comparing lens + sensor size combos for low light

[blue_skies]

So I will start the question with an example. Given these two combinations with premium type lenses:

a6000 type camera (APS-C sensor) + 1670z @ F4

vs

Om-D EM EM5 type camera (m43 sensor) + 12-40 F2.8

The m43 sensor is half the size of the APS-C sensor, and typically the larger sensors are better for reduced noise in shadows and low light conditions for the same generation.

However, the m43 lens is a much faster lens in respect to the size of the sensor. Furthermore, the small sensor means that the DOF for the m43 sensor will be larger, thus one can employ a smaller aperture and not worry about parts of the image being out of focus in situations where there is no specific focal point.

I am not so much asking which lens/system is better; as they are both making different compromises it terms of sharpness/weight/size/DOF capabilities, etc. Both are awesome cameras.

Rather, I am more interested in how does one compare across formats. Presumably, the reason why the 1670z is F4 and the 12-40 is F2.8 is that designing a F2.8 for an APS-C sensor would result in a larger lens. Thus there is a trade off here. Do we go for a smaller sensor and smaller aperture number or a larger sensor with a higher aperture - what is better for low light when you bring the issue of lens size in the equation?

Well, the true answer is neither. By picking the zoom lenses, you have somewhat leveled the playing field, but f/2.8 on m43 at 16mp compares to f/5.6 at FF, and f/4.0 on APS-C at 24Mp compares to f/6.0 at FF. Downsampling from 24Mp to 16Mp will help the APS-C a bit, so I would gather than the two zooms are at a similar performance level.

Change to two prime lenses, e.g. f/1.8 on both (with similar FOV), then the APS-C will pull almost a stop ahead. This is noticeable in lower ISO, less noise, higher DR, easier to pull up shadow noise, and so on.

I you limit yourself to the zoom lenses (either system), I would also limit myself to daytime usage only. Both system will then perform similarly.

But for indoors, and low light, I would switch to a fast prime lens and I would chose the camera with the largest sensor and trade less DOF for less noise. It also makes for more impressive and more pleasing images.

The A6000 will be a clear winner then. Especially if you consider a RAW workflow.

--
Cheers,
Henry

 

[lumigraphics]

The equivalent aperture tells you what aperture on a full frame lens would give the same depth-of-field and the same total light as the one you're assessing.

The whole "total light" business is WRONG WRONG WRONG.

Remember that image size changes, so that your "4 times" is spread across a larger area to create the same image on the sensor.

There are other reasons that a larger sensor gives better IQ, but the total amount of light hitting it is NOT the reason.

 

[AHM]

The equivalent aperture tells you what aperture on a full frame lens would give the same depth-of-field and the same total light as the one you're assessing.

The whole "total light" business is WRONG WRONG WRONG.

Remember that image size changes, so that your "4 times" is spread across a larger area to create the same image on the sensor.

There are other reasons that a larger sensor gives better IQ, but the total amount of light hitting it is NOT the reason.

 

[Dennis]

Total light is MEANINGLESS. It has no importance to anything and is a derived value. I have no clue why people talk about it as if it is important.

The only thing it does is to show who is clueless.

--
David M. Converse
Lumigraphics
http://www.lumigraphics.com

And your authoritative source is...?

C'mon, give him a break ... he DID put "meaningless" in all caps, so it must be true.

(Though I have to say, whether he knows why big sensors do better or not, his gallery kicks my gallery's a** !)

• Dennis
  --
  Gallery at http://kingofthebeasts.smugmug.com

 

[Jerry R]

David,

Your not going to get any where with the Total Light religious fanatics.

 

[Pixel Pooper]

Total light is MEANINGLESS. It has no importance to anything and is a derived value. I have no clue why people talk about it as if it is important.

The concept is useful for answering questions such as the one asked by the OP.

The only thing it does is to show who is clueless.

It does that too, somewhat ironically in this case.

 

[Dennis]

David,

Your not going to get any where with the Total Light religious fanatics.

Hmmmm ...

AHM posts that dpreview's article is the source of the information on total light.
David says "You're WRONG WRONG WRONG"
AHM asks for a credible source.
David says "total light is MEANINGLESS"

And somehow AHM is the "religious fanatic" ?

Pretty funny, Jerry. In any event, you're right about him "not going to get anywhere" if the best he can do is shout "you're wrong and I'm right".

• Dennis
  --
  Gallery at http://kingofthebeasts.smugmug.com

 

[FingerPainter]

Total light is MEANINGLESS. It has no importance to anything and is a derived value. I have no clue why people talk about it as if it is important.

The only thing it does is to show who is clueless.

 

[Pixel Pooper]

David,

Your not going to get any where with the Total Light religious fanatics.

Does "religious fanatics" best describe those who use mathematics and testing to reinforce their claims, or those who type in capitals to refute things they don't understand?

