That may sound stupid, but I would like to know whether lenses are sold with their back/front caps?
I plan to buy a new lens, and I would like to know.
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Sign up to join this communityEvery lens I have ever bought had front and back caps with it.
If you go to the manufacturer's website for the particular lens you are looking to buy, there is usually a "What's in the box" link, or a section in the specifications that lists the new-in-box package contents. Some manufacturers don't seem to list that information on their sites (for instance, I can't seem to find that information at Sigma's site), but reputable retailers usually list that information as well. For instance, B&H Photo/Video has a "What's in the box" section; Adorama lists the package contents, including front/rear caps, in the specs section for most of their products (at least for the several lenses I searched for).
Addendum (This is beyond the scope of the original question, but it is notable): An interesting distinction arose in the comments, that some kit bundles (such as the Sony a6000 w/ 16-50mm lens) don't come with a body cap or rear lens cap. My Nikon D800E w/ 28-300mm lens did come with both body cap and rear lens cap (and of course, front lens cap). According to the B&H "What's in the box" for the current Nikon D810 w/ 24-120mm lens kit lists a body cap but no rear cap (but then again, it doesn't list front lens cap, which I'm sure it comes with).
When it comes to body + lens kits, it's a mixed bag whether body cap and/or rear lens cap is included.
When buying new, yes.
When buying used, usually, but double check. It's uncommon for a lens to be sold without any caps at all, but not rare for the original ones to be substituted for generic replacements. These are usually (but not always) inferior. That doesn't affect your results, of course, but sometimes off-brand rear caps don't fit tightly and might fall off in your camera bag, and front caps sometimes have worse mechanisms for clipping into place.
Sometimes, the replacements are actually better. For example, Pentax Limited lenses come with these really nicely made metal screw-on caps, which are very fiddly and I was always worried that I might actually scratch the front element with the cap itself. A nice snap-on cap replaced that! (But the originals went into the box for possible future resale.)
Overall, when buying new, don't worry about it (but do complain if a "new" lens is missing lens caps!). When buying used, check — and maybe if they're significantly cheaper, factor that in to your price negotiations/considerations. (Replacement brand-name caps are often ridiculously priced.)