Originally posted by normhead We don't know what the 18-135 image taken at the same time would look like. Given that Tess' K-5 produced an identical image to one produced by my K-1 both using the DFA 28-105, I'm really hesitant to even view comparison images if not taken at the same time. You can determine form solo images if you might like the lens, but to say it's better or worse you have to have direct comparisons.
I get where you're coming from, Norm... and yet...
You generally tend to want proof of opinions rather than just the opinions themselves. And proof is good, for sure. But opinions on their own still have value, especially if the source has proven themselves to be generally level-headed, knowledgeable and experienced. They have even more value if a number of other folks have similar opinions, and more still if those sources are also good.
I've known you for long enough on these forums that if you say - for example - lens A is sharper than lens B in the borders until f/8, I can be pretty confident that's the case, with the only obvious variable being copy variation for each lens. If you show me evidence in the form of your photos, that's great - but if you don't, I can still take your opinion as a valuable ingredient in reaching a conclusion. And I can place that same confidence in a number of our other members, @Rondec amongst them.
Then, there are folks I've had less involvement with whose opinions I still value, but I might want to research a few additional opinions for confirmation.
Next, there are opinions from those I've had little or no experience of in the past... and those are still potentially valuable to me, but I look for far more confirmation from other sources.
Finally, there are opinions from some folks that I'll take with a huge pinch of salt, or might bypass altogether for a variety of reasons. That's fairly rare, but not at all unheard of.
I guess what I'm saying is, an opinion needn't be indelibly tied to proof or supporting evidence to be valuable. There's an element of trust required that opinions have potential value, IMHO, beyond which it's on each of us to validate them as required through our own research. The burden of proof, if we want it, is actually on us - not the guy or gal with the opinion (at least, that's how I see it). The final validation, of course - our conclusion, the opinion that matters most - is formed from our own testing and / or real-world shooting. And that, in itself, can differ hugely due to subjectivity... Hence why lots of members love and post great photos taken with the DA20-40, yet I remain luke warm about it; also, why I tried two copies of the 18-135 at different times, returning both because it just didn't suit
me
Final comment... I have a whole bunch of lenses. I never once took the exact same photos at the same time with each and every one of those lenses to compare and rank them. Yet, from varied experience in shooting them, I can say what I like and dislike about most of them, and have formed opinions as to why some are (based on my subjective views and preferences) "better" than the others. Ask me to prove those opinions? In most cases, I'm screwed. I could show you photos taken with each lens, but they're nothing like side-by-side comparisons. Still, I have a good idea how each of the lenses performs in different situations...