I already have the Sony 70-400mm G lens for the above camera. However I am looking to get a longer lens. I do have a 3rd party 2x converter, but this will only work with manual focus (not good for sports or action - e.g aircraft, etc). I have scoured the internet but as yet only found 1 lens - Sigma 150-500mm f5/6.3 HSM DG OS - in Sony A fit. It is from a reputable store and according to 'their' description: 'Average condition telephoto zoom lens for use with A mount SLR's. It's pretty spot on condition wise with light signs of general use, however it's been marked down a touch as there's a small spot of fungus on a central element unfortunately. This won't affect it's use but is worth mentioning. Comes unboxed with caps, hood and a 6 month guarantee'. It's priced at £449.99. I would welcome thoughts (pros and cons) on this lens as opposed to my G lens. Also if anyone knows where else I might be able to get the 200-600mm Tamron in Sony A fit, which would be better as it is longer. I am reluctant to go down the eBay route, or upgrade to Sony E mount, as I already have a number of lens in A mount fit and do not particularly want to 'start again', or trade all of my Sony gear to another make. Thanks in advance.