Following are the comparisons between some of the well known lenses. Guess, which one is a better photograph in terms of sharpness, contrast and other parameters. As you scroll down the details of the lenses are mentioned. You will notice, that its not always the more expensive or a more hyped lens which gives a better image. And if it is difficult to make out the difference, then probably, it wont show anyways. However, the lenses compared here are all premium lenses, which would most of the times better than the cheaper ones. Depending upon the kind of photography you do, you may decide, if you really need to spend the money beyond a point. Lets, say for example if you do not need f 2.8, then f 4 will also give you the same quality and may be even better sometimes. Just compare !

It is generally known that a fixed or a prime lens is better than a zoom lens. Do you feel that same after going through the photographs above ?

Canon 50 mm f 1.4 is a much more expensive lens compared to the 40mm f 2.8 pan cake lens. If you do not really need the f 1.4, then 40 mm f 2.8 is not a bad lens at all. It is certainly better that than the 50 mm 1.8 version which has plastic mount compared to the 40mm which has a steel mount and a good construction.

The EF 70-300 gives you the additional 100mm which one misses out in the 70-200 mm lens. However, the maximum aperture is not f4 al through out the focal length range where as it is fixed in the 70-200. Go for the 70-300 if you need to reach out further for candid photography.  

Canon came out with the IS version of its macro lens with the same max aperture of f 2.8 Is it worth upgrading if you already have the older macro lens ? Only if you feel that Image stabilisation is going to help you with the hand held macro shots which you may be shooting.

Following are the images of the two popular versions of canon 70-200 mm lens

Following are the images from an expensive and a cheaper lens. which one is better ?

Four popular lenses of Canon compared together.

what happens when a cheap quality UV (ultra violet) filter is attached

Not difficult to guess that the image on the right is with a cheap uv filter where as the one on the left is without any filter. The lens is not an expensive lens. This clearly shows that saving a small amount of money on filter can have a huge impact on the image quality.