Cheap lenses have their places, especially in the old days when good lenses are very expensive. Inexpensive lenses enabled those who want to get into photography, but not willing to spend the money to buy a good, but expensive lens. In film days, most cheap lenses actually produced pretty acceptable results, because most people only print 4x6 size pictures. At that size, even a coke bottle at f8 could make passable pictures.
I have MANY cheap lenses. Some are better than others, but in general, you get what you paid for. Take for example, the Hanimex 200mm f3.3, which I bought for around $15. This M42 lens looks quite impressive with its 67mm filter size and multi-layer coating. Tried it today on the 5D, and the result is as expected -- I got $15's worth of optical quality from a $15 lens. The lens is soft wide open, has green colour fringing, and needs to stop down to f8 for acceptably sharp pictures. Oh, the colour is totally unexciting. You may say it can be changed with post processing, but if it's not there in the first place, it ain't gonna look good no matter how you massage it.
There is one good thing about the lens. It's acutally quite well built.
So, the saying "You get what you paid for" is certainly true in this case.
Yum -- 5D & Hanimex 200mm f3.3. Larger Picture.
Stopping at the red light -- 5D & Hanimex 200mm f3.3. Larger Picture.
Conversation -- 5D & Hanimex 200mm f3.3. Larger Picture.