I know you kind of said this in a previous post but just sure I want to understand. Is what I am about to say correct in your opinion:
The Tamron at f8 and the Sigma at f6.3 have similar image quality? (Does one have an edge?)
The Sigma is sharper than the Tamron when both are at f6.3. (seems clear from the woodpecker shots and the bullfinch)
Now some questions:
When both are at f8 which has the edge?
Which has better IS?
Which would you consider a better all around lens? Specifically, does the increased weight of the Sigma make it more difficult to handhold and keep steady? Or do you find that the increased weight is offset a bit by the ability to shoot at f6.3 instead of f8 and therefore have a faster shutter speed in the same lighting?
The Sigma at f6.3 is approximately as good as the Tamron at f8
At f8 the Sigma is better (as expected)
The stabilization of the Tamron is supposed to be a little better (around half a stop) but the Sigma OS seems to take less time to stabilise the image.
I find the weight of the Sigma to help me hold it steady more easily BUT I have been handling much heavier lenses before (including the 400mm 2.8 and 600mm f4) so I am used to hand holding heavier lenses.
I find the Sigma a better all-around lens due to:
1. Better overall sharpness and less chromatic aberrations (especially open wide)
2. Better AF
3. Better weather sealing
4. Better overall build (feels more sturdy, much closer to the Nikon primes)
5. Supports push/pull zooming
6. AF with the 1.4x
7. Custom modes setting with the dock which allow for much better BIF shots (my settings are outlined below)
Normal mode
------------------
Focus: Standard
Focus limiter : 10m to infinity
OS setting : Standard
C1
----
Focus: Drive speed-priority
Focus limiter : 20m to infinity
OS setting : Dynamic
C2
----
Focus : accuracy-priority
Focus limiter : 30m to infinity
OS setting : Moderate
The Tamron is also a fantastic lens and I will surely keep it until I test the contemporary version of the Sigma.