Do you REALLY see image quality issues by having that lens in place?
Yes, I definitely see image quality issues. Whether that is their cause is unclear.
It's very difficult to compare without images of the exact same subjects with both an adapted and equivalent non adapted lens. But chromatic aberration is extremely noticeable, almost rampant right off the bat in all of those images (to the point where in some cases, blades of grass are completely separated into two images in different wavelengths that don't even touch one another). And there is ghosting in a couple of them, and the colors seem fairly off in a few (possibly also CA, or possibly due to attempts to fix other things like low contrast).
Impossible to say which if any of those things might be due to the adapter, but as standalone images they most certainly do
not scream "holy **** these are optically perfect, so there must be nothing wrong with the adapter." There are quite visible optical imperfections in them without having to squint your eyes at all, and it very well MIGHT be due to that adaptation.
That said, the amount of optical flaws there, even if we assume they are all due to the adapter, may very well be justified by the cheaper cost, depending on just how budget-minded one is. It's not like you duct taped a magnifying glass onto a Holga or anything.
Because I have you on ignore, as I explained to you via PM when I put you there, I didn't see this until just now.
None of what you describe is due to the adapter lens. If you see things you don't like, it's due to my overzealous editing, especially the cranking of the saturation, which tends to bring out the magenta in some brown hues.
As an example, here's a straight RAW to JPG of one that probably has most of what you describe as "image quality issues" while you inferred they are likely caused by the adapter, while covering your butt by saying it's hard to tell:
There's nothing going on here but a re-size in the conversion to JPG. I didn't even bother to brighten it up or give it basic sharpening, and certainly no CA correction - nothing.
Now I'll do the basics: Brighten with exposure adjustment, contrast and sharpen, but still NO CA CORRECTION:
Now point out where, "chromatic aberration is extremely noticeable, almost rampant right off the bat in all of those images (to the point where in some cases, blades of grass are completely separated into two images in different wavelengths that don't even touch one another)". By the way, I'm not a noob. If there were
actual CA involved, I'd have just filtered it out in post, the way I do for any lens that produces it, and that's the case for lenses that have nothing to do with an adapter, btw. It's simply not necessary to take that step with this lens and adapter, and cranking the CA sliders in post had no effect at all, just F.Y.I.
So yes, you're correct, it
IS hard to tell if an adapter produces quality issues - when you have no experience to actually base it on, which, as usual, you don't. (Even though I have you on ignore, people quote you, so I see enough to remember why I put you on ignore in the first place)
So here's an idea for you to try for a change: Before you deem yourself "professor" on every subject that comes and goes around here, even going so far as to dig up long-dead threads to start arguing about them; Before you decide to jump in with both feet to educate others about techniques or gear, get some ACTUAL hands-on experience with the techniques or gear in question first, and then speak from actual knowledge on the subjects.
This is actual experience talking: FD to EF adapters actually work really well, especially for the cost savings if you already have FD lenses to use and are on a tight budget.
Yes, they require manual focus and aperture adjustments. If that's too much for someone to handle, I suggest they don't use them, and would further suggest they think twice about using the term "photographer" to describe themselves. Then again, I come from a time when there was no "auto" associated with focus, aperture or ASA/ISO, so it's not a big deal to me. Crazy as it may be, I still occasionally shoot some of my old film cameras where all that manual focus and aperture stuff is still required because they have no "auto" anything - many don't even have a built in meter and don't use batteries of any kind (GASP!!!)
Don't get me wrong, I love modern digital cameras and AF and choosing aperture, shutter and ISO on the fly electronically, but I don't cry when it's not available for some reason, like if I'm using adapters or bellows or cheaper extension tubes or reversed or stacked lenses or older film cameras. I guess you could say I'm the kind of guy that can actually get up from the couch and change the TV station if I don't happen to know where the remote is.
Now then, since you will no doubt use this post as a launchpad to try to argue about it (it's okay - you obviously can't help yourself), just know that I have no interest in that, nor in anything you have to say frankly, so you won't get an answer from me when you do. I only answered this one because I thought it would be fair to everyone else for them to see the actual unedited image for themselves, rather than leave your uninformed post as the definitive last word on it to negatively influence those who might tune in to this thread in the future.