"Frankly, your evaluation criteria aren't as strict as most folks who evaluate lenses."
No, Frankly, your evaluation criteria are too strict. You talk about it later in your post...."how critical MOST people are..."
If you shoot charts, then OK, there are critical differences....In the real world? Hmmm...show me! I shoot with a half dozen pieces of L glass and a DO lens. I know great glass...and I've seen and shot with crappy glass. Evaluation to me is ONLY in the real world.
"That doesn't mean the 150-500 won't produce images that meet your needs, but none of the Sigma n-500mm lenses are "amazing" in my book."
Again, you're reading or wrote a crappy book. There are amazing shots made with Sigma lenses.
"They're quite good, _especially_ for the price- but in terms of pure IQ, they're a distant second to lots of lenses."
Ridiculous...case in point...Sigma 50mm 1.4 compared to Canon and Nikor's offerings.
"That's why comparison is dangerous- once you've seen what really good glass looks like, you'll see the flaws in anything that isn't top-tier."
Whatever
I've been shooting over two decades...opportunities to use some incredible pieces of kit. Glass I could NEVER afford! Whether it's top tier Glass or Body....the shot is definitely made by whoever is behind the viewfinder....not what is in front.
"I've seen lots of great images made with second tier lenses- but they're still not as good as the same image would be with a tier-1 lens."
Really? Now that is interesting and might just prove your point. So, if you could direct me to wherever these shots exist, I'd be glad to check it out. See, my point is this....whoever has a given lens and knows how to use it best, most efficiently and for the best shot at that time....compared to whoever owns Lens B and knows the same amount about his lens, shooting at the exact same location, lighting, subject, etc....
If both shooters are the same caliber....would there be enough subjective difference to determine which lens was which? Maybe...I agree, maybe it could be done....but ONLY on specific type of shots comparing different lenses and their capabilities....IE, Faster shots (Sports, wildlife) vs. Landscape....where one lens may best another. Believe me, I was more than impressed when I got my first piece L glass (70-200 2.8IS) many years back...the most amazing lens I had ever put on my camera....it felt amazing, looked incredible, focused quick and took Awesome Pictures!!! BUT, I've seen shots others have taken with the Sigmas, Tamrons, Niks, etc....even old Olympus and Minolta 35mm film shots that are amazing! Top tier shots do NOT have to be shot with "Top Tier" lenses. That's just not a fact.
"For instance, the Nikkor 80-400VR is a second tier lens. I've taken images with it, I've sold images taken with it, but it'll never beat an image taken with my 400/2.8 except in the rare case that the two stops of light don't bring enough to get a shot from a moving platform."
Completely irrelevant to this conversation...I would NEVER argue that a second tier zoom could compete with a 1st tier prime. That has nothing to do with this conversation!
"99.999999998% of the time, it's images will be visibly worse than those from the prime. "
Really? Not 100%
"If you learn to read MTF charts, you can see it in the charts..." I know how to read MTF charts...
"...otherwise, if you shoot two lenses, you can see the differences in the images."
This isn't about two lenses....this is about lenses from third party companies with the same attributes....focal length, speed, and build....as lenses from C and N.
"Most people aren't that critical when it comes to IQ, or they don't have years of looking at samples from hundreds of lenses to be able to compare."
Precisely, and MOST people aren't pixel peepers...and MOST people are OUR customers
You're correct....MOST people don't look at sample from hundreds of lenses....including me! I have less than a dozen lenses and it's how I have made my living for quite a while now. In fact, I don't know many professional photogs that spend their time doing that....they spend most of their time perfecting shots with the gear they have!
"So, they get a lens, it produces better images than they're used to seeing, and they think everyone who finds fault with it is a lens snob, or that they've somehow gotten a sample that outperforms the optical formula."
I certainly wouldn't argue "Owner's blindfolded ignorance"...or the common need to defent their latest purchase til the death....I see it happen ALL the time, with many different products....Cars, Home theater receivers, cameras, tires, Apple vs. PC....iPhone v Blackberry...it's everywhere, the need to defend one's purchased. I think it's human instinct, especially in this society amongst men...in the old days, we got to defend our homes and ranches, and caves, etc....Now, during the more civil times, the internet forum has become our battle ground
And we lose our competitive edge if we don't somehow appreciate what we have!
I don't know if any of that made any kind of sense whatsoever....but I do agree with you about this. However, i don't think it was the OP's question or intent
He was more curious about pros/cons on buying third party lenses.
"I suspect it's much like wine- I'm impressed with wines I like, but many of them are horrible to a true wine connoisseur, who's experience and palate run circles around mine, and who can say "Oh, if you like that, then try *this*" and produce something a lot better- sometimes better than my ability to appreciate it."
That seems a bit far fetched to me. Good lenses are obvious. The build quality, the optics, when you twist it on and look through the VF for the first time, the speed, the AF, the end result....ultimately, the picture....all very obvious, even to the novice, I would assume.
You are correct in the fact that crappy lenses take crappy pics....
But I don't think that is what this thread is about....the question is whether or not Sigma can compete with the offerings from Canon and Nikon and I totally believe they can. Are they better than Canon? No way! But can they compete and make great shots, ABSOLUTELY!!!! I have a Sigma 1.4 that I paid less than 500 bucks for....I have a Canon 50mm L that I paid almost 3 timest that much for. I'm not sure that difference (in price/performance ration) exists at 2.8 shooting in the same conditions.
J