Difference between still and video lenses?
 

I apologize in advance if this has been covered, but should lens selection be based on whether one is shooting stills or video, or can the same set of lenses work equally for both? Thanks!

From my perspective, since there is no flashlight in video, the speed of the lens is probably more important than the absolute sharpness as all lenses are trade-offs of various features. The second thing I think its important is the focus ring--whether it is smooth or rotates in the direction you want. You probably don't want to have a set of lenses that have different focus ring directions.

Yes the same set of lenses can be used for still or video.

Any stills lens is going to be a compromise for video because that is not what it was primarily designed for.

Having said that, some lenses are (by chance/luck/design) better for video than other still lenses. Here's a few important considerations:

1) Constant aperture - some zoom lenses have the same maximum aperture no matter what the focal length, whereas others will have a smaller maximum aperture at full zoom. Constant aperture lenses let you zoom in/out without having to adjust exposure mid shot which can be very obvious on DSLR's which aren't designed with the same stepless smooth adjustments as most camcorders.

2) Focus ring - some lenses are designed entirely for autofocus and have terrible focus rings which are difficult to grip or rotate. I've even seen some cheaper Canon lenses that don't have a focus ring at all. Obviously this will be a problem for video because you need manual focus.

3) Parfocal/varifocal - most camcorder lenses are parfocal, meaning that focus distance stays the same regardless of zoom. This allows you to zoom in fully, focus, then zoom and to frame your shot, knowing you can zoom in or out at any time without ruining your perfect focus. Most still zoom lenses are varifocal, meaning that when the zoom changes, so too does the focus distance. So zooming midway through a shot becomes very difficult or impossible.

In reality I do not zoom in or out with a dslr while shooting video, that is a camcorder shot. I have some parfocal zooms, but I don't need to zoom in to focus then zoom out to frame the shot, as my Canon 7D has a x5 and x10 magnifier of the rear LCD image that does that for me, or use an external monitor like Marshall that has focus assist.