Digital Depth of Field

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Mike

Just read an article (Digital Photography Made Easy, UK publication,
pg 31) that basically says the depth of field is different for images
taken with a digital camera than for a film camera. It said that if I
had a f2.8 lens with a digital camera that the final image would have
more of a depth of field near f14.

Is that correct?

If so, is there a link to the technical reason that the sensors behave
differently than film in this regard?

Would the same be true for a digital SLR with a f2.8 marco lens,
basically meaning you cannot do shallow depth of field with digital?
 
Mike said:
Just read an article (Digital Photography Made Easy, UK publication,
pg 31) that basically says the depth of field is different for images
taken with a digital camera than for a film camera. It said that if I
had a f2.8 lens with a digital camera that the final image would have
more of a depth of field near f14.
Is that correct?
If so, is there a link to the technical reason that the sensors behave
differently than film in this regard?
Would the same be true for a digital SLR with a f2.8 marco lens,
basically meaning you cannot do shallow depth of field with digital?
Click to expand...

Probably about correct for a digital compact, which have (very) short focal
length lenses.
Definitely not correct for a DSLR which behaves similarly to a film camera -
give or take a crop factor of 1.3x to 1.7x, or none at all.
 
Depth of field is really caused by the design of the human eye and brain.
What we perceive as depth of field is dependent on the focal length of the
lens, the aperature of the lens, and the circle of confusion (this latter is
dependent on the aperature size in the camera).

So, as the focal length of the compact digital cameras is so short, the
depth of the field that one sees must be greater. However, since we use
35mm lenses in the digital SLRs, the depth of field is only affected by the
circle of confusion. The circle of confusion might be smaller for the
digital format (and hence the depth of field might be greater), but I
haven't seen any discussion of the topic.

Jim
 
Mike said:
Just read an article (Digital Photography Made Easy, UK publication,
pg 31) that basically says the depth of field is different for images
taken with a digital camera than for a film camera. It said that if I
had a f2.8 lens with a digital camera that the final image would have
more of a depth of field near f14.

Is that correct?
Click to expand...

Sort of. The DOF of a digital camera will be the same as a film camera
with the same focal length lens used at the same aperture WHEN the size of
the sensor and film area is the same.

Most (all?) consumer digital cameras use sensors smaller than the
standard 35 mm film so they tend to have more DOF than a 35 mm camera, just
as a 35 mm camera has more DOF than a medium format camera and much more
than a 8x10 camera all using the same focal length lens to cover the entire
imaging area.
If so, is there a link to the technical reason that the sensors behave
differently than film in this regard?
Click to expand...

See above.
Would the same be true for a digital SLR with a f2.8 marco lens,
basically meaning you cannot do shallow depth of field with digital?
Click to expand...

Sure you can, but, like a 35 vs. a large format camera, you will need a
larger aperture lens.
 
Just read an article (Digital Photography Made Easy, UK publication,
pg 31) that basically says the depth of field is different for images
taken with a digital camera than for a film camera. It said that if I
had a f2.8 lens with a digital camera that the final image would have
more of a depth of field near f14.

Is that correct?
Click to expand...

I can't see how it would be any different from film to digital. The
laws of optics remain the same.
 
Most (all?) consumer digital cameras use sensors
smaller than the
standard 35 mm film so they tend to have more DOF than a 35 mm camera, just
as a 35 mm camera has more DOF than a medium format camera and much more
than a 8x10 camera all using the same focal length lens to cover the entire
imaging area.
Click to expand...

Not true. The field of view changes, not the DOF. A 45mm lens on a 6x7
camera has a wide angle view (about 22 mm 35mm equivalent) but has the same
DOF as a 45mm lens on a 35mm which has a standard FOV.
 
That depends on the focal length of the lens. If you have the same focal
length the dof will be the same at every aperture setting., but most digital
cameras have very small sensors and very short focal length lenses.
Consequently they have more dof.

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Several almost complete answers posted....

DOF is related to f/no and magnification**. The reason digicams tend
to have higher DOF is they have a higher magnification**,

The DSLR that is anything except "full frame" still has the
effect--albeit less prononounced.

