Crop Factor, Low Light and Aperture with m4/3 lenses?

Started Jun 15, 2014 | Discussions thread
Anders W Forum Pro • Posts: 21,468
Re: Very simple:

Just another Canon shooter wrote:

Anders W wrote:

Just another Canon shooter wrote:

Anders W wrote:

FF has the same noise for equivalent images only if the sensors are equally efficient. But as a rule they are not. Smaller sensors tend to be more efficient than larger. See here:

Not true. QE of newer sensors is about 53%, see sensorgen, from m43 to APS-C to FF.

Sensorgen doesn't have data for many of the sensors in my sample and are based on fitting curves to numbers that results from previous curve fitting.

It does, for the most relevant bodies.

Why should we use partial data if we can use more complete data? And why should we use fitted data points if we can use real data points?

Further, QE is an indirect measure

It is what it is, it has a clear definition.

That does not help. My measures are just as clearly defined but closer to what we are interested in: Image quality.

that doesn't take certain facts into account (e.g., fixed pattern noise and read noise).

It should not. Read noise is a different parameter.

It is different from QE, yes. So what? What we are interested in is the signal-noise performance. Read noise is part of that.

My more direct measures are not subject to any of these problems.

I did not read your posts and I do not have to.

If you want to argue convincingly, I am afraid you have to.

You are trying to give your own definitions,

I use DxO measures.

then to compute the "efficiency",


and then what - to compute the noise?

No. What makes you think that?

But DXO measured the noise. What is the point of your exercise then?

I make no attempt to measure noise as a stand-alone quantity. Like DxO, I measure what we are interested in from an image-quality point of view: Signal-noise performance.

DXO measured 2 stop difference at 18% gray. This is the theoretical factor, so we have the same QE.

See above regarding QE.

This is based on the theoretical model here, and also somewhere on the DXO site. So, same QE, as simple as that. We do not really know what it is, but we know they are the same.

The efficiency with regard to signal-noise performance, which is what we are interested in for the purpose of comparing image quality is not the same.

About DR - DXO measured that as well. Difference about 1.2 stops or so, short of 2 stops.

Yes, less than two stops on average and sometimes even negative. Since DR is a good measure of signal-noise performance in dark tones/areas and since that is more perceptually important than signal-noise performance in brighter tones/areas, the difference in image quality between FF and MFT at the same ISO is significantly less than two stops.

Since they define ISO as the saturation level, that tells you what the read noise is.

Yes, you can compute the read noise if you want. So what? What I study is signal-noise performance.

Pattern noise is not a problem with newer FF bodies at high ISO

So what?

- only with Canons at low ISO but m43 cannot even capture so much light, so what is the point of discussing it.

Because it affects the signal-noise performance in which we are interested.

But for that, you need, say, f/1.4 vs. f/2.8, and the sensor would not be able to register at least 1/2 stop of that light, you get a noticeably lower resolution, etc.

I would need f/1.4 vs f/2.8 only if the sensors were equally efficient. My point is that they are not.

Of course, by "for that", I meant to realize the hypothetical "efficiency advantage". Then you must be at equivalent apertures.

No. The efficiency advantage of smaller sensors means that they can go equal with larger sensors at less than equivalent apertures.

What FF can do is to take non-equivalent images, as simple as that.

Yes. Nobody disputes that. What I disputed was your claim that it can take equivalent images just as well as smaller sensors as far as noise is concerned.

Noise and resolution are related, so higher resolution helps offset some part of the noise.

The comparisons I perform are with resolution held constant (DxO "print mode") so any differences in sensor pixel count are already properly accounted for.

Since smaller sensors tend to be more efficient than larger, that's not the case.

Since they are not, it is not.

I have undertaken a systematic analysis showing that smaller sensors tend to be more efficient than larger, no matter whether we consider lower or higher ISOs and no matter whether we consider the brightest or the darkest tones. You haven't shown anything.

Just asserting things doesn't help. Where's your data? Where's your statistical analysis? Come back when you have something to report. Then we can talk again.

Yes. DR is part of the efficiency of the sensor.

It is not. You want to make it though.

You are confusing quantum efficiency with sensor efficiency more generally. QE is one measure of sensor efficiency. It is inferior to those I use in being a less comprehensive and less direct measure of signal-noise performance, which is what we are actually interested for the purpose of comparing image quality.

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