StudentOfLight said:
Which legacy lenses are you hoping to resurrect and how good are they by today's standards? How would they hold up to the current crop of 24/36/42/50 MP sensors?
People around here keep asking that question (like its close relative, "will I have to replace my lenses if I buy a high MP camera?") as though no-one has used such lenses on modern dslrs or mirrorless cameras. But large numbers of people having been doing so for years, continue to do soon the latest cameras, and report the results on the internet in a wide range of blogs, forums, on flickr and elsewhere. The internet doesn't hide any of this, and you don't even have to venture far afield - check out Dustin Abbott's reviews of some very inexpensive ones, for instance.
If by "good ... by today's standards" you mean "would acquit themselves well in the labs of lenstip, photozone, lensrentals, etc." you might be surprised by how well many of them would do (even the hypercritical, Otus-loving Ming Thein's list of recommended gear includes a Zeiss CY prime and - gasp - a Zeiss CY zoom lens). But today's standards aren't the only ones that matter - one reason why some older lenses are popular is because they have an appealing but quite different look whose virtues result from "flaws" that prevent them from testing well (e.g. Photozone's clueless review of the Helios 40-2). Of course, there are also old lenses that won't seem very good (or worse) by any standard....
For my part, I own several current first rate (by current standards) lenses - including a few first rate Canon Ls, the outstanding Sony/Zeiss 35mm 2.8 & 55 1.8 primes and the astonishingly good Rokinon 135mm f2 - and a large number of legacy lenses made by a wide range of companies (many of which I hadn't even heard of a couple of years ago), including Canon, some of them ridiculously inexpensive. I use the latter group on my a7rII far more often than the former. (If I needed AF I wouldn't use them at all, of course.)
Some of this is a matter of taste, of course, and whether any of it applies to you depends on the sorts of photos you take....