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

Started Jan 26, 2014 | Discussions thread
bobn2 Forum Pro • Posts: 62,183
Re: A reminder for some memebers as to what the F stop is all about.

gsergei wrote:

Hi, all.

I've just had a quick look at the thread started by Dave Gaines about equivalence , again. He has made a very good point overall. Surprisingly, there are still photographers who fundamentally don't know what the aperture is all about.

If you're going to make statements like that, best to ensure that you know 'what aperture is all about' in the first place.

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: YES ,it is the same. Why? -because it is a relative measure, not absolute. F2.8 on a Lumix LX3 allows the same illumination of sensor as PL 25/1.4 set to F2.8, the same as Canon 50/1.4 set to F2.8 !!!

This is wrong. The f-number dictates the amount of light per unit area, so all lenses set to f/2.8 will project the same amount of light per unit area onto a sensor behind them. That means put a FF sensor behind a f/2.8 lens it will collect four times the amount of light than wiill a Four thirds sensor behind an f/2.8 lens.

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.

If 'total BS' means 'the truth', yes, it is.

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.

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. That's it, people. It has never meant FF versus 4/3 versus whatever sensor/film size you had in your camera. Just the optical geometry. Easy ? Accordingly , F11 means that this diaphragm /aperture diameter will fit 11 times into the instrument's focal length. It's been like that since the inception of photography in the 19th century.

Frankly, your sarcasm is misplaced. Everyone discussing this knows that. The question is, what is the implication of that fact.

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.

Actually, you don't know how a sensor works at all. It's not a current collecting device, it's a charge collecting device. The precise relationship between the size of various components in a pixel is complex, but on the whole, small pixels do not demonstrate any higher electronic noise than big ones. In any case, the electronic noise is only a very small component of the overall noise in an image, and only really apparent in the hsadows. Most image noise is 'photon shot noise' which is the noise due to the quantum nature of light (i.e. it is not a continuous phenomenon). The more photons you collect, the better the signal to noise ratio. that's why bigger sensors (behind the same f-number lens) display better signal to noise ratio.

The DPR once had a very useful parameter in the camera specification table describing the sensor's photosite in micrometers. there one could easily see that larger Canikons had bigger photosites, something like 8 micrometers vs Olympus's (don't remember precisely) 4.6 or something like that, therefore their light sensitive "transistors" were bigger and could provide higher DC current compared to Olympus's or any other smaller sensor. It is This DC micro current that gives you higher DR and less noise, NOT the size of the sensor. Mind you , if Canon were to put 50 megapixel into its FF sensor it will have a much worse performance for noise and DR compared to their own 16 Mp or whatever on their current offerings. Again it has to do with pixel density (diodes per square mm) and size of the electronic device,it has nothing to do with 36x24 mm. If Olympus were to put only 3 Mp into their 4/3 sensor it would be the same of better than any Canikon you know in terms of noise and DR, but then you would complain about the low resolution, yeah, right !

Sorry, the stuff about 'DC micro current' is completely wrong. Sensors measure charge not current.

The megapixel race is for stupid consumers and marketing boys/ploys, it has nothing to do with photography. I am totally against it. I don[t need even 16 MP on my EM1 and would love to see a new Olympus sensor with 10 or even 8 MP but with a higher quality sensor properties. That's it.

In the mean time : kudos to Olympus engineers for designing their fine lenses !

thank you for reading and now I will retire to my morning coffee.

I suggest that over your cup of coffee you learn something about optics and sensor technology, so that you can get it just a bit right next time.

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