I'm stewing over the Sigma C and Tamron 150-600mm's and interested in your thoughts on IQ having tried both. I've read a number of reviews saying the Tammy is sharper at the long end, would you say this is true and if so is it easily noticeable or only if you're really scrutinising them?
My thoughts are that the sigma is the better lens but there's not enough of a photo pool out there to get a true 'feel' for the lens, whereas I've seen enough shots from the Tammy to get an idea of what I'd be getting
Hi 'snerkler' here are my (long winded) thoughts for what they are worth.
I have know of a few people who have owned both who think that the Sigma is slightly sharper at the long end whereas folks who have looked at test results think that the Tamron shades it at the long end. To be honest having used both I have always said there is very little in it either way with real results and in the field you would be hard pushed to see a lot of difference. One thing I am fairly certain about is that the Sigma AF's better in situations where contrast is low. The sigma also takes a 1.4x tc fairly well if you have a Camera that will AF at f8.
There are certain things with the Sigma which I think makes it a better lens.
Here are some cons on the Sigma lens itself:
Better focus limiter choices
Two OS (VR) modes inc one for panning
2 hard lock and 6 soft locks on the focus range (150 hard, 180, 200,250,300,400,500,600 hard)
An easily removable tripod foot to lighten the load if hand holding - with a supplied collar to protect the ring where the foot is removed.
There are also some useful utilities with the Dock if you buy one:-
Down load any future firmware direct to the lens.
Micro adjustments can be made to the focus for 16 ranges (4 focusing distance ranges in x 4 shooting distance ranges) in total for zoom lenses.
Ability to turn full time Manual focus on or off
AF speed selector ( Speed, standard, or Focus priority ) for some reason the default is 'standard' but should be set to 'focus' ASAP IMO
Specify your own Focus limiter distance range
Choose between 3 OS settings .
You can save any combo of the above to C1 or C2 and switch between either or the off position on the lens.
At the end of the day both lenses are good value for money and I doubt anyone would be displeased with either one unless they are comparing with more expensive prime lenses. Best of luck whichever you choose