizabeth Corser
Leighton Buzzard
Beds UK

Peter Corser, Nov 17, 2004
10. ### OwamangaGuest

On 17 Nov 2004 21:41:48 GMT, Roland Karlsson
<> wrote:

> (Winston) wrote in
>news::
>
>> Will a digital camera with the same sized sensor as a 35mm film
>> camera's 24 x 36mm format have the EXACT same depth of field as that
>> film camera, given everything else is equal, lens, aperture, distance,
>> etc.

>
>Yes. The classical definitoon of DOF is not depending on sensor
>technology
>or film/sensor resolution.
>
>But - you can argue that DOF is dependent upon resolution - but that is
>not
>the classical definition.
>
>> Along the same lines, does a smaller sensor automatically mean it will
>> have more DOF than one that is slightly larger.

>
>Interpretation 1:
>If you mean that you scale down the entire setup - both sensor and lens
>(e.g. a 50mm f2.0 for 35 mm camera and a 25 mm f2.0 for an Olympus E1),
>then this is so. The DOF (for a given angle of view) is only a function
>of the aperture diameter - and the smaller E1 lens has a smaller aperture
>diameter for the same aperture.
>
>Interpretation 2:
>If you mean that you keep the same lens and use a smaller sensor, then
>it is the oposite. Then the size of the diagonal decreases and the
>greater need for high resolution sensor will actually give you less
>DOF with a smaller sensor. But - this interpretation is not all that
>useful IMHO.
>
>> In other words will a
>> lens multiplication factor that is lower (say, 1.1) have less DOF that
>> one that is higher (say 1.6)?

>
>Please use the name "crop factor". It is less confusing IMHO.
>

Considering the different crop factors, I ran some numbers through the
DOF/Area of confusion calculators and the DSLRs with smaller sensor
sizes have a wider apparent DOF than 35mm would at the same f-stop /
lens configuration to achieve the same angle of view (AOV).

I've cut and pasted my findings:

With fictitious lenses to enable an accurate 1.5 ratio: a 72mm lens on
the DSLR vs a 108mm lens on the SLR both with a target focus distance
of 8m at f5.6 should render a similar AOV.

A SLR with a 108mm NL=7.233m FL=8.949m = 1.716m separation
A DSLR with a 72mm NL=6.830m FL=9.653m = 2.823m separation

So, the DOFs are different, in favor of the DSLR as it has a deeper
DOF for the same aperture setting which is helpful when shallow DOF is
a problem. Eg macro photography or for the wide apertures that you
*need* to use on big lenses to get enough light in.

For this combination, according to the tables, it looks like you'd
need to open the lens another two stops on the DSLR to get a similar
shallower DOF of the 108mm SLR.

--
Owamanga!

Owamanga, Nov 17, 2004
11. ### AerticeusGuest

Yup - with you totally.

One of the posts I popped to the makers of PSCS was image difusion running
on a similar basis to a gradient.

Basically to draw a datum line across an image, set a couple of numerical
parameters and apply the blur incrementally based on distance from the datum
line. It has obvious limitations and I think I know what you mean.

Lens blur has a finesse to it

Aerticus

"Peter Corser" <> wrote in message
news:419bc835\$1_3@127.0.0.1...
> >"Aerticus" <> wrote in message
> >news:spLmd.9\$...
>> Does it matter?
>>
>> Why assume film DOF has superior qualities?
>>
>> Aerticus

> Aerticus
>
> Film DOF and digital DOF are identical in theory - it is only the
> different characteristics of films and different sensors as well as
> individual perception or acceptance which shows differences. Neither is
> superior to the other and how could you measure that anyway?.
>
> The problem I was alluding to with digital compacts is the inability to
> use differential focus (e.g. throw the background out of focus) - ok, you
> can do it in software, but that is just more work (if you are lazy, like
> me) or may be felt to be wrong, if you are pedantically of the old school
> (which I am not).
>
> When it comes down to it a specific DOF is a part of the characteristics
> of any particular lens/camera combination. Fact of life!
>
> Peter
> --
> Peter & Elizabeth Corser
> Leighton Buzzard
> Beds UK
>

Aerticeus, Nov 17, 2004
12. ### Guest

In message <j_Jmd.7395\$063.3865@trndny03>,
"Gene Palmiter" <> wrote:

>DOF is a function of the aperture.

Actually, it is more closely tied, mathematically, to magnification.

All other things being equal (pixel spacing, f-stop, etc.), the ratio of
the absolute image size on the sensor to the absolute subject image
determines DOF.

With the same camera and f-stop, a 600mm shot from a distance will have
the same DOF as a 50mm macro up close, if they both have the same
subject size when focused on the sensor.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><

, Nov 18, 2004
13. ### Guest

In message <>,
Gisle Hannemyr <> wrote:

>But if you keep the focal length constant, a smaller sensor will
>give you a more shallow DOF.