** technically, it is DEmagnification---ie the ratio of image size to
object size. The point is that the larger the number, the greater the
DOF

Just read an article (Digital Photography Made Easy, UK publication,
pg 31) that basically says the depth of field is different for images
taken with a digital camera than for a film camera. It said that if I
had a f2.8 lens with a digital camera that the final image would have
more of a depth of field near f14.

Is that correct?

If so, is there a link to the technical reason that the sensors behave
differently than film in this regard?

Would the same be true for a digital SLR with a f2.8 marco lens,
basically meaning you cannot do shallow depth of field with digital?
Click to expand...

**************************
Mark Herring, Pasadena, Calif.
Private e-mail: Just say no to "No".
 
Jackson said:
Most (all?) consumer digital cameras use sensors
smaller than the

Not true. The field of view changes, not the DOF. A 45mm lens on a 6x7
camera has a wide angle view (about 22 mm 35mm equivalent) but has
the same DOF as a 45mm lens on a 35mm which has a standard FOV.
Click to expand...


You cut off this part of my original message:

" Sort of. The DOF of a digital camera will be the same as a film camera
with the same focal length lens used at the same aperture WHEN the size of
the sensor and film area is the same."

Maybe I did not make it all that clear. The assumption when comparing
DOF of different film sizes is that a lens of a focal length is chosen which
covers the equivalent angle of view. After all what use is a comparison of
an ultra wide angle lens on one camera to a telephoto on another when what
you want to do is take a picture of aunt Gert and uncle Fred?

Clearly we don't compare a digital with a 35-40 mm lens to a 35 mm
camera with a 35 mm or lens to a 4x5 with a 35 mm lens. We compare the
digital with a 35-40 to a 35mm with about 50 to a 4x5 with about 135mm
lenses.

Here are a few sites with information and on line computers of DOF

http://www.wrotniak.net/photo/dof/

http://www.trenholm.org/hmmerk/DOFR.html

http://medfmt.8k.com/brondof.html

http://www.mapril.net/dof/dof.htm
 
I think this is a total oversimplification. Depth of field does depend
on the actual focal length of the lens. Now, in general the smaller the
format size, the smaller the focal length. Thus, an oversimplification
is that since a digital camera USUALLY has a smaller image format than
35mm (aren't ALL film cameras 35mm? :-) ) than DOF of digital is
different than for a 35mm film camera. However, there ARE small format
film cameras. A digital camera would have the same DOF as a film camera
of similar focal length and similar resolution (circle of confusion).

So, NO, digital does not have different DOF than film. Small format
cameras do have different DOF than large format films.
 
Jackson said:
Most (all?) consumer digital cameras use sensors
smaller than the



Not true. The field of view changes, not the DOF. A 45mm lens on a 6x7
camera has a wide angle view (about 22 mm 35mm equivalent) but has the same
DOF as a 45mm lens on a 35mm which has a standard FOV.
Click to expand...

Most things people say about depth of field are right in some
circumstances and wrong in others, and this is no exception. Depth of
field is specified by well know formulas and depends on a variety of
factors. One of the most important is the maximal acceptable circle of
confusion. But this is based on how much you expect to enlarge the
image. Generally, a 6 x 7 image will be enlarged less than half as much
as a 35 mm image. As a result, one can tolerate a larger coc. That
means that in some circumstances, at least, you get more depth of field
with a 45 mm lens in 6 x 7 than a 45 mm lens in 35 mm. However, since
there are other factors invovled, one would have to specify just what
was being compared to come to the correct conclusion.

The formulas governing depth of field, while not specially complex as
mathematics, are too complicated to describe in words. Atempts to do so
often lead to misconceptions.
 
OK... Here's MY question on the depth of field question:

If I use my Olympus C5050z at 35mm fl equivalent on 35mm cameras, will I
have the same depth of field on both cameras?

If I use my OLY at the equivalent of 105 mm on a 35mm camera, will I get the
same depth of field on each camera?

I think that is the only practical way of asking this question. What will
the resultant images be like?

Thom Tapp
 
Randall Ainsworth said:
I can't see how it would be any different from film to digital. The
laws of optics remain the same.
Click to expand...

The laws of optics are the same, but to figure a DOF, you need a
Circle of Confusion dimention. With film, pluck it from what ever
floats your boat, with-in reason. A digital aray almost totally
defines this due to its construction.

