Improper use of the lens refers to using the lens for its NOT INTENDED PURPOSE.Originally Posted by ST_sg
A prime lens has many uses, but zoom is obviously not one of them. At the point of taking a picture, you should ask yourself what your intended end is! If as B& S said, capturing images of your kids with some movement artifacts cause by a slower shutter speed is OK, then close down the lens, You get some more depth, but some movement which you may like. But if the background is distracting, the wide open aperture may be very good to reduce the distractions to a blur. So visualise the end results and chose the equipment and use its strength to your advantage.
I have L-lenses in zooms and primes. If I travel, I will bring my zooms. becasue it is often not possible to zoom with my legs. But I will always bring a 35 mm 1.4 for low light shots.
Dennis Kee mentions the 200/1.8. An absoluteley fabulous Canon lens together with two other similar lenses, from Leica and Zeiss. These are "no expenses spared in manufacturing" lenses. Marvellous! But I think shooting at 1.8 handholding at 1/250 is well, not recommended, putting it politely!
I would at least use a monopod if not a trupod for this. Too heavy, depth of foed too shallow. Room for error too high!