Don't you mean "field of view" instead of "focal length"?
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><

, Nov 18, 2004
14. ### Gisle HannemyrGuest

writes:
> Gisle Hannemyr <> wrote:

>> But if you keep the focal length constant, a smaller sensor will
>> give you a more shallow DOF.

> Don't you mean "field of view" instead of "focal length"?

No.

Work out the math with various sensor sizes and constant focal length
(and aperture) - and you'll see that the above statement is correct.
--
- gisle hannemyr [ gisle{at}hannemyr.no - http://folk.uio.no/gisle/ ]
========================================================================
When you say you live in the real world, which one are you referring to?

Gisle Hannemyr, Nov 18, 2004
15. ### Guest

In message <>,
Gisle Hannemyr <> wrote:

> writes:
>> Gisle Hannemyr <> wrote:

>
>>> But if you keep the focal length constant, a smaller sensor will
>>> give you a more shallow DOF.

>
>> Don't you mean "field of view" instead of "focal length"?

>
>No.
>
>Work out the math with various sensor sizes and constant focal length
>(and aperture) - and you'll see that the above statement is correct.

Nope. I don't see anything correct about your statement at all. In
fact, it even looks less correct than it did before, because I just
noticed that you had it backwards for even "FOV".

You can change the size of the recording medium all you want, but if
that is all that changes, DOF does not change in any way, whatsoever.
It only changes the size of the focused image.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><

, Nov 18, 2004
16. ### George E. CawthonGuest

Peter Corser wrote:
> Winston
>
> IIUC the DOF is a factor of the true focal length of the lens (not the
> equivalent) and the acceptable "circle of confusion" which is a measure of
> the acceptable sharpness (e.g. what is acceptable to you may not be
> acceptable to me and vice versa).
>
> Digital compacts have a major problem in DOF being extremely wide due to the
> small sensors and very short focal lengths required by these sensors. The
> wide angle end is often in the range from 5.5 to 8 mm focal length (probably
> equivalent to 34 to 40 mm with multiplication factors of 5 to 7) and whilst
> the minute sensor requires a much smaller circle of confusion the DOF is
> often incredible (often 1m to inf at f4).
>
> Changing from one film to a different one can have an effect on sharpness in
> that technology so I suppose that technically the pitch of the pixels and
> the colour of the light may have some effect, but in real world terms on any
> given camera the DOF (once you have defined what is acceptable to you) is
> defined by the focal length.
>
> Peter

Thank God, I thought I had died and gone to a different universe and
all of my knowledge and intuition was no longer relevant in this new
universe. I could not see how the sensor size has anything to to
with depth of field. Maybe someone got depth of field confused with
field of view.

As you pointed out, focal length is the primary determination of depth
of field, all the rest just has to do with overall sharpness which is
quite different from depth of field.

Most of the confusion in lenses with digital cameras seems to be the
result of the silly "35 mm equivalent" nonsense. A lens of a specific
focal length provides an image of exactly the same size regardless of
the focal plane medium. Because the medium is very small in most
digital cameras, the viewing and printing magnification is much
greater with digital cameras. This puts one into a perspective that
they are not use to, i.e., you are view 16x or greater enlargements at
very close distances.

George E. Cawthon, Nov 18, 2004
17. ### Roger N. Clark (change username to rnclark)Guest

Owamanga wrote:
> On 17 Nov 2004 21:41:48 GMT, Roland Karlsson
> <> wrote:
>
>
>> (Winston) wrote in
>>news::
>>
>>
>>>Will a digital camera with the same sized sensor as a 35mm film
>>>camera's 24 x 36mm format have the EXACT same depth of field as that
>>>film camera, given everything else is equal, lens, aperture, distance,
>>>etc.

>>
>>Yes. The classical definitoon of DOF is not depending on sensor
>>technology
>>or film/sensor resolution.
>>
>>But - you can argue that DOF is dependent upon resolution - but that is
>>not
>>the classical definition.
>>
>>
>>>Along the same lines, does a smaller sensor automatically mean it will
>>>have more DOF than one that is slightly larger.

>>
>>Interpretation 1:
>>If you mean that you scale down the entire setup - both sensor and lens
>>(e.g. a 50mm f2.0 for 35 mm camera and a 25 mm f2.0 for an Olympus E1),
>>then this is so. The DOF (for a given angle of view) is only a function
>>of the aperture diameter - and the smaller E1 lens has a smaller aperture
>>diameter for the same aperture.
>>
>>Interpretation 2:
>>If you mean that you keep the same lens and use a smaller sensor, then
>>it is the oposite. Then the size of the diagonal decreases and the
>>greater need for high resolution sensor will actually give you less
>>DOF with a smaller sensor. But - this interpretation is not all that
>>useful IMHO.
>>
>>
>>>In other words will a
>>>lens multiplication factor that is lower (say, 1.1) have less DOF that
>>>one that is higher (say 1.6)?

