Compare lenses

Pentax HD DA 20-40mm f/2.8-4 ED Limited DC WR vs Tamron SP AF 17-50mm f/2.8 XR Di II LD Aspherical (IF)

The Pentax HD DA 20-40mm f/2.8-4 ED Limited DC WR and the Tamron SP AF 17-50mm f/2.8 XR Di II LD Aspherical (IF) side by side, computed from this guide's catalogue.

Which to pick

Pick the Tamron SP AF 17-50mm f/2.8 XR Di II LD Aspherical (IF) if you want more reach (to 75mm equivalent), a wider view (from 26mm equivalent) and a fit on more cameras (51 against 20 in this guide). On these specs the Pentax HD DA 20-40mm f/2.8-4 ED Limited DC WR has no clear advantage: choose it if the price, the handling or a lens you own decides it.

Still torn? Ask the guide about the Pentax HD DA 20-40mm f/2.8-4 ED Limited DC WR and the Tamron SP AF 17-50mm f/2.8 XR Di II LD Aspherical (IF)

Specs side by side

Rows that differ are in full colour; the better value is marked where one is better by any measure.
Spec	Pentax HD DA 20-40mm f/2.8-4 ED Limited DC WR	Tamron SP AF 17-50mm f/2.8 XR Di II LD Aspherical (IF)
Maker	Pentax	Tamron
Focal length	20-40mm (zoom)	17-50mm (zoom)
Full-frame equivalent	30-60mm on APS-C	26-75mm on APS-C
Maximum aperture	f/2.8-4	f/2.8
Made for	APS-C	APS-C
Mounts	Pentax K	Canon EF, Nikon F, Pentax K
Stabilised	no	no
Autofocus	yes	yes
Zoom range	2.0×	2.9×more range
Weight	283 g	not listed
Cameras it fits	20 in this guide	51 in this guidefits more cameras

Focal range, in full-frame terms

Pentax HD DA 20-40mm f/2.8-4 ED Limited DC WR: 20-40mm on APS-C, like 30-60mm.

Tamron SP AF 17-50mm f/2.8 XR Di II LD Aspherical (IF): 17-50mm on APS-C, like 26-75mm.

Aperture

Pentax HD DA 20-40mm f/2.8-4 ED Limited DC WR: f/2.8 wide open.

Tamron SP AF 17-50mm f/2.8 XR Di II LD Aspherical (IF): f/2.8 wide open.

Each opening drawn to scale against f/1.4: a smaller f-number lets in more light and blurs the background more.

Field of view

How wide each sees, at each end, on the sensor it was made for.

Cameras they fit

20 cameras in this guide take both, so either works on the same body. In all, the Pentax HD DA 20-40mm f/2.8-4 ED Limited DC WR fits 20 and the Tamron SP AF 17-50mm f/2.8 XR Di II LD Aspherical (IF) 51.