Tamron AF 18-250 mm f/3.5-6.3 Di II LD Aspherical (IF)
3. Build quality
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Moreover, the following chart shows that neither the dimensions nor the weight of the tested lens are much different from those of other instruments with similar parameters.
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The build quality is typical for the Tamron lenses of this class. If you have had any experience with other models from this manufacturer, like a 17-50 f/2.8 or a 18-270 VC, you will clearly see that it’s the same quality level – perhaps not the highest one, because rubber elements dominate the outside part of the barrel, but also not the lowest one, because in some key places we’ve got metal.
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This metal we’ll find in the bayonet mount the lens begins with. Then we see an autofocus mode switch (AF/MF) and the focal lengths scale, next to which is situated a LOCK switch, used to block the lens when collapsed (at 18 mm). What a pity the producer didn’t include the possibility of it working at any focal length, because the lens has a constant “zoom creep” tendency – it is collapsing or extending under the weight of the front element. After the LOCK switch, we’ll find a solid, big and ribbed zoom ring. It’s action is uneven – it moves loosely in the range of 18-70 mm, then more stiffly in the range from 70 to 200mm and again rather loosely in the range of 200 – 250 mm. In consequence, if we put the zoom in a loosely working focal length range, even the slightest lens movement might result in a sudden “zoom creep” and the focal length change. Sometimes it is annoying.
What’s more, it’s not the end of the annoying things. Sometimes the lens transmits to the body a very strange information about the focal length value. For example, while doing distortion test at 35 mm I found with a surprise that in the data, saved in EXIF, I had the 55 mm focal length! A huge difference!
Behind the zoom ring we find a gold strip with the name of the lens, then a manual focus ring with the distance scale marked in feet and meters. The ring could have been bigger and more comfortable and it could have worked less loosely – in the current state we can hardly call its work comfortable and smooth.
The lens ends with a non-rotating filter thread with a diameter of 62 mm, which surrounds the front element. That element, while zooming, extends so far on a telescopic barrel that at 250 mm the lens practically doubles its dimensions.
Inside the Tamron 18-250 mm there are 16 elements in 13 groups. Three of them are made of the low dispersion glass (LD - Low Dispersion and AD - Anomalous Dispersion), and their task is to correct the diagonal and horizontal chromatic aberration. Additionally, in the Tamron we’ll find two hybrid aspherical elements and a circular aperture diaphragm with seven blades which can be closed, depending on the focus, to f/22-40.
The buyer gets both caps and a petal-type lens hood in the set.
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