The depth of field, aperture, etc...

My first class was very interesting. I experimented the depth of field for the first time. Before , I realized blur background but I didn't know why. Now I can control it. Thank you.

These are my first photos that I can control my effect:

[ISO 400, 55.0mm, f5.6, 1/20]

My shutter was slow, but the photo seem to be clear fortunately.

[ISO 400, 43.0mm, f5.0, 1/13]

Mmm, I had to increase the ISO to have an higher shutter speed.

[ISO 400, 29mm, f4.5, 1/50]

Due to my low focal length, I need to be very close. For flowers, I was too shy to be at 30 cm. Ahah