Are apertures on DLSR's comparable to apertures on P&S cameras?

[David B Burnette]

I currently own a P&S and I'm looking to improve low light peformance, and am considering whether my best option would be a Panasonic LX3 (the best P&S option) or going DSLR (on a budget!) with an entry level kit like the Canon 1000D.

I have discussed in another thread various body and lens DSLR option, but my question here is about calculating how many stops difference in low light performance I would get between both options.

I worked it out as follows:

Aperture:
LX3 is f/2.0 at its widest
1000D kit lens is f/3.5 at its widest
=> about 1.5 stops advantage to the LX3

ISO Performance:
LX3 ISO400 is about the same as 1000D at ISO1600
=> about 2 stops advantage to the 1000D
(you may disagree here - but let's just run with that for the sake of argument)

This means that I would get around 0.5 stops advantage going with the 1000D with its kit lens, which is not much.

However, I have seen a couple of posts where users say that the apertures of P&S cameras and DSLR cameras aren't comparable because of the different sensor sizes, and claiming that f/4.0 on a DLSR is actually no slower than f/2.8 on a P&S.

In one such post the poster says that at a given aperture and ISO, there DSLR achieved a shutter speed of around 1.5 stops faster than their P&S. However, when I look at image samples from Imaging Resource and dpReview, in comparing EXIF data of a few P&S and DSLR images the exposures are pretty much the same.

I'm not sure how to make sense of this. I'd appreciate any advice to help clarify my estimate above of how many stops improvement I could expect from a 1000D kit over an LX3.

 

[jpmalohesr]

I currently own a P&S and I'm looking to improve low light
peformance, and am considering whether my best option would be a
Panasonic LX3 (the best P&S option) or going DSLR (on a budget!) with
an entry level kit like the Canon 1000D.

I have discussed in another thread various body and lens DSLR option,
but my question here is about calculating how many stops difference
in low light performance I would get between both options.

I worked it out as follows:

Aperture:
LX3 is f/2.0 at its widest
1000D kit lens is f/3.5 at its widest
=> about 1.5 stops advantage to the LX3

ISO Performance:
LX3 ISO400 is about the same as 1000D at ISO1600
=> about 2 stops advantage to the 1000D
(you may disagree here - but let's just run with that for the sake of
argument)

This means that I would get around 0.5 stops advantage going with the
1000D with its kit lens, which is not much.

However, I have seen a couple of posts where users say that the
apertures of P&S cameras and DSLR cameras aren't comparable because
of the different sensor sizes, and claiming that f/4.0 on a DLSR is
actually no slower than f/2.8 on a P&S.

I don't believe this is true. With everything else equal, f4 is f4 regardless of camera.

In one such post the poster says that at a given aperture and ISO,
there DSLR achieved a shutter speed of around 1.5 stops faster than
their P&S. However, when I look at image samples from Imaging
Resource and dpReview, in comparing EXIF data of a few P&S and DSLR
images the exposures are pretty much the same.

I'm not sure how to make sense of this. I'd appreciate any advice to
help clarify my estimate above of how many stops improvement I could
expect from a 1000D kit over an LX3.

I am curious as to what answers you are going to get here.

 

[Christakis]

Well I am not an expert but here I go:
Yes and No.

I assume you know the aperture / shutter speed compromise. Higher f stop requires more shutter speed and vice versa. Keep that in mind and now think of the aperture / DOF compromise.

The higher the DOF you want the higher the aperture you need. BUT when you have a smaller sensor you get more DOF for free.

So yes in terms of light f2 on P&S and f2 on SLR is the same.

