Digital Photographer - UK (2020-01)

Find your setup’s sweet spot

to achieve pin-sharp shots

Optimise image

quality

Used wide open or stopped right down,

almost all lenses suffer from aberrations

that degrade image quality. Diffraction is the

most common. It’s caused when some of the

wavelengths of light are bent or diffracted as

they pass through the hole in the lens created

by the aperture blades, resulting in a loss of

sharpness. Ultra-wide-angle lenses tend to be

affected more than telephotos, while zooms

are affected more than prime lenses.

Diffraction is often worse at small apertures

because it’s the edges of the aperture blades

that cause light to diffract, and the smaller

the aperture is, the greater the proportion of

the total light wavelengths being diffracted.

At wide apertures, diffraction is less because

the proportion of diffracted light compared to

non-diffracted light is smaller.

Most lenses tend to give their sharpest

results at f8 or f11, so where possible you

should avoid stopping down beyond that.

This ‘sweet spot’ does vary from lens to

lens, so if you’re keen to achieve optimum

image quality, it’s worth testing your lenses

by tripod-mounting the camera and shooting

the same scene at all apertures, in 1/3 f-stop

increments, then comparing the results at

100% enlargement. Using the hyperfocal

focussing technique (see 7) also means you

can maximise DOF at the optimum aperture.

Top

It’s in the detail

shoot at your lens’s optimum aperture

to maximise image sharpness

Above

Find the sweet spot

Most lenses give their sharpest results

at an aperture of f8 or f11

Left

Sharpness adds strength

pin-sharp images are packed with fine

detail and depth

6

10 pRo Ways To use apeRTuRe

Findyoursetup’ssweetspot

toachievepin-sharpshots

Optimise image

quality

Usedwideopenorstoppedrightdown,

almostalllensessufferfromaberrations

thatdegradeimagequality.Diffractionisthe

mostcommon.It’scausedwhensomeofthe

wavelengthsoflightarebentordiffractedas

theypassthroughtheholeinthelenscreated

bytheapertureblades,resultinginalossof

sharpness.Ultra-wide-anglelensestendtobe

affectedmorethantelephotos,whilezooms

areaffectedmorethanprimelenses.

Diffractionisoftenworseatsmallapertures

becauseit’stheedgesoftheapertureblades

thatcauselighttodiffract,andthesmaller

theapertureis,thegreatertheproportionof

thetotallightwavelengthsbeingdiffracted.

Atwideapertures,diffractionislessbecause

theproportionofdiffractedlightcomparedto

non-diffractedlightissmaller.

Mostlensestendtogivetheirsharpest

resultsatf8orf11,sowherepossibleyou

shouldavoidstoppingdownbeyondthat.

This‘sweetspot’doesvaryfromlensto

lens,soifyou’rekeentoachieveoptimum

imagequality,it’sworthtestingyourlenses

bytripod-mountingthecameraandshooting

thesamesceneatallapertures,in1/3f-stop

increments,thencomparingtheresultsat

100%enlargement.Usingthehyperfocal

focussingtechnique(see7)alsomeansyou

canmaximiseDOFattheoptimumaperture.

Top

It’sinthedetail

shootatyourlens’soptimumaperture

tomaximiseimagesharpness

Above

Findthesweetspot

Mostlensesgivetheirsharpestresults

atanapertureoff8orf11

Left

Sharpnessaddsstrength

pin-sharpimagesarepackedwithfine

detailanddepth

6

10 pRo Ways To use apeRTuRe