Amateur Photographer - UK (2020-03-28)

subscribe 0330 333 1113 I http://www.amateurphotographer.co.uk I 28 March 2020 15

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4

Blade formation

The aperture hole is made bigger or smaller by blades

opening and closing in a circle formation, however as

you’ve probably noted if a circle is made up of straight lines

then it’s not a completely round circle. The more blades

your aperture ring has the more circular it will appear,

hence making the out-of-focus area creamier and more

desirable. How many blades your aperture ring has will

vary from fi ve upwards. The bokeh effect from fi ve blades

will appear like an undesirable pentagon in the background

of your image so although the cheaper prime lenses might

seem like a good deal there is a reason they are cheaper.

Make sure you look at this aspect when purchasing a lens,

and weigh up the price vs quality conundrum.

5

D i ffr a c t i o n S O S

Diffractionis anopticaleffectcausedbylightrays

spreadingwhentheypassnexttotheapertureblades.

Selectinga verynarrowaperturetocreategreater

depthof fieldalsomakesthein-focusareasof the

imagevisiblysofter.Diffractionactuallyoccursat every

aperture,butitseffectis mostvisibleat smallsettings

becausea largerproportionof thelighttravelscloseto

theapertureblades.Foranygivensensorsize,the

degreeof diffractionblurringdependsonthef-number,

regardlessof thelensbeingused.Butwithsmaller

sensors,youshouldchooselargerf-numberstoavoid

itseffects.Forexample,f/8onMicroFourThirdsgives

thesameeffectasf/10onAPS-C,orf/16onfull

frame,in termsof depthof fieldanddiffractionblurring.

f/

1 2

f/

At f/22 diffraction starts to soften the image detail...

At f/11, however, the detail in the image is crisp and sharp

Both these images

have been shot at a

shallow f/1.8, however

the background in the

image here is further

away hence being

more out of focus

The blade formation

of your aperture

ring will affect how

the bokeh blurred

shapes behave