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Message: <blockquote data-quote="RJL2005" data-source="post: 1507066" data-attributes="member: 37514">I have seen the same effect with my 100-400.But it also happens with my Sigma 500 4.5 when the background is as described (close to subject and has sharp edges) This was taken with the bird in among branches:<a href="http://www.birdforum.net/gallery/showphoto.php/photo/244574/ppuser/37514" target="_blank">http://www.birdforum.net/gallery/showphoto.php/photo/244574/ppuser/37514</a>1/250 f5.6 iso250.This one with a clearer background:<a href="http://www.birdforum.net/gallery/showphoto.php/photo/244645/ppuser/37514" target="_blank">http://www.birdforum.net/gallery/showphoto.php/photo/244645/ppuser/37514</a>1/350 f5.6 iso250It is not a question of getting closer to your subject, these were taken from a hide, using a beanbag (the lens has no IS) and at a distance of between 15 and 30ft. It appears to me to be a function of the sharp edged BG and the lens aperture. I imagine if you could open up wider than f5.6 it would be greatly lessened, along with the bank balance<img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile    :)" loading="lazy" data-shortname=":)" /></blockquote>