However, in terms of DOF, P&S would give you more DOF than what an SLR would (for the same aperture that is). Which means in order to get the same DOF using an SLR you would need to increase the aperture a tad (which unfortunately would also mean more shutter speed)

--
Christakis
http://www.pbase.com/christakis/

 

[karoberts]

I did a quick search, and found this site

http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm

They have a little calculator on there where you can enter the sensor size/focal length/aperture and then compare to a different sensor size

I tried with this info
1.6X crop
F4
18mm (kit lens widest)

compared to

digital compact with 1/1.8" (LX3 is 1/1.63")

Which resulted in the LX3 needing a 7mm focal length and an F1.6 aperture (to get the same perspective and depth-of-field

I however don't know if an LX3 at F2.0 gets more light than the kit lens on a 1000D at F4. I would be very interested to know the answer to that question.

 

[Weth]

Exposures should be the same, it is not dependent on sensor size.

I would debate your premise that 400 ISO on a the small sensor is equal to 1600 ISO on APS-C sensor in regards to noise characteristics. That is not my experience.

For less than US$100 you can get a 50 mm f/1.8 for the 1000D and you are talking no comparison for low light performance.

 

[tkbslc]

As was mentioned, it is both yes and no. For exposure purposes, it is the same. For DOF control, it is not. If you want blurred background for subject isolation, then the SLR is much better. If you want more DOF to get more of the scene in focus, then the P&S is bettter.

One thing to forget is that you can interchange the lenses on a dSLR, so you can have fast/slow, long/short and everything in between. And a SLR with a f2,8 zoom, or f1.8 prime would have a distinct advantage by having same or faster shutter speeds, and cleaner ISO.

There are more advantages to the SLR than just ISO noise though....

 

[Manehead]

To say f2.8 is the same regardless of sensor size isn't strictly true.

As I understand it, the f-nubmer determines the amount of light per unit area that falls onto the sensor. i.e. every square cm on the P&S sensor will recieve the same amount of light as every square cm on the DSLR sensor.

However, due to the smaller size of the P&S sensor, the photo cells are much densely packed together. This means for each square cm, there are many more photo cells on the P&S than on the DSLR. Therefore, each individual photo cell on the P&S is exposed to much less light than each cell on the DSLR.

To compensate for this reduced light, and to achieve the same exposure as the DSLR, the signal from each photo cell on the P&S needs to be amplified by a greater amount, hence why you will see more noise on a P&S even at low ISOs compared to their bigger brother.

 

[Jim Cassatt]

The f-stop (aperture) is the ratio of the focal length of the lens to the diameter. f2 is f2 regardless of the camera and is a measure of how much light the lens is letting in to hit the sensor.

One thing you did consider: Does your lens or P&S have IS? That would figure into your calculations.

Also as someone has mentioned, you can buy an f1.8 lens for about $90.00. As was also mentioned you have to consider DOF, also focusing ability under low light conditions.

--
Jim
http://www.pbase.com/jcassatt

 

[brightcolours]

Well I am not an expert but here I go:
Yes and No.

I assume you know the aperture / shutter speed compromise. Higher f
stop requires more shutter speed and vice versa. Keep that in mind
and now think of the aperture / DOF compromise.

The higher the DOF you want the higher the aperture you need. BUT
when you have a smaller sensor you get more DOF for free.

So yes in terms of light f2 on P&S and f2 on SLR is the same.

However, in terms of DOF, P&S would give you more DOF than what an
SLR would (for the same aperture that is). Which means in order to
get the same DOF using an SLR you would need to increase the
aperture a tad (which unfortunately would also mean more shutter
speed)

--
Christakis
http://www.pbase.com/christakis/

Shallow DOF is a PRE, not a CON. If you want the snap shot look always, go for a big DOF. If you want to be more creative, be happy and learn to use shallow depth of field creatively.

 

[brightcolours]

f-stops tell how much light gets through, focal length in relation to aperture (hole in lens size).

So... you are correct in the advantage of the LX3 at ISO 100 compared to a DSLR at ISO 100, where the DSLR has a smaller max. aperture.

You are also correct in that the DSLR has a big advantage in ISO performance.

There are two other issues with aperture, though.
Aperture is the hole in the lens... f-stops are focal length / aperture size.

