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Depth of field

 
 
Armando
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      11-18-2005
Apologies if this is a rehash, I searched on all the related terms I could
think of first...

In a "real" camera (sorry about that), the f-stop setting of the lens
affects the DOF because of the physical size of the aperture. How is
"f-stop" handled on a digital camera? My guess has always been that it's
just a electrical tweak to the overall brightness of the image, and not an
actual "sphincter" in the lens. A friend has suggested that they could
actually use an LCD shutter, with concentric rings set to transparent or
opaque, to get an actual physical-size thing going, with real DOF.

I confess I've not tried any actual tests to see for myself, but maybe
there's a discussion here while I'm getting around to it...

Armando


 
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223rem
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      11-18-2005
Armando wrote:
> Apologies if this is a rehash, I searched on all the related terms I could
> think of first...
>
> In a "real" camera (sorry about that), the f-stop setting of the lens
> affects the DOF because of the physical size of the aperture. How is
> "f-stop" handled on a digital camera? My guess has always been that it's
> just a electrical tweak to the overall brightness of the image, and not an
> actual "sphincter" in the lens.


Digital SLRs use same lenses as film SLRs!

Non SLR digital cameras also should use mechanical
iris (DOF modulation would not be possible by simply
simply modulating the amplification of the sensor signal).

I believe that What digital cameras dont have is mechanical
shutters--it is done electronically.
 
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Scott W
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      11-18-2005

223rem wrote:
> Armando wrote:
> > Apologies if this is a rehash, I searched on all the related terms I could
> > think of first...
> >
> > In a "real" camera (sorry about that), the f-stop setting of the lens
> > affects the DOF because of the physical size of the aperture. How is
> > "f-stop" handled on a digital camera? My guess has always been that it's
> > just a electrical tweak to the overall brightness of the image, and not an
> > actual "sphincter" in the lens.

>
> Digital SLRs use same lenses as film SLRs!
>
> Non SLR digital cameras also should use mechanical
> iris (DOF modulation would not be possible by simply
> simply modulating the amplification of the sensor signal).
>
> I believe that What digital cameras dont have is mechanical
> shutters--it is done electronically.


In fact digital cameras also have shutters and need them, otherwise you
get blooming.
There is an electronic aspect to it but you do need a shutter, which is
what wears out first in most DSLRs.

Scott

 
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Joseph Meehan
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      11-18-2005
Armando wrote:
> Apologies if this is a rehash, I searched on all the related terms I
> could think of first...
>
> In a "real" camera (sorry about that), the f-stop setting of the lens
> affects the DOF because of the physical size of the aperture. How is
> "f-stop" handled on a digital camera? My guess has always been that
> it's just a electrical tweak to the overall brightness of the image,
> and not an actual "sphincter" in the lens. A friend has suggested
> that they could actually use an LCD shutter, with concentric rings
> set to transparent or opaque, to get an actual physical-size thing
> going, with real DOF.
> I confess I've not tried any actual tests to see for myself, but maybe
> there's a discussion here while I'm getting around to it...
>
> Armando


Same in digital as in silver based cameras. There is one trick however.
Just as 35mm had the half frame, digital has various sized sensors. So you
will get a little more DOF with the typical digital using a 1.6 factor
sensor (that is the sensor is 1/1.6 the area of a film camera, a little
larger than half frame 35mm silver-film camera.

--
Joseph Meehan

Dia duit


 
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Lorem Ipsum
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Posts: n/a
 
      11-18-2005
"Armando" <(E-Mail Removed)> wrote in message
news:RNcff.2846$(E-Mail Removed)...
> Apologies if this is a rehash, I searched on all the related terms I could
> think of first...
>
> In a "real" camera (sorry about that), the f-stop setting of the lens
> affects the DOF because of the physical size of the aperture. How is
> "f-stop" handled on a digital camera? My guess has always been that it's
> just a electrical tweak to the overall brightness of the image, and not an
> actual "sphincter" in the lens. A friend has suggested that they could
> actually use an LCD shutter, with concentric rings set to transparent or
> opaque, to get an actual physical-size thing going, with real DOF.


Digital cameras use real physical aperture/diaphragms, just like 'real'
cameras.


 
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Dr. Joel M. Hoffman
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      11-18-2005
>In a "real" camera (sorry about that), the f-stop setting of the lens
>affects the DOF because of the physical size of the aperture. How is
>"f-stop" handled on a digital camera? My guess has always been that it's
>just a electrical tweak to the overall brightness of the image, and not an
>actual "sphincter" in the lens. A friend has suggested that they could
>actually use an LCD shutter, with concentric rings set to transparent or
>opaque, to get an actual physical-size thing going, with real DOF.


It depends which kind of camera you have. Certainly dSLR cameras use
a real aperture. I believe that any camera that lets you set the
aperture has a real aperture and it's not simply a computer trick, but
I suppose someone might have manufactured a camera with a
pseudo-aperture.

What kind of camera do you have?

The shutter is a different matter. Many digicams don't have a real
shutter that opens and closes.

-Joel

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Shawn Hirn
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      11-18-2005
In article <RNcff.2846$(E-Mail Removed)>,
"Armando" <(E-Mail Removed)> wrote:

> Apologies if this is a rehash, I searched on all the related terms I could
> think of first...
>
> In a "real" camera (sorry about that), the f-stop setting of the lens
> affects the DOF because of the physical size of the aperture. How is
> "f-stop" handled on a digital camera? My guess has always been that it's
> just a electrical tweak to the overall brightness of the image, and not an
> actual "sphincter" in the lens. A friend has suggested that they could
> actually use an LCD shutter, with concentric rings set to transparent or
> opaque, to get an actual physical-size thing going, with real DOF.


