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Aperture and sensor size?

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Sarah J Connor

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I have a question for those who had considered this question and if you can answer them I would appreciated very much. With dp1 maximum aperture f4, I wonder what this will equal to in term of compact with smaller sensor, for example f1.4? f2.0? f2.8?. The reason I ask is with my limited understanding that the aperture size of sensor (area) that capture light does relative to amount of light that hit the sensor. Thus the larger area, the less amount of needing to open up and like wise the smaller area needs to open up more to allow the light to hit the sensor? I would like to see more hard number than just some pull from the hat speculation. I know some of you here are very bright.
Thank you!
--
Sarah (no relation to terminator's Sarah)
 
Sarah,

I cannot give you a definitive reply, but I think I saw a post in the past day - don't recall where - which may relate to your question.

In terms of light gathering efficiency, I think f4 is f4 is f4. We normally think of this as the working aperture of the front element vs. the focal length. A separate issue which I think has to do with the characteristics of the light path from lens to the sensor is the physical size of the "aperture" (which I think refered in the other thread to the exit pupil of the lens). As I understand it that can vary (and should) depending upon sensor size and characteristics.

Hopefully others more conversant can either correct me or flesh this out.

Kind regards,
--
Ed_S
http://www.pbase.com/ecsquires
 
In terms of light gathering capability, f4.0 is equivalent to f4.0 irrespective of the sensor size.

That said, usually a larger sensor can be pushed to higher ISO values with acceptable loss of Image Quality compared to a smaller one.

Foveon's X3 technology is not really the best one for low light/high ISO, so I tend to consider it as having only about 2 stops advantage over the small sensors used in other compact digicams.

While I consider a modern big CMOS sensor having a good 4 stops advantage over tyny compact sensors.

Of course in good light other factors need to be considered, and the X3 sensor really shines.

Others may disagree of course.

--
Ian Gianni
 
Francesco Gianni said:
In terms of light gathering capability, f4.0 is equivalent to f4.0
irrespective of the sensor size.
Click to expand...
This is a misunderstanding.

The light gathering is not defined by the F-stop. An astronomical telescope of the larger kind has enormous light gathering capability - but the lens might be F10.

The light intensity in the sensor plane is the same for lenses with the same F-stop though.

The light gathering capacity is proportional to area of the sensor divided with the square of the F-stop.

So, Sarah is right.

--
Roland
 
Roland Karlsson said:
Francesco Gianni said:
In terms of light gathering capability, f4.0 is equivalent to f4.0
irrespective of the sensor size.
Click to expand...
This is a misunderstanding.

The light gathering is not defined by the F-stop. An astronomical
telescope of the larger kind has enormous light gathering capability
  • but the lens might be F10.
The light intensity in the sensor plane is the same for lenses with
the same F-stop though.

The light gathering capacity is proportional to area of the sensor
divided with the square of the F-stop.

So, Sarah is right.

--
Roland
Click to expand...
Hi, Roland,

Forgive me - although I once had a rudimentary understanding of optical physics, I'm not sure I'm getting your/Sarah's point. I assumed we were talking about the "working numbers" for want of a better term.

My understanding of the question was whether any (prime) f 4 lens (subject to its design efficiency) would deliver a similar/predictable amount of illumination at the sensor. And, therefore, would a given lens of a given f number and focal length provide "more" or "less" light at the sensor depending upon the sensor area.

I perhaps misspoke about light gathering in the general sense as a larger lens or mirror imaging system would presumably gather more total light than a smaller one of the same number - if I get your point.

Clarification welcome.

Kind regards,
--
Ed_S
http://www.pbase.com/ecsquires
 
Ed_S said:
Hi, Roland,

Forgive me - although I once had a rudimentary understanding of
optical physics, I'm not sure I'm getting your/Sarah's point. I
assumed we were talking about the "working numbers" for want of a
better term.
Click to expand...
Sarah was asking about the "amount of light that hit the sensor".

And - "amount" - can be interpreted in many ways of course.

