f-number equivalent between m43 and FF

Started Mar 25, 2014 | Discussions thread
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Re: f-number equivalent between m43 and FF

dwalby wrote:

Allan Olesen wrote:

D Cox wrote:

The total area of the sensor is irrelevant. If you put the same lens on various sizes of sensor, the noise level in the part of the image that they all record will be identical. (Assuming they are the same generation of technology.)

Let us compare the Nikon D800 (FF, 36MP) and the Nikon D7000 (APS-C, 16MP).

Same pixel size. Same Sony sensor technology. Same noise per pixel if you expose equally (same f-stop, shutter speed and scene light).

But not same magnification of the final output.

If you take the same photo with these two cameras and enlarge to the same output size, each pixel from the D7000 will be magnified 1.5x more in each direction. Consequently, the final output will appear more noisy.

And you can't really say I am wrong about that because I am actually just repeating your own claims from another post in this thread: The same pixel will look more noisy the more you magnify it.

So yes, it is all about sensor area.

I agree its all about sensor area...

It's not all about sensor area -- it's all about the total amount of light falling on the sensor and the efficiency of the sensor.

...but I'm not sure I agree with your example.

In the case of two sensors of different size, but with the same size pixel, you have the same SNR for each pixel, we all agree on that.

What does per-pixel SNR have to do with the noise in the photo?

Where I don't necessarily agree with you is that the simple act of printing the pixel larger or smaller will have any effect on its SNR. Back to the blue sky example, if you have high per pixel SNR a field of blue pixels will have a more uniform set of values than something with a lower per pixel SNR, and appear less noisy, because it is. But in the case you describe, where the per pixel SNRs are equal, the difference in adjacent pixel values due to the noise will be the same, the only difference is how far apart those differences are spaced on the print. So I think in your example the 36MP image will have the same noise as the 16MP image regardless of how large each is printed. The main difference will be in the resolution of the 36M image being able to print finer detail than the 16MP image. The pixels themselves don't get any noisier simply by being enlarged to print over a larger print area.

Take a picture of the sky at, for example, 50mm f/5.6 1/400 ISO 100 and 100mm f/5.6 1/400 ISO 100.  Crop the 50mm photo to the same framing as the 100mm photo.  Display both at the same size.  Which photo is more noisy?

What I'm not sure about though, is if seeing the pixel-to-pixel noise variation spaced closer together in the 36MP print, as opposed to further apart in the 16MP print, produces a result that appears to have less noise to the eye when viewing the prints. I've never experimented with that to have an opinion, so if that's the case I won't try to argue that, but I would still claim that the per pixel SNR continues to be the same regardless of magnification. The value of the pixel remains the same regardless of how large you print that pixel, so I'd argue because of that its impossible to make it more noisy simply by printing it bigger.

Which do you think is more noisy?  The photo below:

or a 100% crop of it displayed at the same dimensions?

In the case of two sensors of different size, with the same number of MP, then the larger sensor will have more area/pixel, more photons/pixel, and therefore higher SNR per pixel. I think we probably agree on that, in which case both prints at the same size will favor the larger sensor due to the higher SNR of its pixels.

The larger sensor will have less noise than the smaller sensor regardless of pixel count for a given exposure and sensor efficiency.

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