am new to photography and wanted a better lens for my XSI as the kit lens performance was no better than my Canon 35mm camera. I've spent a lot of time reading lens reviews and the choice has been the Cannon F1.8 for $100 or the F1.4 for $350. Finally I settled on the F1.8 and when I received it I took 8 or 10 pictures and they were just great, better than I expected. So of course I immediately ordered the F1.4 because I thought it had to be even better. A few days later I had both lenses in hand and took a bunch of photos with one and then the other and then compared them side by side on my big 24" computer monitor. I zoomed in and out and compared color, sharpness and bokeh ( Background blur).Many of the F1.8 lenses were sharper than the F1.4 lenses, but the F1.4 lenses were a little better in low light indoors and of course bokeh.I've come to the conclusion that the Overall image quality of the two lenses is about the same, but the F1.4 is much higher quality and the focus motor is much smoother and quieter than that of the F1.8 If you can afford the extra money, you should buy the F1.4 .However if you don't have that much to spend then you will be very happy with the F1.8.Or you can do what I did and take both.I have the F1.4 photo gallery two images of the same subject,same aperture etc added with the F1.8 and the F1.4 and I think you will agree that there is not much difference between the two lenses.