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We’re clearing up another bit of confusion that comes up with lenses and crop factor!

Tony tFuntek was wondering why the actual aperture diameter of his 25mm f1.8 micro 4/3 lens is different than the aperture diameter of his 50mm f1.8 full frame lens.

Here’s Tony’s question:

Here is the question that I have not found an answer…I shoot with a full frame camera and I also use a M4/3’s camera when portability is an issue. Why is is the aperture physically larger on my full frame 50mm f1.8 than my 25mm F1.8 M4/3’s lens ? The same is true on my 45mm f1.8 M4/3’s lens. How can they both be f1.8 with 2 different size openings? It would make sense the M4/3’s lens is passing less light through. Your thoughts and thank you for all your videos. Tony

There’s two issues that I discuss in the video here that clear this up.

The first is where the f number comes from, and the second is false equivalencies being drawn between lenses that are inherently different.

Micro 4/3 cameras have a crop factor of 2, which means if you put a 25mm lens on a micro 4/3 camera, and put it right next to a full frame camera with a 50mm lens, and take the same picture, compositionally those pictures will be the same.

That leads to some people thinking that a 25mm micro 4/3 lens is the same as a 50mm full frame lens, which is not true. It is in fact a 25mm lens.

Once we realize that we can deal with where the f-number comes from, which involves a little math.

Watch the video to learn where f-numbers come from and why f1.8 is different on different lenses.

Your camera is an amazing tool, but it’s no good to you if you don’t know how to use it!

If you want to take control of your camera and use it to take amazing photos like a pro, check out my Guide to Shooting in Manual Mode video course.