 

[FingerPainter]

Suggested reading:

http://www.dpreview.com/articles/2666934640/what-is-equivalence-and-why-should-i-care

Yes, the link came up previously in the discussion, it is a good explanation.

If we take a night shot and keep the DOFs different, then the larger sensors will produce less noise. If the DOFs are kept the same, then the sensors display approximately the same noise, as shown in the demonstration they did since the larger sensors will have to use a higher ISO:

http://www.dpreview.com/articles/2666934640/what-is-equivalence-and-why-should-i-care/4

Well, almost. They'll have about the same noise because the larger sensor will be using a lower exposure to get the same DOF. The lower exposure is what increases the noise. Raising ISO doesn't inccrease noise. It might actually reduce read noise. We associate higher ISO's with more noise because we tend to raise ISO when the exposure is low It is the low exposure which actually causes the increase in noise.

 

[jackalopemaui]

The equivalent aperture tells you what aperture on a full frame lens would give the same depth-of-field and the same total light as the one you're assessing.

The whole "total light" business is WRONG WRONG WRONG.

Remember that image size changes, so that your "4 times" is spread across a larger area to create the same image on the sensor.

There are other reasons that a larger sensor gives better IQ, but the total amount of light hitting it is NOT the reason.

--
David M. Converse
Lumigraphics
http://www.lumigraphics.com

Sorry David, but I believe you are wrong about AHM being "WRONG WRONG WRONG" about total light. An aperture of f/2 on uFT is equivalent to f/4 on FF. The f/4 will produce 1/4 the light intensity of f/2, but on a FF sensor it will be spread over 4 times the surface area, so 4 x 1/4 will give it the same total light as F/2 on uFT

Yes, I didn't write the above, DPReview did. David, if you think that is wrong, provide an AUTHORITATIVE reference. The people on DPReview are not fools. And it is common sense. The iPhone has an F/2 lens, so that would make it better than most FF lenses in low light. Of course not. And don't give me some airy, vague discussion about sensor quality. Numbers, please. Equivalent aperture provides this, and this is the best way of comparing different sensor sizes at low light (and DoF).

People rejecting equivalent aperture reminds me of people denying global warming or evolution.

Total light is MEANINGLESS. It has no importance to anything and is a derived value. I have no clue why people talk about it as if it is important.

The only thing it does is to show who is clueless.

--
David M. Converse
Lumigraphics
http://www.lumigraphics.com

If you don't understand, BE QUIET. Total light does matter because it affects image quality. Total light difference is the REASON why a larger sensor is better than a smaller sensor

 

[Jerry R]

Dennis,

I had a long discussion with someone on a recent thread about this and understand why the total light concept seems "right". When you down size images for "print" comparisons as DXomark does you are combining pixels of the larger sensor to compare with smaller sensors. There is an excellent video (I don't recall the link) comparing the A7R with the A7S.

When the A7R was downsized to 12 megs it compared well with the S/N of the A7S and maintained the better resolution. The A7R S/N compared well well with the A7S because of the combining of pixels when downsized to 12 megs.

S/N due to photon statistics is a result of the individual pixels light gathering ability. This is why a 24 meg FF sensor has better S/N than a 24 meg APSC sensor, the pixels are lager on the FF sensor and collect more light than the smaller pixels on the APSC sensor.

I understand why people say larger sensors gather more light than smaller sensors., it is because of the larger pixel light gathering area on the larger sensors.

 

[Jerry R]

Pixel peeper my reply to Dennis,

I had a long discussion with someone on a recent thread about this and understand why the total light concept seems "right". When you down size images for "print" comparisons as DXomark does you are combining pixels of the larger sensor to compare with smaller sensors. There is an excellent video (I don't recall the link) comparing the A7R with the A7S.

When the A7R was downsized to 12 megs it compared well with the S/N of the A7S and maintained the better resolution. The A7R S/N compared well well with the A7S because of the combining of pixels when downsized to 12 megs.

S/N due to photon statistics is a result of the individual pixels light gathering ability. This is why a 24 meg FF sensor has better S/N than a 24 meg APSC sensor, the pixels are lager on the FF sensor and collect more light than the smaller pixels on the APSC sensor.

I understand why people say larger sensors gather more light than smaller sensors., it is because of the larger pixel light gathering area on the larger sensors.

 

[Dennis]

Dennis,

I had a long discussion with someone on a recent thread about this and understand why the total light concept seems "right".

