I am using a Panasonic Lumix G Vario 35-100mm F.28, a MFT telephoto lense.

I am learning about photography by reading articles and reviews and in one review it was mentioned there is a great portrait lense, namely the Panasonic Lumix G 42,5mm F.17, also a MFT lense.

I learned a bit about sensor size (full frame, ASP-C, MFT, ...) and the relationship of f#, focal length and aperture, etc., though I'm still not very fluent to be honest.

Considering that the sensor size is the same (MFT) and that the focal length of the portrait lense 42.5mm is within the range of my telephoto lense, I ask myself why would I want to buy the portrait lense then?

The different I see is the f.#, but what does that mean? Could someone explain to me in simple words please? And it would be nice to have some examples (on some articles they let me see what the difference is, but not sure if one can show a difference of F17 and F28?).

I am using a Panasonic Lumix G Vario 35-100mm F/2.8, a MFT telephoto lens.

I am learning about photography by reading articles and reviews and in one review it was mentioned there is a great portrait lens, namely the Panasonic Lumix G 42,5mm F/1.7, also a MFT lens.

I learned a bit about sensor size (full frame, ASP-C, MFT, ...) and the relationship of f#, focal length and aperture, etc., though I'm still not very fluent to be honest.

Considering that the sensor size is the same (MFT) and that the focal length of the portrait lense 42.5mm is within the range of my telephoto lense, I ask myself why would I want to buy the portrait lense then?

The different I see is the f.#, but what does that mean? Could someone explain to me in simple words please? And it would be nice to have some examples (on some articles they let me see what the difference is, but not sure if one can show a difference of F/1.7 and F/2.8?).