The smaller an aperture is, the more diffraction of the light at the edges of the aperture occurs. Since the focal lengths of the LX3 are a LOT shorter than with a DSLR like the 450D, the apertures are a LOT smaller at equivalent focal lengths with the same f-stop figures. This will mean that diffraction (light "rays" being bent along the edges of the hole, and landing on different parts of the sensor, creating a soft image) will set in a LOT sooner with the compact camera.

Also, the smaller aperture and the much shorter focal length of the compact camera mean that you can not achieve a shallow depth of field.

All in all, the compact point and shoot is at disadvantage with its short focal lengths, small apertures and tiny chips.

 

[GaryW]

David B Burnette wrote:
....

However, I have seen a couple of posts where users say that the
apertures of P&S cameras and DSLR cameras aren't comparable because
of the different sensor sizes, and claiming that f/4.0 on a DLSR is
actually no slower than f/2.8 on a P&S.

In one such post the poster says that at a given aperture and ISO,
there DSLR achieved a shutter speed of around 1.5 stops faster than
their P&S.

Yeah, I think that was me. I decided I needed to do a bit more research, and it seems that the whole "exposure" issue is a distraction. If I understood it correctly, manufacturers set what "ISO 100" means for a particular camera by changing the sensor's amp gain, so "exposure" is really an arbitrary comparison. Sure, you could find one manufacturer's ISO 100 on a P&S to match exactly that of a DSLR's ISO 100, but I don't think that would, in and of itself, make the cameras "equal".

To match the same field-of-view, the small sensor camera has a smaller aperture opening (even if it's the same f-number), thus it lets in less light (than the same aperture number for a larger focal length lens). When light is really good, the P&S camera is probably good enough. It's when light is not so good that the differences will really show. (Although, even in good light, the dynamic range can still make a difference...)

I think you're onto the correct way of looking at it, which is determining the quality (such as the signal to noise ratio) of both cameras at given ISO ratings. If you can make use of the DSLR at ISO 400 and get as good results as ISO 100 on the P&S, then that counteracts the f2.0 advantage to some extent. But you still don't know if ISO 100 is comparable on any given two cameras. Try looking at review sites (DxOmark is interesting).

As someone else mentioned, the aperture defines the amount of light to allow in. I'm sure that I have this wrong, but I'm going to keep going... So to have the same time exposure, you'd have to have the same aperture size to let the same amount of light in. It doesn't matter if the sensor is larger or smaller, if it's the same amount of light, then each pixel captures that light (assuming the same number of pixels on small and large sensors). But now we're talking about a P&S with an f1.2 or something lens compared to a DSLR with an f3.5 just to have the same size aperture opening to have them both capture an equivalent amount of light at the same angle of view. And this is why I think you see the quality difference at the various ISOs, because less light is being used to generate an image on the P&S cameras.

Does that sound right?

It does make it really hard to compare when there are different exposures for the same ISO, though.

I wish the LX3 really were equal to the DSLRs, then I could stop carrying so much bulk around.
--
Gary W.

 

[Christakis]

Aperture is simply a ratio of the focal length vs the "effective" diameter of the lens.

In P&S cameras the focal length is a lot smaller than SLRs so is the width of the lens though, effectively giving the same f stop.

think of it as, big / big = small / small

If im still not clear:
http://en.wikipedia.org/wiki/F-number

--
Christakis
http://www.pbase.com/christakis/

 

[David B Burnette]

However, I have seen a couple of posts where users say that the
apertures of P&S cameras and DSLR cameras aren't comparable because
of the different sensor sizes, and claiming that f/4.0 on a DLSR is
actually no slower than f/2.8 on a P&S.

In one such post the poster says that at a given aperture and ISO,
there DSLR achieved a shutter speed of around 1.5 stops faster than
their P&S.

