A reminder for some memebers as to what the F stop is all about.

Started Jan 26, 2014 | Discussions thread
Great Bustard Forum Pro • Posts: 43,009
And the answer is:

DonSC wrote:

Great Bustard wrote:

Wow. Just wow. Everything you wrote is entirely incorrect, and I will prove it wrong with a single example that you can all do at home.

Let's take a photo of a scene with an E5 + 35-100 / 2 at 50mm f/2 1/200 ISO 3200 and 100mm f/2 1/200 ISO 3200 (note that we have used the same lens, same f-ratio, same shutter speed, same ISO, same sensor, and thus same sensor efficiency and pixel size).

We now crop the 50mm photo to the same framing as the 100mm photo and display both photos at the same size. Which photo is more noisy and why?

(Hint: while the sensors are the same size, the cropped photo uses only 1/4 the area of the sensor, and thus only 1/4 as much light makes up the cropped photo as the uncropped photo.)

We have a 300mm f/2.8 on a Canon 1Dx and a 300mm f/2.8 on a Olympus E-M1. Same ISO. Both cameras are 16 MP. Now crop the shot from the 1Dx to fit the FOV of the E-M1. What image has less noise? What image has less detail?

Instead of "same ISO", how about we say, "same f-ratio and shutter speed", as the ISO setting isn't particularly relevant to the matter at hand, and the cameras may not meter the scene the same at the same ISO setting.

Then the EM1 photo will have less noise since it has a more efficient sensor. The EM1 photo will be more detailed since it has 4x as many pixels on the subject.

Now let's assume we had a FF sensor made with the exact same pixels as the EM1 sensor.  Then the photos would be all but identical.

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