PhotoPlus The Canon Magazine – August 2019

The Canon Magazine 101

astro lenses

Centre Edge Corner

2500

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1500

1000

500

Sharpness

f/1.8f/2.4 f/4 f/5.6 f/8 f/11 f/16f/22

Ir IX 15mm f/2.4

BLACkST oNE £574/$675

A real night owl of a lens, the Blackstone even has

fluorescent engraved markings

esigned in Switzerland

and built in Korea, the

Irix 15mm is available in

Firefly and Blackstone

options. Both are optically

identical but the Blackstone

has a magnesium alloy rather

than plastic casing, four

weather-seals instead of three,

and fluorescent engraved

markings for easy reading

under very dull lighting.

As a manual-focus lens, the

focus ring has a typically

smooth and precise operation

with long rotational travel. It

comes complete with a focus

distance scale that includes

markers for depth of field and

hyperfocal distance at various

apertures. A secondary ring

enables you to lock the focus

ring at any position.

Although lacking autofocus,

the Irix includes the necessary

electronics to operate the

focus confirmation lamp in the

viewfinder, and to control the

aperture from the camera

body. You can therefore shoot

in Program and Shutter

Priority modes, as well as just

Aperture Priority and Manual.

The lens has a separate

petal-shaped hood and a large

95mm filter attachment

thread at the front.

Performance

Image quality is excellent,

with good sharpness across

the whole image frame,

minimal lateral and spherical

aberrations, and well-

controlled distortion.

Vignetting isn’t too bad at

f/2.4, but coma and

astigmatism are pronounced

giving a noticeable and

irregular shape to stars and

other dots of light. Both are

much improved by narrowing

the aperture by an f-stop.

FeATUres

VerdIc T

01

Two aspherical, two

Extra-low Dispersion

and two High-

Refractive index

elements inside.

02

Standard and

nano-structure

‘neutrino’ coatings

are applied.

03

A fine-adjustment

mechanism at the

front of the lens.

04

Engraved markings

for focus distance,

depth of field and

hyperfocal distance

are fluorescent.

05

The mount includes

a gel filter slot.

FeATUres

BUIld & hAndlIng

PerFormAnce

VAlUe

oVerAll

01

02

03

D

2

4

0

–2

–4

–6

Distortion

Canon 16-35mmIrix 15mmSamyang 10mmSamyang 14mmSigma 14mm Tamron 15-30mmTokina

Sigma 14-24mm 11-20mm

Negative results show barrel distortion at the short end of the zoom,

positive indicates pincushion distortion at long end of the zoom range

-2.39 -2.15

-3.62

-4.36

s with our other lab-tests in this round-up, we’ve

concentrated on the amounts of distortion for zoom

lenses at their shortest focal lengths, where they more

directly compete with the prime lenses on test. The results

themselves look like a mixed bag but, by necessity, they’re

based on shooting test charts at a very close range, due to their

physical size. In ‘real-life’ shooting, especially for landscapes

and the night sky, distortion is minimal in all cases.

DISTorTIoN

Lab-results don’t tell the whole story when it

comes to barrel distortion

A

-2.87

-4.99 -4.50

-2.31

04

05