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

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gsergei
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A reminder for some memebers as to what the F stop is all about.
9 months ago

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. 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 !!!

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.

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.

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.

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 !

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.

Photo amen to all of you.

-- hide signature --

Sergei,
Calgary.
www.alberta-photo.com

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