What is a Guide Number and How do I use it

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This is a very common question that is asked by those who want to get a better flash than the one they already have. Put simply the Guide Number is the output of the flash that can be used to find out the f-stop to be dialed into the camera when the flash distance is [...]

What is meant by 18% gray and how is that number arrived and why?

We know that there are two types of exposure meters for measuring light that the camera uses. One is reflected and the other is incident. What does this mean and how do you use both? The type that is in most cameras is a reflected kind. Incident is the meter that has a dome on [...]