What are the 4 factors that determine the bokeh of photo?

"If you buy a fixed focal length lens, you can take wonderful bokeh photos ;) "

I think many people have heard the above "devil's advocate" when they were camera beginner.
I am no exception.
At the time I had only used zoom lenses, the above phrase swirled around in my head.

In conclusion, I later bought some prime lenses.
Before mentioning that, in this post I would like to review the thing called bokeh in photography.

The 4 factors that determine the bokeh of photo

The four factors that determine the bokeh of photo are as follows.

Factors Strong bokeh Weak bokeh
F value Small Large
Focal length Long Short
Shooting distance Near Far
Distance between subject and background Far Near

Let's look at them in order.

* Below, the sensor size of the camera used is Canon APS-C, and the focal length described is the actual focal length.

F value

First, let's compare by F value.

22mm F222mm F2.

22mm F822mm F8.

I shot in Av mode with the same composition.
Look to the background bokeh, the former with a small F value has a larger bokeh.

Focal length

Next, let's compare by focal length.

135mm F2.8135mm F2.8.

22mm F2.822mm F2.8.

I adjusted the F value to 2.8, this is open F value of 135mm lens.
I tried as much as I could to get the composition right, but if you look closely, it's out of focus :}
Look to the background bokeh, the former with a longer focal length has a larger bokeh.

Shooting distance

Next, let's compare by shooting distance.

22mm F222mm F2, near.

22mm F222mm F2, far.

The settings on the camera side are exactly the same, and I changed only the shooting distance.
Look to the background bokeh, the former with a near shooting distance has a larger bokeh.

Distance between subject and background

Finally, let's look at the distance between subject and background.

22mm F2

The distance between subject and background wall is so near that it doesn't bokeh much.
In the case of the above picture, it's just a wall, but if the background wall is nice, it may be good to increase the aperture value.
Rather, the front bokeh is large :}

The reason for the opening phrase is the "F value".
Prime lens is simpler in design than zoom lens.
Therefore, it is the opening word because it is easy to make lens with small F value.

So, as a result of the opening phrase swirling in my head, I ended up buying a prime lens...

The story will continue next post. :)

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