--
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+61 (08) 9257-1001 Kalamunda.
West Australia 6076
comp.os.vms,- The Older, Grumpier Slashdot
Raw, Cooked or Well-done, it's all half baked.
EPIC, The Architecture of the future, always has been, always will be.
 
Thom said:
OK... Here's MY question on the depth of field question:

If I use my Olympus C5050z at 35mm fl equivalent on 35mm cameras,
will I have the same depth of field on both cameras?
Click to expand...

No. The olympus will have more DOF
If I use my OLY at the equivalent of 105 mm on a 35mm camera, will I
get the same depth of field on each camera?
Click to expand...

Same as above.
I think that is the only practical way of asking this question. What
will the resultant images be like?
Click to expand...

Much the same. The DOF while different will not be greatly different.
You may not even notice.
 
Thom said:
OK... Here's MY question on the depth of field question:

If I use my Olympus C5050z at 35mm fl equivalent on 35mm cameras, will I
have the same depth of field on both cameras?
Click to expand...

If you are focused at the same subject distance, no. You will have the
same depth of field as your 35 mm lens stopped down approximately an
additional 4 stops.
If I use my OLY at the equivalent of 105 mm on a 35mm camera, will I get the
same depth of field on each camera?
Click to expand...

Same answer.
I think that is the only practical way of asking this question. What will
the resultant images be like?
Click to expand...

For some subjects, such as portraits, there may not be a large
difference, but for others, such as those in which you focus at some
distance, the difference will be dramatic and should be rather obvious
to you.
 
Leonard said:
If you are focused at the same subject distance, no. You will have
the same depth of field as your 35 mm lens stopped down
approximately an additional 4 stops.
Click to expand...

Four stops! How small is that sensor on the 5050Z?
 
Joseph Meehan said:
Four stops! How small is that sensor on the 5050Z?
Click to expand...

It is approximately 1/5 the dimensions of a 35 mm frame. Thus when the
lens is set to a "35 equivalent" focal length of 50 mm, the true FL is
about 10 mm. At a given subject distance and f/number, you'll have
about 5 times as much DOF from the digicam. To get the same DOF from
the 35 camera, you need to multiply the f-number by about 5.

For example, f/2 on the digicam gives the same DOF as f/10 (round to
f/11) on the 35 mm camera.

Dave
 
Dave said:
It is approximately 1/5 the dimensions of a 35 mm frame.
Click to expand...

The Olympus web site list the size as (in inch) 1/1.8” (.55”) CCD which
is about .99 sq inches a 35 mm images size is about 1.75" x .75" or about
1.31". That computes to about 3/4 not 1/5.
 
Joseph Meehan said:
The Olympus web site list the size as (in inch) 1/1.8” (.55”) CCD which
is about .99 sq inches a 35 mm images size is about 1.75" x .75" or about
1.31". That computes to about 3/4 not 1/5.
Click to expand...

Oops. Consumer camera CCD sizes are arbitrary random numbers that are names,
not dimensions, of the particular sizes.

http://www.dpreview.com/learn/?/Glossary/Camera_System/Sensor_Sizes_01.htm

FWIW, the 35mm frame diagonal is 43mm, so 1/1.8" is 43/8.93 = 4.8 times
smaller, and 2/3" is 3.9 times smaller.

David J. Littleboy
Tokyo, Japan
 
Joseph said:
The Olympus web site list the size as (in inch) 1/1.8” (.55”) CCD which
is about .99 sq inches a 35 mm images size is about 1.75" x .75" or about
1.31". That computes to about 3/4 not 1/5.
Click to expand...

The listed size of the CCD is misleading. I don't know what that are
specifying, but it doesn't tell you the actual dimensions of the sensor
array.

You can find an approximation to the actual size by looking at their
equivalent 35 mm focal lengths. For my Olympus 3040, they tell me that
an actual focal length of 7.1 is equivalent to a 35 mm focal length of
35 mm and an actual focal length of 21.3 is equivalent to 105 mm. I
think the 5050 is similar. 35/7.1 = 105/21.3 ~ 4.93. Since the
aspect ratios are different for the Oly and a 35 mm full frame, it is
not clear which lengths they are comparing, but the answers would still
come out in the range 4-5.
 
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