Lens musings - Prosumer vs. dSLR

Tul · Dec 29, 2003

Having read much about how prosumer cams have advantages of small fast lenses, but very long DOF, I sat down and made a few calculations on the topic, this is my conclusion:

While the speed of the lens does limit the DOF, there is no advantage in lens speed/size. A 10D with a lens stopped to, say, f/4.9 will be exactly as sensitive as a sony F-717 at f/2.0, and with the same DOF. (at same capture angle)

Because the 717 sensor is smaller it gathers less light and needs a faster lens, with a shorter focal length. A 10D with a larger sensor can capture the exact same light using a slower lens with a longer focal length, which gives exactly the same DOF.

Makes sense to anyone?

Richard Katris · Dec 29, 2003

so how do you get shallow DOF similar to 1.8 on the Canon (cheap 50mm 1.8 is perfect portrait 80mm equivalent on the 1.6 cameras)....on the Sony? You can't also how do you get 400 iso at 1.8 eqivalent on Sony? Motion and shutter speeds will be much slower, and motion more evident even with 2.0 aperature as iso noise is so much higher with smaller sensor.
--
Richard Katris aka Chanan

Tul · Dec 29, 2003

Richard Katris said:
so how do you get shallow DOF similar to 1.8 on the Canon (cheap
50mm 1.8 is perfect portrait 80mm equivalent on the 1.6
cameras)....on the Sony? You can't

Exactly.

Richard Katris said:
also how do you get 400 iso at
1.8 eqivalent on Sony? Motion and shutter speeds will be much
slower, and motion more evident even with 2.0 aperature as iso
noise is so much higher with smaller sensor.
--
Richard Katris aka Chanan

Yup, if both lenses were at f/2.0, the Sony would have much longer shutter speed, about 6x slower, but the Sony would have much greater DOF. Noise in smaller sensors is another matter entirely.

taylor-design · Dec 29, 2003

Tul said:
While the speed of the lens does limit the DOF, there is no
advantage in lens speed/size. A 10D with a lens stopped to, say,
f/4.9 will be exactly as sensitive as a sony F-717 at f/2.0, and
with the same DOF. (at same capture angle)
Because the 717 sensor is smaller it gathers less light and needs a
faster lens, with a shorter focal length.

It's not that the Sony sensor gathers less light, it's that it has a lower signal to noise ratio, hence it is more noisy at a given ISO.

My 70-200 f/4 is 1 stop slower than the Sony lens in Reichman's review that everyone is flipping out about. BUT my 10D has less noise at ISO 400 than the Sony at ISO 100. In the end I have a 1 stop advantage plus better DoF control and more stops of light cutting ability (> f/8) for brighter shots when I, for some reason, want slower shutter speeds.

Tul · Dec 29, 2003

taylor-design said:
It's not that the Sony sensor gathers less light, it's that it has
a lower signal to noise ratio, hence it is more noisy at a given
ISO.

My 70-200 f/4 is 1 stop slower than the Sony lens in Reichman's
review that everyone is flipping out about. BUT my 10D has less
noise at ISO 400 than the Sony at ISO 100. In the end I have a 1
stop advantage plus better DoF control and more stops of light
cutting ability (> f/8) for brighter shots when I, for some reason,
want slower shutter speeds.

Wrong. Sure you have less noise because of a larger sensor, but much more light will also hit the sensor, meaning more light for each pixel. So the Sony sensor will gather less light, as the sensor area is only 1/6 of the Canons.

Nabal · Dec 29, 2003

Tul said:
While the speed of the lens does limit the DOF, there is no
advantage in lens speed/size. A 10D with a lens stopped to, say,
f/4.9 will be exactly as sensitive as a sony F-717 at f/2.0, and
with the same DOF. (at same capture angle)

I'm having difficulty following you.

