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Forum: Pentax Full Frame
03-16-2016, 06:53 PM
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That... does not make sense. What are you meaning here by exposure? In this context, I take it as the light volume registered per square mm of sensor - it's independent of total sensor area. But assuming the same light volume per square mm and the same iso setting, then the noise level per pixel will be the same. Each square mm of sensor doesn't know if it's part of a large sensor or a little sensor - it generates the same sensor noise regardless. (Although, if they're cut from the same wafer, the larger sensor has -more pixels-. So if you downsize the result to the same dimensions as the smaller sensor, sure, the larger sensor has less noise. You're losing noise with the downsampling (along with resolution). But if you're not downsizing, then the noise in each 100% crop is inherently the same, because it comes from the sensor.)
But... that doesn't mean you can get an identical image out of them, though, because in order to get the same FoV and ISO, aperture and consequently DoF must vary. If you want to hold the DoF and FoV constant, then ISO must vary (due to, as you say, different light volume) and on the 'cut from the same wafer' pair of sensors, that means they will have a different level of noise. But that is a result of a choice to vary ISO in order to duplicate FoV -and- DoF across the two sensors, it isn't that a smaller sensor cut from the same wafer suddenly has different noise characteristics by being cut smaller.
(Please tell me if that was coherent!)
Which comes down to... if you are trying to capture an image strictly defined by it's FoV and DoF, then the smaller sensor will need a higher iso setting. Higher iso = higher noise, if the sensors are 'same wafer' identical tech. Hence, larger has less noise. How much difference than makes in the the real world is mostly 'not much' and occasionally 'a lot'. Which side of that fence an individual's photography falls is made up of way more factors than the nice little exposure triangle has.
This one is a case where the sensors are not from the same wafer. They both have the same 16 megapixels, but with the D7000 being larger, the pixels are larger. The difference isn't from the size of the sensor, but in the size of the pixels on the sensor.
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Forum: Pentax Full Frame
03-15-2016, 07:55 PM
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... but isn't inherent noise determined mostly by two factors - the age of the sensor and pixel pitch? With processing by the camera to generate the RAW file being the first noise-filter?
That aside:
I do not have a Canon 5DIII or 5DS, but I had a D7000 and I have an oly EPM2, one of the bottom tier m43 cameras that has the 'same' sensor as the top tier Oly m43 cameras. Quite frankly, I've had shots wrecked by noise from both cameras - the problem was always the idiot holding the camera(me), not the camera itself. I had also managed to take some shots with both that I really really like and which are not discernibly noisy when viewed in smallish prints or on screen. I've even got a couple from each which I have printed medium-ish without noise being noticed as an issue. That's the practical point that it really isn't an issue compared to the skill (or lack of it) of the photographer. However, without a doubt, the best shots in terms of noise levels were with my D7000. The two cameras are both nominally 16MP and I think the sensor tech is reasonably close. So the lower pixel density on the D7000 probably made the difference when the other factors (lighting, subject, etc) aligned to support it's somewhat better capabilities.
So yeah, all things being equal, a smaller sensor does give more noise. That is a reasonable expectation from a technical point of view. Why is that something to argue about?
(Well, aside from that common impulse to argue that our personal choices are the best choices period instead of just best for us. I mean, I decided the extra IQ I could sometimes extract from the D7000 to be insufficiently worthwhile to keep it when m43 came so close and was so. much. smaller. That's the compact vs. DSLR argument really. I do plan to get a K1 as I think that's enough of a performance leap to be worthwhile... for me.)
I do think too that the oly m43 cameras demonstrate just how much the processing tech can affect noise too. The OMD cameras - EM1/EM5/EM10 technically have the same sensor as my little EPM2. But they do produce cleaner images - because Olympus has refined their ability to extract data from that sensor read-out.
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