The Tamron 18-250mm F/3.5-6.3 AF Di-II LD Aspherical (IF) Macro is currently the largest ratio zoom lens available for APS-C DSLR cameras, with a 13.8x zoom ratio. When mounted on a Canon EOS APS-C format DSLR the lens has the same coverage as a 29-400mm zoom would have on a full frame 35mm camera. Note that this is a Di-II series lens, which means it is only designed to cover the area of an APS-C sensor. While the lens can be mounted on any EOS SLR camera, on full frame models it shows significant vignetting at all focal lengths.
To improve image quality the lens uses two LD (low dispersion) elements, one AD (anomolous dispersion) element and two hybrid aspherical elements.
Considering the wide zoom range the lens is remarkably compact as can be seen in the comparision image below.
|Angle of View||75° 33' - 6° 23' (APS-C size equivalent)|
|Lens Construction||16 elements / 13 groups|
|Minimum Focus Distance||0.45m (17.7") (entire zoom range)|
|Maximum Mag. Ratio||1:3.5 (at f=250mm, MFD 0.45m)|
|Overall Length||84.3mm (3.3")|
|Maximum Diameter||74.4mm (2.9")|
|Diaphragm Blades||7 blades|
|Standard Accessory||Flower-shaped Lens Hood|
|Compatible Mount||Canon AF, Nikon AF-D, Pentax AF, and Sony (Konica Minolta)|
The lens aperture varies with focal length as follows:
The Tamron 18-250mm F/3.5-6.3 has a zoom lock at the 18mm position to prevent the lens from extending while being carried.