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

Started Jan 26, 2014 | Discussions thread
DonSC Senior Member • Posts: 1,032
Re: Um...

Great Bustard wrote:The total light is the total amount of light that falls on the portion of the sensor used to for the photo during the exposure: Total Light = Exposure · Effective Sensor Area. The same total amount of light will fall on the sensor for equivalent photos but, for different formats, this will necessarily result in a different exposure on each format, since the same total light distributed over sensors with different areas will result in a lower density of light on the larger sensor.

I've always wondered if this were really true. For sure it's true if you mount the SAME lens on cameras with different sized sensors. But what if the lens creates a smaller image circle? A lens isn't a tube. A 300mm f/2.8 lens doesn't have to create a FF image circle. It can create a larger image circle or a smaller one. A 300mm f/2.8 m43 lens which creates an image circle with half the diameter of a 300mm f/2.8 FF lens will deliver the same amount of total light to the sensor. While the area will be smaller the density of light will be higher.

Isn't this what the speed boosters do?

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