Pentax HD Pentax-DA 20-40mm f/2.8-4 ED Limited DC WR Specs & DoF

20–40 mm

Focal length

f/2.8–4

Maximum aperture

70°–39°

Diagonal angle of view (APS-C)

APS-C

Designed for

2.0×

Zoom ratio

Specifications#

Brand: Pentax
Model: HD Pentax-DA 20-40mm f/2.8-4 ED Limited DC WR
Lens type: Standard zoom
Focal length: 20–40 mm
Maximum aperture: f/2.8–4
Image circle: APS-C (23.5×15.6 mm)
Mount(s): Pentax K
Projection: Rectilinear
Lensfun correction profile: Yes — distortion/vignetting/TCA

Equivalent focal length on different cameras#

Field of view and depth-of-field equivalence when this lens is used on bodies with different sensor sizes (natively or via an adapter).

Camera format	At 20 mm	At 28 mm	At 40 mm	Equiv. aperture (DoF)
APS-C	30 mm · 70°	42 mm · 53°	60 mm · 39°	f/4.2
APS-C (Canon)	32 mm · 68°	45 mm · 51°	64 mm · 37°	f/4.5
Micro Four Thirds	40 mm · 57°	56 mm · 42°	80 mm · 30°	f/5.6

Depth of field & background blur#

Computed on its native APS-C format (CoC 20 µm). “Blur @2 m” is the size of an out-of-focus point at infinity, as a percentage of frame width, with the subject at 2 m — a simple bokeh index. Full table: 20 mm f/2.8 on aps-c.

Focal	Aperture	at 1 m	at 2 m	at 5 m	at 10 m	Hyperfocal	Blur @2 m
20 mm	f/2.8	27.3 cm	1.17 m	12.7 m	∞	7.32 m	0.3%
20 mm	f/4	39.8 cm	1.82 m	190 m	∞	5.13 m	0.2%
20 mm	f/8	89.9 cm	7.74 m	∞	∞	2.58 m	0.1%
28 mm	f/2.8	13.6 cm	56.2 cm	3.95 m	27.1 m	14.3 m	0.6%
28 mm	f/4	19.6 cm	81.9 cm	6.58 m	2.0 km	10.0 m	0.4%
28 mm	f/8	40.3 cm	1.86 m	643 m	∞	5.04 m	0.2%
40 mm	f/2.8	6.6 cm	27.0 cm	1.75 m	7.71 m	29.3 m	1.2%
40 mm	f/4	9.4 cm	38.7 cm	2.58 m	12.8 m	20.5 m	0.9%
40 mm	f/8	18.9 cm	79.6 cm	6.34 m	379 m	10.3 m	0.4%

Handheld & night-sky limits#

NPF assumes typical 20–24 MP sensors (≈6 µm pixels on full frame, ≈3.9 µm on APS-C, ≈3.3 µm on Micro Four Thirds).

Body	Min. handheld shutter (longest focal)	500 rule at 20 mm	NPF at 20 mm, f/2.8
APS-C	1/60 s	17 s	11 s
APS-C (Canon)	1/60 s	16 s	10 s
Micro Four Thirds	1/80 s	12 s	10 s

Compatible cameras#

Bodies in our database with a native Pentax K mount. Full-frame bodies switch to an APS-C crop with this lens.

Adapt it to other systems#

Sony E-mount Canon RF Nikon Z Fujifilm X-mount Micro Four Thirds L-Mount Canon EF-M Fujifilm G-mount Hasselblad XCD Nikon 1 (CX)Pentax Q Samsung NX Canon EF Nikon F

Similar lenses#

Pentax HD Pentax-DA 18-50mm f/4-5.6 DC WR RE f/4–5.6
Pentax smc Pentax-DA 18-55mm f/3.5-5.6 AL f/3.5–5.6
Pentax smc Pentax-DA 18-55mm f/3.5-5.6 AL II/L/WR f/3.5–5.6
Pentax smc Pentax-DA L 18-50mm f/4-5.6 DC WR RE f/4–5.6
Sigma 18-125mm f/3.5-5.6 DC f/3.5–5.6
Sigma 18-35mm f/1.8 DC HSM [A] f/1.8
Sigma 18-50mm f/2.8 EX DC f/2.8
Sigma 18-50mm f/3.5-5.6 DC f/3.5–5.6
Pentax smc Pentax-DA 17-70mm f/4 AL [IF] SDM f/4
Sigma 17-50mm f/2.8 EX DC HSM f/2.8
Sigma 17-50mm f/2.8 EX DC OS HSM f/2.8
Tamron AF 17-50mm f/2.8 XR Di-II LD (Model A16) f/2.8

Frequently asked questions#

Is the Pentax HD Pentax-DA 20-40mm f/2.8-4 ED Limited DC WR full frame?

No — it is designed for APS-C sensors. On a full-frame body it vignettes or triggers crop mode.

What is the Pentax HD Pentax-DA 20-40mm f/2.8-4 ED Limited DC WR equivalent to on APS-C?

Its focal length is already the real value for APS-C: 20–40 mm frames like 31–61 mm on full frame.

What is the Pentax HD Pentax-DA 20-40mm f/2.8-4 ED Limited DC WR good for?

As a standard zoom it suits everyday shooting, travel, events and walkaround use.

Sources & licences#

Lensfun lens database — CC BY-SA 3.0