Originally posted by Digitalis Canon designs their lenses so the camera body will communicate to the lens and adaptively "learn" how to focus accurately with it* - this is why third party lenses have a higher incidence of issues related to AF accuracy**. Sigma and other third party manufacturers cannot copy this due to patent laws.
I don't want to comment on Sigma and Canon. This is a forum for Pentax users and the OP has a problem with a Pentax camera.
Pentax AF protocols have been known for a long time and there is zero evidence that third-party manufacturers have any difficulty to replicate the lens behaviour as required.
Again: Professional photographers use Sigma lenses. They would not do that if it implied any kind of compromise.
Originally posted by Digitalis None of my sigma lenses had AF that was anywhere near accurate on any of my pentax camera bodies out of the box***.
This is unfortunate, but does not prove that Sigma has difficulty replicating AF protocols.
It also, BTW, does not prove that Sigma QC is worse than Pentax QC (or any other lens maker's QC, for that matter).
Your personal experience only means something in terms of a systemic effect, if it is backed up by other similar experiences, adding up to statistical significance.
Originally posted by Digitalis So my opinions are invalid because i'm incapable of making any objective statements on third party lenses.
No, your opinions are not invalid at all.
However, your personal experience does not constitute absolute truth. It is just a single data point. Nothing more, nothing less.
Originally posted by Digitalis I dare you to buy as many lenses as I have and maintain an objective view on lens makers.
I'm not sure what the challenge is, but one thing seems to be clear:
Despite your apparently almost unlimited funds for photography (with several camera systems and extremely expensive lenses such as from Leica), you choose to have multiple lenses from Sigma. You actually own more Sigma lenses than I do. So despite your unfortunate history with AF accuracy, you are still holding on to these lenses.
From this I conclude that
- at least after AF calibration, AF accuracy must be at least acceptable, and
- optically these lenses must be very good, if not exceptional.
But all we hear from you thread after thread is how idiotic Sigma designers are and how terrible Sigma AF is, etc.
It just doesn't make sense. Now, if you were complaining about your other lenses just the same, I'd understand. But you seem to have an axe to grind with Sigma in particular. Why don't just sell all that inferior gear and avoid being annoyed?
Originally posted by Digitalis I think I'm justified in being more than a tad annoyed with sigma.
You are entitled to be annoyed about whatever you want and you are also entitled to continue to be annoyed even though you could just end it all by selling this annoying gear (instead of buying more Sigma lenses, as you just recently did).
What you cannot expect is to spread unfounded pejorative rumours about Sigma technology without people objecting to it.