Example: How good is Sigma 70-300mm F/4-5.6 DG Macro Lens
The question shows that some basic research has been done, and it's not one of those "shop for me!" questions we all love so much. But, essentially, it is "Can you give a quick review of this lens, please?"
Are such questions on-topic / "constructive"?
Yes, assuming they are asked and answered appropriately.
One thing we aspire to is a collection of well supported answers. This means supplying either references or considered experience. A good way to elicit such answers is to pose these questions in the form
"I've done the research, I've read the reviews, but how does this product really perform when you're using it for X (or want to achieve Y) and how do you know that?"
That, I think, shows how this class of questions fits within our framework and indicates how we can add extraordinary value compared to many other Q&A or review sites.
People are going to come to our site expecting to find information about equipment. This is the logical place to ask such questions.
That doesn't mean that we should accept such questions, but surely it should give us pause to think about what are we offering?
Choosing equipment is a major part of photography, and to ignore this would make our site less than it could (should) be. Of course, diluting our site with off-topic, un-answerable or too-localised questions would also be detrimental.
If we just point people to google, they don't know which reviews are trustworthy. I.e. there is too much noise.
Perhaps we could solve the noise problem by having pointers to good review sites?
For example, would it help to have a question which solicits a list (or index) of trustworthy review sites? Then when someone asks a review-type question, we could close their question and point them to our "index" question?
Fortunately, @Eruditass has already asked this question, which seems to be exactly what we need.
My personal opinion on recommendations is that it is incredably difficult to ask them in a manner that would be relevant to future visitors, i.e. it wouldn't fall foul of:
This question is unlikely to ever help any future visitors; it is only relevant to a small geographic area, a specific moment in time, or an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet.
(emphasis mine; And yes, that really is the closure description for "Too localised")
Or even:
This question is not a good fit to our Q&A format. We expect answers to generally involve facts, references, or specific expertise; this question will likely solicit opinion, debate, arguments, polling, or extended discussion.
(i.e. "Not constructive")
There is no reason why it couldn't be subject of chat in the chat room; and there are ways of asking a question about recommending gear in a more quantitative manner (Things like, "In real terms, what difference in field of view will I get between the Acme 17-40 and the Acme 16-40?".
I think a broad review is probably going to be too subjective and broad to be beneficial, however, I think within a scoped context this kind of question can be quite on-topic. (Which I suppose really means it is on-topic, but without scope it is too broad.) I don't think we can really answer "is lens x a good lens?" but something more like "Will this lens work well for goal x?" is answerable, beneficial and well scoped.
It isn't asking for best (which would be highly opinion based and prone to change over time). It isn't asking for a selection (which would be shopping and prone to change over time), but rather giving:
which can be answered.
Yes, it is still mildly subjective, but I think it falls under good subjective as it is able to be answered with experience and strong points as to how the strengths of the lens are useful to the task at hand.
Personally, I do not think that these questions are on topic or constructive to the site, in the way they are. Anyone looking for a new lens or a lens for a particular subject or shot can do a simple Google search for it and find plenty of unbiased views, and recommendations.
I think these questions are often asked out of laziness.
However, as @whuber says, if they are asked in a more appropriate way to direct the question towards a very specific answer, rather than an an answer that is made up mostly of personal/emotive thought rather than fact, then they would be of more benefit to the community.