Let's say I prefer to use a hand-held, incident light meter and set the shutter speed and lens aperture on my camera manually. On the hand-held meter I set the ISO to 100, press the button and take a reading, and the readout says the correct exposure is f/5.6 lens aperture and 1/125th second shutter speed.

Are these the correct lens aperture and shutter speed settings for the Sony F-717 or the Canon 10D?

Gene Windell

Tul · Dec 30, 2003

Ah, but that's a different thing really. The reading will be correct for both, as ISO 100 will mean same sensitivity for entire sensor. It also means that the sony will amplify noise much more to get that sensitivity.

Gene Windell said:
Tul said:

While the speed of the lens does limit the DOF, there is no
advantage in lens speed/size. A 10D with a lens stopped to, say,
f/4.9 will be exactly as sensitive as a sony F-717 at f/2.0, and
with the same DOF. (at same capture angle)

Click to expand...

I'm having difficulty following you.

Let's say I prefer to use a hand-held, incident light meter and set
the shutter speed and lens aperture on my camera manually. On the
hand-held meter I set the ISO to 100, press the button and take a
reading, and the readout says the correct exposure is f/5.6 lens
aperture and 1/125th second shutter speed.

Are these the correct lens aperture and shutter speed settings for
the Sony F-717 or the Canon 10D?

Gene Windell

Godfrey · Dec 30, 2003

This is incorrect.

Using both a Canon 10D and a Sony F717

pick a scene and set both cameras, at the same distance, with the same framing on the scene.
set ISO 100
set the same f/stop and shutter speed

The results will have the same densities and exposure. The difference is that the Sony will have more depth of field. If you got the exposure correct, the Sony will have a bit more noise than the Canon. If you underexposed, the Sony will have a lot more noise.

The Canon's great advantages are interchangeable, high quality lenses and the ability to obtain low noise images at higher ISO ratings, the ability to obtain a shallower depth of field at wide aperture settings with similar framing and perspective scenes.

The Sony's great advantages are a wide-range, fast zoom lens of high quality coupled with great depth of field in a smaller, lighter, handier package, along with the swivel body and other feature designs that can only be executed with an all-digital camera (like live image preview, fast IR shooting, etc).

Both cameras have their limitations as well. I moved to the Canon for some of its advantages that are well suited to my shooting needs, but miss some of the Sony F717's advantages that I'd grown accustomed to. The Canon is a less limited camera in most ways than the Sony but at a much greater cost in dollars, size and weight.

Godfrey

Tul said:
... Yup, if both lenses were at f/2.0, the Sony would have much longer
shutter speed, about 6x slower, but the Sony would have much
greater DOF. Noise in smaller sensors is another matter entirely.

Godfrey · Dec 30, 2003

Tul,

f/4 will pass the same amount of energy (light) in unit time through both the Sony and the Canon lens.

Godfrey

Tul said:
Gene Windell said:

Tul said:

While the speed of the lens does limit the DOF, there is no
advantage in lens speed/size. A 10D with a lens stopped to, say,
f/4.9 will be exactly as sensitive as a sony F-717 at f/2.0, and
with the same DOF. (at same capture angle)

Click to expand...

I'm having difficulty following you.

Let's say I prefer to use a hand-held, incident light meter and set
the shutter speed and lens aperture on my camera manually. On the
hand-held meter I set the ISO to 100, press the button and take a
reading, and the readout says the correct exposure is f/5.6 lens
aperture and 1/125th second shutter speed.

Are these the correct lens aperture and shutter speed settings for
the Sony F-717 or the Canon 10D?

Gene Windell

Click to expand...

Jason Hutchinson · Dec 30, 2003

Godfrey said:
Tul,

f/4 will pass the same amount of energy (light) in unit time
through both the Sony and the Canon lens.

The energy passed through the lens is the greater because the area of the image (at the same power) is greater. Energy is the integral of power over time (and in this case 2D space), and therefore will be greater with the Canon setup. This is the whole point of a large sensor... there is more energy to capture. If you said the even energy per unit area was the same at the same aperture I'd agree, since that's the whole purpose of aperture.