Yeah, I think that was me. I decided I needed to do a bit more
research, and it seems that the whole "exposure" issue is a
distraction. If I understood it correctly, manufacturers set what
"ISO 100" means for a particular camera by changing the sensor's amp
gain, so "exposure" is really an arbitrary comparison. Sure, you
could find one manufacturer's ISO 100 on a P&S to match exactly that
of a DSLR's ISO 100, but I don't think that would, in and of itself,
make the cameras "equal".

Yes, Gary, it was you responsible for my confusion!

Seriously though, I thought it was worth starting a thread on this issue, as I really wanted to know if the exposures on P&S and DSLR cameras could be directly compared to see how much many stops advantage you got when going to DSLR for low light photography.

I know there are other reasons to go DSLR, such as greater control of DOF, speed etc, but in my case I am just looking at being able to take clean images in challenging light conditions. And from my original assessment of the LX3 and the Canon 1000D with kit lens, the gap between the best P&S and entry-level DSLR seems pretty close.

Just to clarify what I want to achieve, it's mainly photographing my two kids (both toddlers). I find not just for indoor photography, but in the evenings outdoors I'd like to be able to achieve higher shutter speeds without stepping up the ISO on my current P&S so much that noise becomes a real problem.

I currently have a Fuji F100FD, and the LX3 will give me a good 1 stop advantage because of its faster lens. I would find the 60mm reach of the LX3 a restriction, but I find a lot of the time I'm using wider angles in any case so the aperture doesn't close down too much in my F100FD and therefore needing to decrease shutter speed.

The Canon 1000D with kit lens wouldn't seem to me to be much of an improvement over the LX3 - plus having a P&S is a lot more manageable with 2 little kids!

 

[WilbaW]

I know there are other reasons to go DSLR, such as greater control of
DOF, speed etc, but in my case I am just looking at being able to
take clean images in challenging light conditions.

Then you need the largest sensor you can afford - go for the DSLR!

 

[Anastigmat]

I currently own a P&S and I'm looking to improve low light
peformance, and am considering whether my best option would be a
Panasonic LX3 (the best P&S option) or going DSLR (on a budget!) with
an entry level kit like the Canon 1000D.

No contest. Go with the DSLR for best low light performance.

I have discussed in another thread various body and lens DSLR option,
but my question here is about calculating how many stops difference
in low light performance I would get between both options.

I worked it out as follows:

Aperture:
LX3 is f/2.0 at its widest
1000D kit lens is f/3.5 at its widest
=> about 1.5 stops advantage to the LX3

With an SLR, you can buy a 50mm f/1.8 Canon lens for very little money. You can buy an f/1.2 lens for a lot of money. Don't be limited to the kit lens.

ISO Performance:
LX3 ISO400 is about the same as 1000D at ISO1600
=> about 2 stops advantage to the 1000D
(you may disagree here - but let's just run with that for the sake of
argument)

That is not the only difference. You can have long exposures on a DSLR, lasting into the minutes, but you are limited to no more than a few seconds at the most on a compact digital camera.

This means that I would get around 0.5 stops advantage going with the
1000D with its kit lens, which is not much.

However, I have seen a couple of posts where users say that the
apertures of P&S cameras and DSLR cameras aren't comparable because
of the different sensor sizes, and claiming that f/4.0 on a DLSR is
actually no slower than f/2.8 on a P&S.

Aperture is a universal measurement. It is determined by dividing the diameter of the front element by the focal length. So, if you have a 50mm lens and the front element is 25mm in diameter, then you have a lens with a maximum aperture of 25/50 or 1/2 or f/2. Nevertheless, the stated "ISO" of the compact digital cameras may be inaccurate. For years, Canon's DSLR cameras have ISO settings that are more sensitive than is marked, by about 1/3 of an f stop. So, the statement above may be reflective of the overstated ISO values on compact digitals and the somewhat understated ISO values on some DSLR cameras.

Regardless, you should consider a DSLR as your best option for best low light performance. Unless and until compact digitals have larger sensors and larger pixels, they will not perform well in low light situations.

 

[GaryW]

Anastigmat wrote:
...