Its the same concept regardless of the type of recording medium, except
that the depth of field range is different than 35mm film cameras
because of the different size ccd area. The principles of optics (which
depth of field relies upon) do not change just because one replaces film
with a CCD.
 
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=?iso-8859-1?q?M=E5ns_Rullg=E5rd?=
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Posts: n/a
 
      11-18-2005
Shawn Hirn <(E-Mail Removed)> writes:

> In article <RNcff.2846$(E-Mail Removed)>,
> "Armando" <(E-Mail Removed)> wrote:
>
>> Apologies if this is a rehash, I searched on all the related terms I could
>> think of first...
>>
>> In a "real" camera (sorry about that), the f-stop setting of the lens
>> affects the DOF because of the physical size of the aperture. How is
>> "f-stop" handled on a digital camera? My guess has always been that it's
>> just a electrical tweak to the overall brightness of the image, and not an
>> actual "sphincter" in the lens. A friend has suggested that they could
>> actually use an LCD shutter, with concentric rings set to transparent or
>> opaque, to get an actual physical-size thing going, with real DOF.

>
> Its the same concept regardless of the type of recording medium, except
> that the depth of field range is different than 35mm film cameras
> because of the different size ccd area. The principles of optics (which
> depth of field relies upon) do not change just because one replaces film
> with a CCD.


Are you not contradicting yourself there?

Depth of field at a given distance is determined by three parameters:
focal length, aperture, and circle of confusion. The first two are
determined by the optics. The circle of confusion is a somewhat
subjective property, and is a function of the required sharpness in
the final image and the size of the recording medium. The image is
perfectly focused only at one exact distance. The depth of field is
the range in which the focal blur is too small to be perceptible.

A neat DoF calculator is available at http://dofmaster.com/dofjs.html.

--
Måns Rullgård
http://www.velocityreviews.com/forums/(E-Mail Removed)
 
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=?iso-8859-1?q?M=E5ns_Rullg=E5rd?=
Guest
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      11-18-2005
Måns Rullgård <(E-Mail Removed)> writes:

> Shawn Hirn <(E-Mail Removed)> writes:
>
>> In article <RNcff.2846$(E-Mail Removed)>,
>> "Armando" <(E-Mail Removed)> wrote:
>>
>>> Apologies if this is a rehash, I searched on all the related terms I could
>>> think of first...
>>>
>>> In a "real" camera (sorry about that), the f-stop setting of the lens
>>> affects the DOF because of the physical size of the aperture. How is
>>> "f-stop" handled on a digital camera? My guess has always been that it's
>>> just a electrical tweak to the overall brightness of the image, and not an
>>> actual "sphincter" in the lens. A friend has suggested that they could
>>> actually use an LCD shutter, with concentric rings set to transparent or
>>> opaque, to get an actual physical-size thing going, with real DOF.

>>
>> Its the same concept regardless of the type of recording medium, except
>> that the depth of field range is different than 35mm film cameras
>> because of the different size ccd area. The principles of optics (which
>> depth of field relies upon) do not change just because one replaces film
>> with a CCD.

>
> Are you not contradicting yourself there?


Sorry, you're not.

--
Måns Rullgård
(E-Mail Removed)
 
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Joseph Meehan
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Posts: n/a
 
      11-18-2005
Måns Rullgård wrote:
> Shawn Hirn <(E-Mail Removed)> writes:
>
>> In article <RNcff.2846$(E-Mail Removed)>,
>> "Armando" <(E-Mail Removed)> wrote:
>>
>>> Apologies if this is a rehash, I searched on all the related terms
>>> I could think of first...
>>>
>>> In a "real" camera (sorry about that), the f-stop setting of the
>>> lens affects the DOF because of the physical size of the aperture.
>>> How is "f-stop" handled on a digital camera? My guess has always
>>> been that it's just a electrical tweak to the overall brightness of
>>> the image, and not an actual "sphincter" in the lens. A friend has
>>> suggested that they could actually use an LCD shutter, with
>>> concentric rings set to transparent or opaque, to get an actual
>>> physical-size thing going, with real DOF.

>>
>> Its the same concept regardless of the type of recording medium,
>> except that the depth of field range is different than 35mm film
>> cameras because of the different size ccd area. The principles of
>> optics (which depth of field relies upon) do not change just because
>> one replaces film with a CCD.

>
> Are you not contradicting yourself there?
>
> Depth of field at a given distance is determined by three parameters:
> focal length, aperture, and circle of confusion.


I don't think he is contradicting himself. Generally we compare the DOF
of two photographs of the same subject. Most digital cameras have a smaller
recording area than a 35mm so to capture the same subject at the same
distance the focal length must be changed. In a typical situation you would
be comparing images from a 35mm with a 50mm lens and a digital with a 32 mm
lens.

> The first two are
> determined by the optics. The circle of confusion is a somewhat
> subjective property, and is a function of the required sharpness in
> the final image and the size of the recording medium. The image is
> perfectly focused only at one exact distance. The depth of field is
> the range in which the focal blur is too small to be perceptible.
>
> A neat DoF calculator is available at http://dofmaster.com/dofjs.html.


--
Joseph Meehan

Dia duit


 
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