Jason

Godfrey · Dec 30, 2003

Well, I'm not a physics major; perhaps I spoke imprecisely. But what I meant to say was that f/4@ will produce the same image brightness in both cameras at a given ISO.

The fact that the Canon's sensor is larger and collects more energy to work with is what allows it to have lower noise, but the difference is going to be noise level at a particular ISO setting, not that the Sony is going to require more or less exposure than the Canon to achieve a proper exposure.

Godfrey

Jason Hutchinson said:
Godfrey said:

Tul,

f/4 will pass the same amount of energy (light) in unit time
through both the Sony and the Canon lens.

Click to expand...

The energy passed through the lens is the greater because the area
of the image (at the same power) is greater. Energy is the
integral of power over time (and in this case 2D space), and
therefore will be greater with the Canon setup. This is the whole
point of a large sensor... there is more energy to capture. If you
said the even energy per unit area was the same at the same
aperture I'd agree, since that's the whole purpose of aperture.

Jason

Tul · Dec 30, 2003

Hehe, I think we all agree more or less....

When using a certain ISO and f-number, exposures will be the same time, but the 717-sensor will have 6 times higher gain to achieve the ISO than the 10D sensor, because of the sensor size difference. This leads to noise.

In my initial musings I was not considering sensor gain at all, it was more a thought on DOF and lens speed...

Some people think that to equal a 717 lens on a 10D you'd need a 24-120mm f/2.0-2.4, but this is not true. A 24-120 f/5 would be more like it.

Godfrey said:
The fact that the Canon's sensor is larger and collects more energy
to work with is what allows it to have lower noise, but the
difference is going to be noise level at a particular ISO setting,
not that the Sony is going to require more or less exposure than
the Canon to achieve a proper exposure.

Godfrey

Jason Hutchinson said:

Godfrey said:

Tul,

f/4 will pass the same amount of energy (light) in unit time
through both the Sony and the Canon lens.

Click to expand...

The energy passed through the lens is the greater because the area
of the image (at the same power) is greater. Energy is the
integral of power over time (and in this case 2D space), and
therefore will be greater with the Canon setup. This is the whole
point of a large sensor... there is more energy to capture. If you
said the even energy per unit area was the same at the same
aperture I'd agree, since that's the whole purpose of aperture.

Jason

Click to expand...

dnjake · Dec 30, 2003

taylor-design said:
It's not that the Sony sensor gathers less light, it's that it has
a lower signal to noise ratio, hence it is more noisy at a given
ISO.

There is less signal because there is less light. The cheap Sony lens is possible because it is smaller. Because it is smaller, it gathers less light.
--
David Jacobson

Godfrey · Dec 30, 2003

Why do you say that? An f/5 maximum aperture would restrict the photographer's ability to shoot in low light much much more than the Sony's f/2-2.4. There's no equivalence there, other than for DoF control.

There's no real need to keep hashing this around. If there weren't some advantage to a large sensor, much more expensive camera, no one would be interested in them.

Godfrey

Tul said:
...Some people think that to equal a 717 lens on a 10D you'd need a
24-120mm f/2.0-2.4, but this is not true. A 24-120 f/5 would be
more like it.

Jason Hutchinson · Dec 30, 2003

Godfrey said:
There's no real need to keep hashing this around. If there weren't
some advantage to a large sensor, much more expensive camera, no
one would be interested in them.

Godfrey

Tul said:

...Some people think that to equal a 717 lens on a 10D you'd need a
24-120mm f/2.0-2.4, but this is not true. A 24-120 f/5 would be
more like it.

Click to expand...

taylor-design · Dec 30, 2003

Tul said:
Wrong. Sure you have less noise because of a larger sensor, but
much more light will also hit the sensor, meaning more light for
each pixel. So the Sony sensor will gather less light, as the
sensor area is only 1/6 of the Canons.

