Focusing Question

S

sladen

Active member
Hey Guys, Just got a Tamron 28-75mm lens for my Canon 60D and doing some thorough testing (apparently this lens has been known to have some QC issues).

Something I've noticed is that if I focus on a subject at 75mm and then zoom out a bit, say to 45mm, the focus becomes a bit off.

Is this a natural phenomenon with a telephoto zoom lenses like this one, or is this considered a defect and therefore I should think about returning the lens?
 
Your lens is probably varifocal.

With parfocal lenses, you'd probably find it could be an issue with the back focus/back flange, but with cheaper zooms (particularly still zooms) it's more likely that they're varifocal - they're designed for stills where it's likely that you'll be refocussing after zooms anyway and if you aren't then the auto-focus would correct it.
 
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