Originally posted by frank James is right on this one. If you shoot something far away, like a building several hundred meters away, then you compare both, you'll see the 'actual' focal length of this 18250 lens :0 When you focus at close target, the focal length becomes shorter.
If this was the case, wouldn't the size of the object appear to change as you focus from near to infiinity? It seems that this would be a very noticeable effect.
I don't own a 18-250, so I don't know how it operates. I do have a Sigma 100-300 which is internal focus, now I'm going to have to find out if it has this bizarre behavior.
Tom