I purchased this lens brand new to accompany my then new Canon EOS 5D around 18 months ago. I have to confess, I spent over two weeks prior to making my purchases deciding just which lens I should choose as my 'standard' zoom - this, or the also highly regarded Canon EF 24-70mm f/2.8 USM. In the end, I chose the 24-105 for reasons which I will divulge as we go along.

Next we move on to 50mm which we might normally consider to be that of a 'standard' prime lens on 35mm and full-frame digital cameras. And, so it is! With a viewpoint similar to that of the human eye - basically, what you see is what you get! If you wish to record things strictly as they are, then this is the ideal focal length. However, the same focal length can also be employed for slightly unusual and perhaps, more 'dynamic' close-up portraits. While we tend to consider short telephoto lenses 'most' suitable for such work, the 50mm focal length provides a somewhat more dynamic and 'involving' perspective when used close in. The shorter focal length and close proximity of the camera to the subject, produces slightly exaggerated perspective which, while not always desirable, can be used effectively for more involving and creative work.

For me, one of the great advantages to this lens over the 24-70mm, besides the fact that it is both lighter at 670g and more compact, is the incorporation of an excellent IS (Image Stabilisation) system. The 24-70mm lens does not have this facility and personally, I find the effective 3 f/stops IS to outweigh the 1 f/stop advantage at maximum aperture of the 24-70mm lens, permitting the use of shutter speeds up to three times slower than might otherwise have been expected to obtain still perfectly sharp results. Of course, it must be remembered that no image stabiliser can counteract subject movement, only that caused through camera shake.

Everything operates as should be expected for an 'L' series lens - very smoothly and precisely - with no sloppiness of slackness anywhere. The lens feels very substantial indeed and whilst relatively compact, does extend considerably when zooming towards the long end of the zoom range. In it's favour, the front element doesn't revolve either when zooming or focusing, so using polariser filters in no problem. With ring type USM (ultrasonic) AF, auto focus is both extremely fast and very quiet. FTM (full time manual) focusing is available, even when used in One Shot AF mode but is rarely needed due to the accuracy of the normal AF system.

To add to the slight disappointment, the lens also suffers from noticeable CA's (Chromatic Aberrations) or 'colour fringing', particularly at the 24mm end of the zoom. Whilst this is not a problem with all subjects, it can be annoying when dealing with high contrast ones or with some backlit subjects, especially trees or open building construction which might be set against a bright sky for example. Although CA's do decrease a little as you zoom in more closely, it is only beyond 50mm focal length when they become so low as to be of no concern. With the specification of this lens, I am however, a little surprised!