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Message: <blockquote data-quote="alanrharris53" data-source="post: 1737919" data-attributes="member: 61894">Thanks everybody.I managed to get out yesterday and took some pictures with both the Tamron and the Sigma.  Not very scientific but trying to reflect the real conditions in the field.First went and took some bird photos at a local spot where they are fairly tame. Overall in good light there seemed to be little difference in the image quality between the two lenses at 500mm f8. (As mentioned above the Tamron is also a lot sharper at f8 than wide open.)  If anything the Tamron apeared very marginally sharper - but I took about 200 photos and it was only noticable on one or two shots.The difference in reach at 500mm was not noticable in actual use.  Although I still think it might be an issue when taking birds at a greater distance than I was shooting yesterday, where you have to crop more.The AF is a lot faster with the Sigma too.  I managed to grab a couple of black headed gulls in flight which I couldn't manage with the Tamron. I haven't posted them as they are not great shots, but convinced me the potential is there.I then went to take some picture of the deer in the local park.  As I got there it turned very dark.  And after taking about another 200 shots it started to snow!  So I didn't get chance to compare with the Tamron but I know from experience that the photos I was taking at slow shutter speeds with the OS on would have been impossible with the Tamron.Overall intial impressions are that the OS and AF are both showing the advantage I was looking for in moving over to the Sigma.  But the Tamron is still a good lens in good light and may well be marginally sharper at 500mm.I will keep both lenses for a while and do some more comparisons but initial shots here if you are interested...<a href="http://www.flickr.com/photos/alan-photos/sets/72157623467395414/" target="_blank">http://www.flickr.com/photos/alan-photos/sets/72157623467395414/</a></blockquote>

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