Originally posted by jyndi That... does not make sense. What are you meaning here by exposure?
Same f-stop and shutter speed at the same FOV. Why this happens is because even though it's the same exposure, the physical aperture (the lens iris opening) is larger on the FF combo.
For example:
50mm f/2.8 (FF) == 50 / 2.8 == 17.85mm physical aperture
35mm f/2.8 (aps-c) == 35 / 2.8 == 12.5mm physical aperture
This link talks about it more if you want a good intro:
a good read on the subject from dpreview Quote: 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.
Yes, you would be correct - the light
density (or intensity if you prefer) at the same f-stop is the same (light volume pr sq/mm,) but the total light being used to create the image is more because of the larger physical aperture needed for that FOV. More light being used to create the image results in less noise in the overall image.
Quote: 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.)
The greater amount of total light being collected by the larger sensor area is what causes the image to surpass the smaller sensor - if you re-sample more MP down to a normalized image, you can't create light - in other words, if re-sampling worked that way you would be able to create an apsc- sensor with 100MP, and the re-sampling down to 16MP would beat every native 16MP aps-c sensor out there, simply by re-sampling.
What you can and should expect is for sensors
of the same size and similar gen, re-sampling the higher-res one down to the lower-resolution
matches the lower res one, even if the per-pixel performance of the higher-res one is worse - and we have multiple examples of that, like the K3 vs. K5. When one sensor is larger, and the images were taken at the same exposure and FOV, the larger sensor when re-sampled will beat the smaller sensor in SNR of the resulting image - almost irregardless of pixel density. Meaning, you will not find a 12, 18, 24, 36 or 43MP FF sensor that is 'beat' by an aps-c sensor of similar gen, of any MP - because more light went into those FF images in the first place.
Quote: 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.
In order to get the same FOV and exposure at the same time, DOF does need to vary, yes - an important aspect of equivalence that you need to be aware of.
You have to be willing to 'accept' 1.3 stops less DOF to 'get' the better noise perf from the larger sensor. (I say 'accept', but in many cases it's not a negative to have less DOF, and in many cases it doesn't make any real difference to the shot - think shots where the whole subject is easily in the DOF in either case, or youre near hyperfocal.)
Quote: (Please tell me if that was coherent!)
Absolutely.
Quote: 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.
No, this is a common misconception. In a same-gen comparison, a larger sensor with greater pixel density than the smaller will still show less noise. It's about sensor area there, along with the mandated larger physical aperture at the same exposure for that FOV. Really, really, it is
I can provide some external references if you wish for further reading - what I've found is it's very instructive to 'listen in' on a conversation where one of the conferees happens to be Eric Fossum, or Bob Newman, or Joseph Wizniewski - you know, the people who designed the hardware and software we use to create our delicious images
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---------- Post added 03-17-16 at 12:56 PM ----------
Originally posted by bxf The same arguments are presented over and over and over. The one thing that I am repeatedly failing to understand is Clackers' insistence that DXO's SCREEN tab is the relevant one. Sure, I understand his argument with respect to pixel/RAW noise, but in the end, one has to perform comparisons on the end result, i.e. a print or screen image. In either medium, the images from the different sensors must be produced to the same given size in order for the comparison to be meaningful. As I understand it, such a comparison is represented by the PRINT tab on the DXO graph.
Why is this even arguable?
I don't know. I just hope he can dial it and try to remain civil so this thread can continue to be useful. (But he's demonstrably wrong, stay tuned.)