Velocity Reviews > Same depth of field for digital vs. film

# Same depth of field for digital vs. film

Winston
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Posts: n/a

 11-17-2004
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
Guest
Posts: n/a

 11-17-2004
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" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) om...
> 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

Gisle Hannemyr
Guest
Posts: n/a

 11-17-2004
http://www.velocityreviews.com/forums/(E-Mail Removed) (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?

Michael A. Covington
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Posts: n/a

 11-17-2004

"Winston" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) om...
> 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

Peter Corser
Guest
Posts: n/a

 11-17-2004
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" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) om...
> 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

David J Taylor
Guest
Posts: n/a

 11-17-2004
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

Aerticus
Guest
Posts: n/a

 11-17-2004
Does it matter?

Why assume film DOF has superior qualities?

Aerticus

Roland Karlsson
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Posts: n/a

 11-17-2004
(E-Mail Removed) (Winston) wrote in
news:(E-Mail Removed) om:

> 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

Peter Corser
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Posts: n/a

 11-17-2004
>"Aerticus" <(E-Mail Removed)> wrote in message
>news:spLmd.9\$(E-Mail Removed)...
> 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

Owamanga
Guest
Posts: n/a

 11-17-2004
On 17 Nov 2004 21:41:48 GMT, Roland Karlsson
<(E-Mail Removed)> wrote:

>(E-Mail Removed) (Winston) wrote in
>news:(E-Mail Removed). com:
>
>> 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!