I interpreted "amount" as the amount of light that the entire sensor collects at a given time - or per time unit - if you so like.

Then - the larger sensor will collect more light at the same F-stop.

But - if you mean "amount" of light per time unit and area unit, i,e, light intensity - then you are of course right.

--
Roland
 
Truman Prevatt said:
The very reason the exposure given by your hand held light meter will
determine the same exposure settings on a 4x5 or P&S.
Click to expand...
Yeah - but the larger area of the 4x5 will give you either higher ISO or more resolution - your choice.

And thats the result of the larger area collecting more photons per time unit at the same F-stop.

--
Roland
 
Roland Karlsson said:
Yeah - but the larger area of the 4x5 will give you either higher ISO
or more resolution - your choice.

And thats the result of the larger area collecting more photons per
time unit at the same F-stop.

--
Roland
Click to expand...
I don't get it. Higher ISO? An f-stop is an f-stop. If I take a measurement with a light meter, I can apply those settings (aperture and shutter speed) to any format of camera. All other things being equal the meter gives me the correct exposure for a P&S, 35mm, 4x5, whatever. In fact, at the larger sizes (4x5) the film would act more like it was half the actual ISO due to resiprocity failiure, due to the rear element of the lens being so far away from the surface of the film, resulting in the need to open up the lens a bit or increase exposure time.

The f-stop is relative. The f number is calculated by taking the focal length and dividing it by the diameter of the aperture, or something like that. So the short answer to what I think Susan was asking is: No, the lens on the DP1 is not faster at f4 because it is smaller. f4 on th e DP1 lens is not equal to 2.8 on a larger camera. The DP1 at f4 will not produce the same exposure as another camera at f2.8.
Hope that helps.
 
The maths is simple.

The f number is the focal length of the lens divided by the diameter of the aperture.

So for the 16.6 mm lens on the DP-1, the aperture is 4.15 mm wide fully open.

On typical P&S camera with a 6 mm lens, f/4 is an aperture 1.5 mm wide. Similarly an aperture the same size as that of the DP-1 would be equivalent to a f/1.4

As the focal length gets smaller as the sensor gets smaller (for a given angle of view) and the physical size of any particular f stop gets smaller in proportion.

More light has to enter the lens for the bigger sensor, but that light is spread over a greater area, so the exposure remains the same for any given f stop.

--
Thanks,
Gary.
 
I am not sure if this is an attempt at insult or compliment? Is the pararise too idylly? must be the lava perhap? or the goat ate your cameras?
rick decker said:
I think you know more than you are letting on Sarah.. In fact, I
think you are "Sneaky, Provocative, and Manipulative", IMHO.
--
It's a tough job living in Hawaii but somebody's got to do it.

See Sigma Lens Tests At:
http://www.lightreflection.com/sigmalenstests/matrix.htm



http://www.lightreflection.com
http://www.silveroaksranch.com
http://www.pbase.com/rickdecker
Click to expand...
--
Sarah (no relation to terminator's Sarah)
 
Better check you physics. At f4 on any lens you will get the same light energy per area. On a sensor with the same ISO you will get the same exposure. Has nothing to do with resolution. Has noting to do with ISO.

A photograph is about the light per unit area captured - not the total light energy captures. Sure you capture more total light energy on an 8x10 sheet of film than you do on an ASP sensor by the ratio of the sensor area. However, for energy per square mm - they are the same.
Roland Karlsson said:
Truman Prevatt said:
The very reason the exposure given by your hand held light meter will
determine the same exposure settings on a 4x5 or P&S.
Click to expand...
Yeah - but the larger area of the 4x5 will give you either higher ISO
or more resolution - your choice.

And thats the result of the larger area collecting more photons per
time unit at the same F-stop.

