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

Started Jan 26, 2014 | Discussions thread
Re: A reminder for some members as to what the F stop is all about.
5

They say things like " convince me, that the amount of light going through Olympus 25/2.8 is the same compared to Canon, e.g., 50/1.4 set to 2.8". I have to disappoint you.

Let save this statement, because the facts are about to get twisted very soon. Notice that in this comparison, the focal length of the Canon has doubled, as it should (but later . . .)

also there is a lot of "expert talk" that bigger lenses allow more light and therefore this results in less noise in the image. This is total BS.

How can any sane person NOT think a bigger lens lets in less light? So, astronomers have no interest in bigger telescopes? Really, this discussion should stop right here with this statement.

Now let's go through some lesson of optics. Some people visiting this website have no knowledge about the school items like : candela (don't confuse with Nelson Mandela), lumen, brightness, decibel, voltage, Amper, semiconductor electronic noise level, relative to signal vs absolute, etc.

And some are optical experts, rocket scientists, electrical engineers, with years of training in doing this stuff. Which one are you?

So, F2 on a lens means that this diameter of the opening of the optical instrument can fit TWO times into its focal length. For a 50 mm F2 lens it means that the aperture diameter at F2 is 25 mm.

Ah, but now you've conveniently forgotten that the Canon needs twice the FL for the same FOV, as you correctly pointed out before. By your own (correct) math, the M43rd 25MM lens has an opening of 12.5MM and the equivalent 50MM Canon lens has an opening of 25MM. Oops, twice the diameter, four times the light. This isn't rocket science. For the same FOV, you have half the FL in M4rds, which is half the diameter and four times less light.

Simple. No degree necessary.

Now about the sensor noise on FF cameras vs. 4/3 vs anything else. The ONLY reason why they (FF) have less noise and better dynamic range is because their individual photosites are BIGGER electronic devices. Any semiconductor/ transistor/ diode has its electronic noise, because inside its P-N-P or N-P-N layers there are electrons which move randomly even when there is no "useful" signal. This chaotic movement is called "noise". A bigger semiconductor device can put through higher DC current and have "relatively" less noise.

It's funny when non-technical people try to (mis)describe well known analysis. The bulk of the noise is due to the quantum nature of light, and it's inherent randomness. Less light = more randomness = more noise. Actually, the number of errors in this one paragraph is staggering. Sensors aren't diodes, sensor don't carry current, and sensors have noise due to thermal contributions.

This is kind of like flat earth arguments, where a non-technical person hijacks a lot of technical information he doesn't understand, and twists it to his point of view.

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