

Started Feb 8, 2014 | Discussions thread
Great Bustard Forum Pro • Posts: 38,406
Re: Necessarily.

Heyseuss Hoolio wrote:

Great Bustard wrote:

For whatever reason, people are hung up on the intensity of the light, and fail to understand that it is the total amount of light that matters, and this can be demonstrated with perfect clarity with the following simple experiment y'all can do at home:

Take a photo of a scene from the same position at, say, 15mm f/2.8 1/100 ISO 3200 and 30mm f/2.8 1/100 ISO 3200 with the same camera. Crop the 15mm photo to the same framing as the 30mm photo and display both at the same size. Which is more noisy and why? After all, it's the same sensor (thus same efficiency and pixel size), the same intensity of light on the sensor, the same shutter speed, and the same ISO.

SPOILER ALERT (answer follows): the 15mm photo cropped to the framing of the 30mm photo is more noisy because it was made from 25% the light as the 30mm photo.

Now you're talking about up-sizing a cropped photo...

You can downsize the larger 30mm photo, if you choose.

...of course it'll have degraded image quality compared to a native image.

For two reasons: less light made up the crop (making it more noisy) and fewer pixels make up the crop (making it less detailed).

I'm really trying to understand the example. How about re-wording it. Same camera, you take a 15mm f2.8 image and then move back and frame the same image at 30mm f/2.8, both same resolution and same information hitting the sensor.

In this case, the same total amount of light falls on both sensors.  The 15mm photo was twice as close, so four times as much light reaches the aperture (inverse square law).  The aperture diameter of the 30mm photo has four times the area, so four times as much light reaching the aperture passes through the lens onto the sensor.  Thus the same total amount of light falls on the sensor in each case.

Again, it is all about the total amount of light falling on the sensor.

I think really what we're looking at is pixel density as you said, which I didn't think about before, which is causing less noise overall. Both sensor sizes a whole are getting f2.8 light intensity but the FF image is still capturing more light information per pixel, thus lower noise. Even the 36MP FF sensor still has larger pixels than a 16MP m4/3 sensor.

Again, the noise is *entirely* a function of the total amount of light that makes up the photo and the efficiency of the sensor.

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