There's a lot to learn on these forums ... I was firmly in the "f/2.8 is f/2.8" mindset before someone patiently went through equivalence with me. I think one think people object to is a notion that just because it gets brought up in technical comparisons, somehow people are saying it's something you need to be concerned with. And it isn't ... it's nice to know and handy once in a great while, if you ever have the need to comparison shop across sensor sizes ... but is otherwise something you don't need to think about. I'd hazard to guess that most of the worlds best/talented/successful photographers rarely or never think about total light or equivalence (The concept that some aspects of IQ depend on putting as much light as possible on the sensor without blowing highlights is helpful, but a lot of people get there from reading about ETTR anyway).

• Dennis
  --
  Gallery at http://kingofthebeasts.smugmug.com

 

[Jerry R]

Dennis,

I had the opportunity to spend several hours with a professional landscape photographer many years ago BDP (before digital photography).

I don't think he ever hard of quantum chemistry and how film emulsions really worked. But, he understood the effects of light reflecting off of different surfaces, the effect of morning and afternoon light, and many other factors of light behavior and how it effects a picture.

Gave me a lot to think about. So does size really matter? Depends on context.

 

[Jerry R]

Camera sensors have only one ISO, base ISO. Increasing "ISO" just amplifies the signal seen by the sensor. Simple way to prove this is to take an exposure at 6400 ISO and then take the same picture using the same f/stop and shutter speed at base ISO (100 for many cameras). Increase exposure in PP and you will have about the same image taken at 6400 ISO.

 

[Dennis]

I don't think he ever hard of quantum chemistry and how film emulsions really worked. But, he understood the effects of light reflecting off of different surfaces, the effect of morning and afternoon light, and many other factors of light behavior and how it effects a picture.

Just an aside: without doing any math, without thinking about any of this equivalence stuff, I bet he also probably had a good idea of what 35mm versus medium format versus sheet film could do. Anyway ...

The funny thing is that this (sensor size, mtf charts, etc) is all the stuff that's easy to bandy about when killing time online. And what you mentioned is the stuff that's important when we actually have a camera in hand. It would be great if there was a productive and enjoyable way to talk about that as well, but I don't really see it happening. It seems more like what you'd do with a mentor (like you did) or a small group of friends ... how do you have meaningful ongoing discussions about what's important in photography with thousands of strangers in a forum ? You run into the same old problem that everything's already been said before, but at least with gear, there's always something new (or rumored) to argue about.

I read a few articles/remembrances about Mary Ellen Mark recently. One was a summary of lessons that someone learned from her and these are the author's words, not hers - one of the lessons was that good photography isn't about the f-stop, it's about being able to talk to people. For some kinds of photography, that may not be true, but whether it's talking to a subject or talking your way into opportunities, I bet it's very true of many successful photographers who would shake their heads at what we "waste our time" talking about here. But it's a fun waste of time

• Dennis
  --
  Gallery at http://kingofthebeasts.smugmug.com

 

[Jerry R]

Dennis,

I'm sure he new the difference between medium format and 35mm, that's why he used an 8x10 view camera.

Jerry

 

[DrLogic]

Forget the IQ difffernces. Both camera's and lenses are great and will deliver stunning pictures. What is way more important is the feel of the camera. Go to a shop and rty them out. feel them, handle them, when possible take pictures with them (not to compair, but to feel how the cameras work. Try to change settings, look at the menu etc. gofor the camera you find handling best.

Yes. I thought both cameras were very good, and in fact I did so say explicitly because I didn't want this thread to turn into another of those "my camera is system is better debates", but rather wanted to see how I would expect them to operate in the evening in low light - and I was curious if smaller sensor with smaller aperture number compared against larger sensor and bigger aperture number, since they seemed to be roughly the same weight/size.

I do agree with you that in buying cameras, trying them out is a good way to compare (well I already have the a6000 so I don't need to try that one in a shop).

I know this is a gear forum and people are talking about gear, but the IQ of these cameras and lenses is that high that in normal world pictures (printed o seen on your big screen TV) are very close so no need to think about that.

Agreed.

Others here have told what (in theory) is the best combination, but when you go primes things will be a bit different again. Most primes on both systems are arround f/1.8 so when using those primes the A6000 might be the best camera (again mainly when pixel peeking so in real life pictures not that much of a difference...) What is maybe of a big importance for you is the following;

What system has the lenses you want or need?
What system will you take with you the most (is one system (much) larger then the other, take lenses in this too)
What system do you like best (do you like the A6000 formfactor or the formfactor of the m43 camera of your choice)
What is the price of a complete system?

You make valid points, I agree with your points.

 

[Pixel Pooper]

Pixel peeper my reply to Dennis,

S/N due to photon statistics is a result of the individual pixels light gathering ability. This is why a 24 meg FF sensor has better S/N than a 24 meg APSC sensor, the pixels are lager on the FF sensor and collect more light than the smaller pixels on the APSC sensor.

This is not true. It is the sensor size that matters, which is why if you compare APS-C and FF sensors the FF performs better regardless of pixel size. DPR did an article on it recently.