what is the difference between Single lance (baby lance) 50mm 1.4f and 50mm 2.8f[picture quality]?

Answer 1

1.4 and 2.8...Hmmm One is half of the light gathering of the other..or put another way one has Double the light gathering ability of the other if the Objective lens is the same 50mm on both. Longer focal length lenses as a rule require more light or a wider aperture or f stop...they slow you down..which you compensate for by widening your aperture or f stop to allow more light to fall on to your film..Correct balance of shutter speed and aperture is crucial for good results with longer telephoto lenses.. With todays digital cameras..and even modern SLR program mode allows aperture priority or shutter priority which helps compensate for the light gathering deficiencies in longer telephoto equipment 150-300

Answer 2

Actually, an f/1.4 has four times the light-gathering capability of an f/2.8. The f/2.8 is good for low-light photography; the f/1.4, being two full stops lower, is good for really low-light photography.