What is an exact duplicate on Photo.SE?

Question

More and more I see questions getting closed, or getting a lot of closed votes, when in my mind they are not exact duplicates. I'd like to avoid specific examples here, more interested in general philosophy rather than arguing about specific questions.

In my mind, an exact duplicate is just that. Not the exact wording of course, but the same question where the same answer applies. Not a similar question, or a subset of another question but effectively the same question. One that could easily be found by a search of the site and immediately recognized as duplicate.

As Jeff says

One thing I want to be clear about, though, is that duplication is not necessarily bad. Quite the contrary — some duplication is desirable. There’s often benefit to having multiple subtle variants of a question around, as people tend to ask and search using completely different words, and the better our coverage, the better odds people can find the answer they’re looking for. And isn’t that, really, the whole point of this exercise?

Furthermore, it’s OK for duplicate questions to have duplicate answers. While you could argue that the duplicate questions could all be merged into one question with a “master” set of answers, this is kind of irritating from the perspective of the user looking for an answer. Put yourself in their shoes. Instead of finding

Duplicate Question — Duplicate Answer

They have to deal with finding:

Duplicate Question — [closed as duplicate of Question] click here to see answers

"subtle variants of a question" doesn't sound like what we allow here - we seem to me to do is look for the slightest connection with another answer and flag it as "possible duplicate".

There are a few types of questions I often see getting a lot of close votes here lately:

Simple question (with a simple answer) where there is a more general question with longer, involved answers

Sure, the long involved answers will provide enough information, if absorbed, to answer the simple question, but that doesn't make them a duplicate. We should in fact encourage simple questions with simple answers. A recent example was someone asking if shutter speed and film speed were the same thing, related, or independent of each other. That got a lot of close votes as a duplicate of the epic "what is the exposure triangle" question. No one should have to try to read 16 paragraphs of information to get what is effectively a yes/no answer to a simple question.

As Joel says:

For example, if a user asks, “What does the IP address 128.0.1.1/24 mean?” it’s OK to close that as a duplicate of a more general question like “What do IP addresses of the form a.b.c.d/e mean?” But it’s not OK to close it as a duplicate of a twenty-seven page guide to netmasks. That’s the moral equivalent of saying “RTFM.”

So again, just because another answer (to a different question!) does include the answer to a simpler question, being a superset of the needed answer doesn't make it a duplicate.

Simple questions where there is a similar question

These are hard, and I know it's a gray area. But to me, most of these types of questions are often not duplicates, but are often flagged as such:

• Compare lens A vs lens B (Canon) where there is already a Nikon question on the equivalent lenses. There are distinct differences between specific lenses of different manufacturers. The Canon 50mm 1.4 may have horribly slow AF, and the Nikon soft in the corners. Sure there are general principles if they're comparing a prime lens vs kit zoom, but the offerings do differ between brands, and if they are asking a specific question about Canon, I don't feel we have the right to force them to generalize their question if it's Canon they want information on.

• "Compare lens A vs lens B", where there is already a "Compare lens A vs lens C". No comment, but this happens a lot. Should we allow every conceivable combination of lens shopping questions? No comment there either. But A vs B is clearly not A vs C.

• "Is f/4 lens with IS or f/2.8 lens better for sports?" when there is an existing question "Is ... or ... better for travel?" (or wildlife or portraits...). Surely not a duplicate, as different genres of photography have different requirements. And this allows people who are more experienced in wildlife or portraits to write specific answers for those genres. Trying to lump everything together is I think the opposite of what we should be doing. If I search on Canon 70-200mm f/2.8 and see a number of questions about various genres, and comparing it to a variety of other lenses, I'd rather see all those questions and read through them, rather than have one general question which doesn't really address the specific angle I was after

Jeff again:

There are similar questions, yes, and so-called “exact” duplicates do happen, but they are kind of rare in my experience. It’s far more common to have many subtle variations of a question.

"Subtle variations" again. So are we sometimes being overzealous about closing questions? I think so. I think it discourages new people having their questions closed, and I think having a smaller set of questions discourages people from adding more answers if there are already 6 answers, one accepted. If a new question allowed, with a slightly different slant, it gives other people the chance to add their experience, where it is more relevant than on the more general "duplicate".

Questions where a poorly worded question already exists

Here we can edit the original question to make it better but I think we should simply allow a new, better question.

I think we should use a higher bar for determining a question is a duplicate. And I think if you find a related question, it's valuable to add that in a comment, but mark it as "related" rather than "possible duplicate".

Answer 1

Another case: confused questions which ask several different things at once, most or all of which are already answered.

