Until a few weeks ago I used the lens of my EOS 600D and so on a crop camera. The images were sharp even at maximum aperture and maximum focal length - really sharp. In birds, I could make out the smallest details in the feathers, the quality was only bad if I had to either work with very high ISO values or if the exposure time is set too long. But clearly: this has nothing to do with me the objective, therefore could not have been bigger my enthusiasm about the Bigma.
Recently I then switched to full-frame (6D), I could really test the combination of Sigma 50-500 and camera only on holiday in Sardinia, where I got on the Sinis peninsula flamingos in the wild before the lens. The camera monitor everything in the green area, in the evening when I looked at the pictures on the laptop, I almost despaired. How could it be that almost all the shots seemed blurry and muddy? Photographed I had largely with open aperture and using a tripod (and exclusively in RAW format).
In order not to exceed the scope of this review: I was already on the verge of the Sigma to sell and give the new Tamron 150-600 a chance. But what bothered me: the Sigma has the relatively minimum focal length of 50 mm of course a much wider field of application and it will save you the occasional change of the lens - just at the small format camera.
And in the end is a change not necessary because following two measures have led to a significant improvement in image quality, so that I (if not more enthusiastic as at my old 600D) agree with the focus also on the 6D satisfied:
First - slightly dim and operate with maximum aperture 8.
Secondly - the lightweight carbon fiber used by me until then (or its successor) was funny enough, shortly after my return from vacation in a photo magazine at KB cameras through because the vibrations were too strong here. Interesting, I did not think that the difference CropScience and KB-camera is so clear.
As a result, I am indeed amazed why a lens delivers on a crop camera even when Aperture 6.3 incredibly sharp images, in a small format camera then but only from an aperture of 8. And quite clear: at aperture 8 has with you the ISOs already otherwise go upstairs than in Aperture 6.3, therefore this can be for some people already have a knock-out criterion - despite better noise performance in full-frame area.
But at the moment I'm staying with the Sigma and will not convert to the Tamron. Firstly, because the Tamron is currently not available in any case, on the other hand, because I - as mentioned above - appreciate the comparatively short minimum focal length.
Conclusion: on my 600D imaging performance for my needs was fantastic, at the 6D slightly dimmed good to very good, but not quite as good as I had felt this before.