That is not the only difference. You can have long exposures on a
DSLR, lasting into the minutes, but you are limited to no more than a
few seconds at the most on a compact digital camera.

My old 3mp Nikon had a BULB mode, although I can't recall if that required the optional electronic remote trigger. My current Sony P&S goes to 30", which isn't bad.

But, yeah, there are a lot of little features which make a DSLR more desirable at times that may not seem essential at first.

...

Aperture is a universal measurement. It is determined by dividing

It is universal, but when you consider a similar FOV between two different kinds of cameras, the size of the aperture opening is then different. I suppose what David & I are curious about is how to gauge the difference performance even if at first the f-number appears to be the name.

the diameter of the front element by the focal length. So, if you
have a 50mm lens and the front element is 25mm in diameter, then you
have a lens with a maximum aperture of 25/50 or 1/2 or f/2.
Nevertheless, the stated "ISO" of the compact digital cameras may be
inaccurate. For years, Canon's DSLR cameras have ISO settings that
are more sensitive than is marked, by about 1/3 of an f stop. So,
the statement above may be reflective of the overstated ISO values on
compact digitals and the somewhat understated ISO values on some DSLR
cameras.

I'm now sure this is what I'm seeing.

Regardless, you should consider a DSLR as your best option for best
low light performance. Unless and until compact digitals have larger
sensors and larger pixels, they will not perform well in low light
situations.

Even with the DSLR, I can still run into situations where things seem too dark and imperfect... then I remind myself that I'd be worse off with a P&S and go on. I took my P&S with me to an event recently and had to use high ISO; the results were marginal, but maybe good enough for 4x6's....

--
Gary W.

 

[GaryW]

Aperture is simply a ratio of the focal length vs the "effective"
diameter of the lens.

In P&S cameras the focal length is a lot smaller than SLRs so is the
width of the lens though, effectively giving the same f stop.

So let's say that at 7mm, my P&S gives the same FOV as 24mm on an APS-C DSLR, and I'm trying to decide which camera to use. With both set to f2.8, the actual aperture sizes are 2.5mm and 8.5mm.

Does that help me to decide which camera to use? Maybe in bright light it doesn't matter, but at some point it does....

think of it as, big / big = small / small

Sounds like small

If im still not clear:
http://en.wikipedia.org/wiki/F-number

--
Gary W.

 

[GaryW]

David B Burnette wrote:
...

Yes, Gary, it was you responsible for my confusion!

Thanks! ;-)

Seriously though, I thought it was worth starting a thread on this
issue, as I really wanted to know if the exposures on P&S and DSLR
cameras could be directly compared to see how much many stops
advantage you got when going to DSLR for low light photography.

....

No, I think it's a great topic. Many people are trying to make the choice...

--
Gary W.

 

[Manehead]

f2.8 on a P&S and f2.8 on a DSLR are only the same in that the amount of light that hits the sensor per unit area is the same.

The difference is the fact that on a P&S, you have a lot more photo cells per unit area, therefore each cell will get less light.

Hence more gain needs to be applied to each cell on a P&S to obtain the same exposure as on a DSLR. This results in more noise.

What this means is, comparing the minimum f-numbers on a P&S with a DSLR is irrelevant for low light photography. What really matters is the amount of light per photo cell . This is the value you should be comparing between P&S and DSLRs, and you should find that DSLRs do much better than any P&S on this front.

 

[David B Burnette]

Ok, that settles it! I've ordered my EOS 1000D with 18-55mm kit lens. Serves me right for trying to convince DSLR users that I should by another P&S...

I actually owned an SLR film camera around 5 years ago before I went digital, so I don't imagine digital SLR will be that much different. Then DSLR was very expensive so I settled for a P&S when I went digital, but I to remember missing things like the creative control you had with DOF. Film photography was just such a damn expensive hobby, though.

Anyway, thanks for everyone's feedback and I look forward to reporting back on how I get on.