Often this attracts replies which cover one aspect. Or, it attracts big omnibus answers which are hard to vote on (because they may cover one aspect better or worse). The end result is a Q/A which just clutters the site. Future visitors who wonder about some portion of the question end up with a lot to wade through. Basically this is the failure of bb-style discussion forums for Q&A, brought here.

I have been voting to close these as duplicates of the primary question and adding links to other questions. But I guess I could also be convinced that Not A Real Question, Too Localized, or Not Constructive would be better, maybe often with a suggestion that Chat is a good place to take a wide range of topics.

Answer 2

Let's take today's version of the lens question as an example, shall we? It boiled down to "I'm shooting things that move, and I'll be hand-holding, so is f/2.8 with IS better, or f/1.4 without?" Brand and focal length don't matter in the slightest, nor does the lensmaker's image stabilization efficiency. If f/2.8 can take the right picture at all, then f/1.4 is the wrong aperture; the lens's extra speed is moot. It's even less of a concern if you need to shoot at f/5.6 for adequate depth of field. And IS of any description won't make up for subject motion. All of this has been covered before (more than once), even if it didn't specifically mention Canon-brand 24mm lenses. And it really doesn't matter that the asker didn't want to hear any fundamental and inescapable truths.

At some point, we need to require people to make some inferences. What applies to lenses mounted on a Nikon often also apply to Canon, Pentax, Sony, Olympus and Hasselblad, for that matter. And yes, it is okay to edit both questions and answers to cover the general case when the specific is ridiculously specific (such as being brand-specific when the principles apply globally). There are already far too many "gear" questions on the site (probably because we're mostly tech-heads who've drifted in from other stacks and can't help ourselves), and I'd have no problem at all with a Great Purge (or at least a Great Merge). And maybe we can make the site about photography instead of about cameras.

Answer 3

I think that it's important to consider the generalized question when considering if something is a duplicate. Taking the typical Lens A vs Lens B scenario. Often it is something like Aperture vs IS in which case that is a general answer to a generalized question of IS vs Aperture and brand and even lens specific details don't matter if it is just that simple.

On a slightly more complex version of the same question however, there may be a reason why something specific to that particular lens or combination of lenses can't be quantified in a generally correct way. In this case, the question would not be a duplicate since the question can not be further generalized and thus a general answer is insufficient to answer it fully.

It's a tricky judgement call to make and I tend to avoid voting to close a question unless I know the answer well enough to be certain that it is in fact a duplicate. If not, we can always come back around to it after someone who does know the answer about the particular situation chimes in and if it is in fact generalizable, we can always close as duplicate at that point.

Perhaps the other thing we should try to do when we see this happening is to revisit the previous question and try to pull out the generalized question as opposed to an apparently equipment specific question that may be less obviously the answer. This would also (hopefully) reduce the number of duplicates asked in the first place.

Answer 4

I think there are three common cases of duplicates.

The first is the case where we already really do have awesome content on the question being asked. It's often the case that the new question is a straight-up duplicate, or even if the questions might not be identical, it's often the case that one of the other answers actually completely nails it. I don't think the automatic "possible duplicate" comment wording is as nice as it should be, but overall I think the process actually works pretty well here. We don't have a problem with moderators aggressively closing a question, so it actually takes a little bit of time, during which the question-asker can take a look at the information and see if it is helpful, and if not edit the question to better reflect the difference.

The second is basically "what focal length should I use..." lens recommendations. This maybe is a subset of the first, but here, we get the same question for different brands and even for different models, even though really the principles are the same. In this case, I feel pretty strongly that we're not really helping people by encouraging an illusion that there's a big brand difference in, for example, a cheap 50mm vs. the kit lens for baby photos.

And finally, there's the never ending stream of "Zoom lens A vs Zoom Lens B". Here, there really is a brand difference, and a price level difference, and a use-case difference. The worst case of these is when someone is in the grip of decision paralysis and has a list of half a dozen candidates with pros and cons for each and wants us to make a decision; these are probably best just closed as not constructive. But let's it's the more straightforward case of this 70-200mm vs that one. There are still a huge number of combinations, and I don't think exploring every possible permutation is really in the spirit of "multiple subtle variants" referred to above. That makes sense for people trying to understand crop factor, focal length, and sensor size; or even this recent think about how digital sensor ISO works. It makes even more sense when the question is about composition or style. For this, the Canon EF 70-200mm f/2.8L IS II USM is going to be the same no matter which other contender is in the list. So, I'd rather have one per-brand answer for different ranges of lenses where the answer is comprehensive. I tried to do that for Pentax primes at Which prime lens for Pentax APS-C?. This is a long answer, but it's not a case of "simple question (with a simple answer) where there is a more general question with longer, involved answers", because the A vs. B question isn't really "simple" — it's just phrased in an over-simplistic way.