Non EF lenses on EOS cameras

I am sure there may be some threads on here about using non Canon Lenses on the EOS cameras but I am havign difficulty finding them with search so I figured i would ask.

With the abundance of older glass on places like ebay (specifically good 50mm and such) what are the pros and cons of using non canon glass with some sort of mount conversion?

The pros outweigh the cons by far - you can pick up some fantastic glass very cheap on ebay. The main loss is your maximum focus distance as you are adding a few mm between your camera and the lens so this affects the maximum focus. Closer up though they can be great and I have mounted a Pentax 50mm f/1.7 manual aperture lens on some of the cheapo ebay tubes to good effect in the past.
You'll also likely have no autofocus or aperture control, as I hinted to above, some lenses will have a manual aperture ring so you can set this manually although it does affect the brightness of the viewfinder the more you stop down.

https://photography-on-the.net/forum/showthre​ad.php?t=644277

https://photography-on-the.net/forum/showthre​ad.php?t=57023

Good breakdown here

Mike wrote in post #12649548
The pros outweigh the cons by far - you can pick up some fantastic glass very cheap on ebay. The main loss is your maximum focus distance as you are adding a few mm between your camera and the lens so this affects the maximum focus. Closer up though they can be great and I have mounted a Pentax 50mm f/1.7 manual aperture lens on some of the cheapo ebay tubes to good effect in the past.
You'll also likely have no autofocus or aperture control, as I hinted to above, some lenses will have a manual aperture ring so you can set this manually although it does affect the brightness of the viewfinder the more you stop down.

That's not really true. Most quality adapters are of the proper thickness to maintain the correct registration distance between the lens and sensor plane. Unless there is a mechanical interference of some sort (mirror hanging on rear element, etc) focusing to infinity is not a problem (this mainly applies to Canon's FF bodies such as the 5D and 5D2 and is not an issue with cropped sensor bodies). I shoot with many different manual focus lenses (Leica, Contax, Zeiss, Olympus, Mamiya, Pentax), and all focus to infinity just fine on my 5D2.

Mike wrote in post #12649548
The pros outweigh the cons by far

In quantity maybe, in weighting, maybe not.
True, you can find many cheap, good quality non-EF lenses, they have better build, and may be optically as good as the EF versions. However, for some, using MF only is a huge drawback. I find it extremely difficult to manually focus with a fast lens on my 450D, so I'd never again give up AF to save money.

Thats only true if all different SLR systems out there have the same flange focal distance as the current Canon system.