Perhaps I should clarify.

f/2.8 is f/2.8 REGARDLESS of the lens. A smaller lens is mated to a smaller sensor or piece of film, hence the EV value at the surface of the sensor remains the same.

Yes, the 10D sensor has more area, and yes, that's related to S/N. But the EV is the same for a given area of sensor real estate. If through some technology the Sony sensor achieved as high a S/N as the 10D sensor, then the Sony would have a 1 stop advantage (over my 70-200 f/4) regardless of how much total light was hiting my 10D sensor.

The future may bring such technology, but right now sensor size is related directly to S/N.

taylor-design · Dec 30, 2003

dnjake said:
taylor-design said:

It's not that the Sony sensor gathers less light, it's that it has
a lower signal to noise ratio, hence it is more noisy at a given
ISO.

Click to expand...

There is less signal because there is less light. The cheap Sony
lens is possible because it is smaller. Because it is smaller, it
gathers less light.
--
David Jacobson

James Barrett · Dec 30, 2003

I thought that aperature was actually a fraction of focal length. (i.e. f5 is actually 1/5th the focal length). This means that with both lenses at f2.0, each lens is gathering 1/2 the light that it is physically able to collect at each given focal length

If this is true, then what both of you say is true. the sony's lens at 2.0 will not gather as much light as a canon lens at 2.0 because it does not need to (nor is it physically able to).

Jason Hutchinson said:
Godfrey said:

There's no real need to keep hashing this around. If there weren't
some advantage to a large sensor, much more expensive camera, no
one would be interested in them.

Godfrey

Tul said:

...Some people think that to equal a 717 lens on a 10D you'd need a
24-120mm f/2.0-2.4, but this is not true. A 24-120 f/5 would be
more like it.

Click to expand...

Click to expand...

--

There was none in the bed and the little one said 'roll-over, roll-over!' So they all rolled over and one fell out, -1 in the bed and the little one said......

Tom Crowning · Dec 30, 2003

The magic words are light per square mm. If the sensor area has half the size you need half the lens opening to get the same sensitivity.
Regards,
tc

Tul said:
Having read much about how prosumer cams have advantages of small
fast lenses, but very long DOF, I sat down and made a few
calculations on the topic, this is my conclusion:

While the speed of the lens does limit the DOF, there is no
advantage in lens speed/size. A 10D with a lens stopped to, say,
f/4.9 will be exactly as sensitive as a sony F-717 at f/2.0, and
with the same DOF. (at same capture angle)
Because the 717 sensor is smaller it gathers less light and needs a
faster lens, with a shorter focal length. A 10D with a larger
sensor can capture the exact same light using a slower lens with a
longer focal length, which gives exactly the same DOF.

Makes sense to anyone?

--
Some digital cameras, some lenses, 2 eyes

http://www.tom-crowning.com

Jason Hutchinson · Dec 30, 2003

James Barrett said:
I thought that aperature was actually a fraction of focal length.
(i.e. f5 is actually 1/5th the focal length).
This means that with
both lenses at f2.0, each lens is gathering 1/2 the light that it
is physically able to collect at each given focal length

You basically had it up until the 1/2 stuff. An f/2 lens collects 1/2 the light of an f/1.4 lens, or 1/4 the light of a 1.0 lens, or 1/8th the light of an f/.7 lens etc...

James Barrett said:
If this is true, then what both of you say is true. the sony's lens
at 2.0 will not gather as much light as a canon lens at 2.0 because
it does not need to (nor is it physically able to).

That's the general idea. What confuses some people is this is already inherently "factored in" in the increased ISOs of the larger medium, so in general you can look at merely the aperture independent of how much energy is collected. On the other hand, you could look at the increased energy delivered to the sensor over an exposure instead, but this is just another way of looking at the increased ISOs, not an additional benefit beyond the ISOs.

Jason

Jason

Lens musings - Prosumer vs. dSLR

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