>>
>>Please use the name "crop factor". It is less confusing IMHO.
>>

>
>
> Considering the different crop factors, I ran some numbers through the
> DOF/Area of confusion calculators and the DSLRs with smaller sensor
> sizes have a wider apparent DOF than 35mm would at the same f-stop /
> lens configuration to achieve the same angle of view (AOV).
>
> I've cut and pasted my findings:
>
> With fictitious lenses to enable an accurate 1.5 ratio: a 72mm lens on
> the DSLR vs a 108mm lens on the SLR both with a target focus distance
> of 8m at f5.6 should render a similar AOV.
>
> A SLR with a 108mm NL=7.233m FL=8.949m = 1.716m separation
> A DSLR with a 72mm NL=6.830m FL=9.653m = 2.823m separation
>
> So, the DOFs are different, in favor of the DSLR as it has a deeper
> DOF for the same aperture setting which is helpful when shallow DOF is
> a problem. Eg macro photography or for the wide apertures that you
> *need* to use on big lenses to get enough light in.
>
> For this combination, according to the tables, it looks like you'd
> need to open the lens another two stops on the DSLR to get a similar
> shallower DOF of the 108mm SLR.

But for equal comparison, the DSLR would be magnified 1.5x
more to view it at the same size (e.g. a print). The the circle
of confusion must be 1.5x smaller in order to have similar DOF
after that magnification. The factor 2.823/1.716 = 1.645,
close to the 1.5 ratio. With this in mind, I believe the
two systems would essentially be equal. (But I haven't
gone through the match in detail.)

Roger

Roger N. Clark (change username to rnclark), Nov 18, 2004
18. ### Dave MartindaleGuest

writes:

>You can change the size of the recording medium all you want, but if
>that is all that changes, DOF does not change in any way, whatsoever.
>It only changes the size of the focused image.

DOF does change - if what you are measuring is the DOF on a
constant-sized print. When you reduce the sensor size, you need to
enlarge the image more to get a constant-sized print. And for a
constant circle of confusion size in the print, you need a smaller CoC
on the sensor. That, in turn, reduces the depth of field.

Dave

Dave Martindale, Nov 18, 2004
19. ### Dave MartindaleGuest

"Roger N. Clark (change username to rnclark)" <> writes:

>But for equal comparison, the DSLR would be magnified 1.5x
>more to view it at the same size (e.g. a print). The the circle
>of confusion must be 1.5x smaller in order to have similar DOF
>after that magnification. The factor 2.823/1.716 = 1.645,
>close to the 1.5 ratio. With this in mind, I believe the
>two systems would essentially be equal. (But I haven't
>gone through the match in detail.)

I think you'll find that the different circle of confusion was included

The way the math works is this: If you use a sensor that is 1/2 the
size, and keep the FOV the same, you need to reduce lens FL by a factor
of 2 as well. When you divide FL by 2, you increase DOF by a factor of
4 *at the same CoC size*, because DOF is inversely proportional to FL
squared. But the sensor is half the size, so the CoC must also be half
the size, so the actual DOF increase is 4/2 = 2. The two systems are
*not* equal in DOF when you hold FOV, f/number, and print size constant.

Dave

Dave Martindale, Nov 18, 2004
20. ### Gisle HannemyrGuest

writes:
> In message <>,
> Gisle Hannemyr <> wrote:
>> writes:
>>> Gisle Hannemyr <> wrote:

>>>> But if you keep the focal length constant, a smaller sensor will
>>>> give you a more shallow DOF.

>>> Don't you mean "field of view" instead of "focal length"?

>> No.
>>
>> Work out the math with various sensor sizes and constant focal length
>> (and aperture) - and you'll see that the above statement is correct.

> Nope. I don't see anything correct about your statement at all. In
> fact, it even looks less correct than it did before, because I just
> noticed that you had it backwards for even "FOV".

What are your grounds for saying that?

As I've said - I've computed the DOF from standard optical formulas
found in textbooks that teach optics. I've also checked this
experimentally by comparing DOF of shots taken with a Kodak DCS-460
(1.3X crop) with shots taken with a Canon G5 (4.8x crop).

> You can change the size of the recording medium all you want, but if
> that is all that changes, DOF does not change in any way,
> whatsoever. It only changes the size of the focused image.

The DOF is dependent upon the relative size the so-called circle of
confusion (CoS) to recording media. With the the same focal length,
etc. the CoS stays the same size. If you crop to meke your media
smaller, its relative size becomes larger - which results in a
more shallow DOF.
--
- gisle hannemyr [ gisle{at}hannemyr.no - http://folk.uio.no/gisle/ ]
========================================================================
When you say you live in the real world, which one are you referring to?

Gisle Hannemyr, Nov 18, 2004