--
Roland
Click to expand...
--
Truman
http://www.pbase.com/tprevatt

 
As Roland said, you're quite right in your thinking here, Sarah, though few photographers including practising pros understand this well. Roughly speaking, to get a similar depth of field from two cameras with different sensor sizes, with lenses of equivalent angle of view, the apertures (or entrance pupils, to be more accurate) must be of equal diameter. This would also deliver the same amount of light to the sensors, resulting in equal noise performance if all other factors are identical (which they never are, with smaller sensors often performing better than expected).

The DP1 has a lens of 16.6 mm focal length and minimum f-stop 4. The maximum aperture is therefore 16.6 / 4 = 4.15 mm.

The DP1's sensor size is 20.7 x 13.8 mm, while a 1/1.7" sensor (as used in the Canon G9, for example), is 7.60 x 5.70 mm, or about 2.6 times shorter in the diagonal. So a 28 mm-equivalent lens on such a sensor would require a focal length of 6.3 mm. And for a 6.3 mm lens to have a maximum aperture of 4.15 mm would require a minimum f-stop of f/1.5.

If the sensor were 1/2.5", another common size, the lens would have to open up to fully f/1.2 to get comparable depth of field and photon throughput as the DP1's f/4 lens.

Obviously no compact digital cameras with such lenses exist, which is why the DP1 has better low light performance than any compact camera with a small sensor, despite having a slower lens than most of them.
 
Thank you so much for explaining it fully, as I can never put it together as explicit or eloquently.
Philidors shadow said:
As Roland said, you're quite right in your thinking here, Sarah,
though few photographers including practising pros understand this
well. Roughly speaking, to get a similar depth of field from two
cameras with different sensor sizes, with lenses of equivalent angle
of view, the apertures (or entrance pupils, to be more accurate) must
be of equal diameter. This would also deliver the same amount of
light to the sensors, resulting in equal noise performance if all
other factors are identical (which they never are, with smaller
sensors often performing better than expected).

The DP1 has a lens of 16.6 mm focal length and minimum f-stop 4. The
maximum aperture is therefore 16.6 / 4 = 4.15 mm.

The DP1's sensor size is 20.7 x 13.8 mm, while a 1/1.7" sensor (as
used in the Canon G9, for example), is 7.60 x 5.70 mm, or about 2.6
times shorter in the diagonal. So a 28 mm-equivalent lens on such a
sensor would require a focal length of 6.3 mm. And for a 6.3 mm lens
to have a maximum aperture of 4.15 mm would require a minimum f-stop
of f/1.5.

If the sensor were 1/2.5", another common size, the lens would have
to open up to fully f/1.2 to get comparable depth of field and photon
throughput as the DP1's f/4 lens.

Obviously no compact digital cameras with such lenses exist, which is
why the DP1 has better low light performance than any compact camera
with a small sensor, despite having a slower lens than most of them.
Click to expand...
--
Sarah (no relation to terminator's Sarah)
 
Philidors shadow wrote:
(...)
Philidors shadow said:
Obviously no compact digital cameras with such lenses exist, which is
why the DP1 has better low light performance than any compact camera
with a small sensor, despite having a slower lens than most of them.
Click to expand...
So you are saying that, under a given lightning condition, a 2/3" sensor at F4 and 28mm equiv. lens needs longer exposure time than the X3 sensor at F4 and a 28mm equiv.lens?

I somehow doubt this.

O.
--
http://www.flickr.com/photos/ollivr/
http://www.flickriver.com/photos/ollivr/popular-interesting/
 
Tiffles said:
light_reaction said:
Obviously no compact digital cameras with such lenses exist, which is
why the DP1 has better low light performance than any compact camera
with a small sensor, despite having a slower lens than most of them.
Click to expand...
So you are saying that, under a given lightning condition, a 2/3"
sensor at F4 and 28mm equiv. lens needs longer exposure time than the
X3 sensor at F4 and a 28mm equiv.lens?

I somehow doubt this.
Click to expand...
and see if you have more question.
light_reaction said:
O.
--
http://www.flickr.com/photos/ollivr/
http://www.flickriver.com/photos/ollivr/popular-interesting/
Click to expand...
--
Sarah (no relation to terminator's Sarah)
 
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