A camera shop recently told me my sigma 18-50/17-70 f2.8-4 (I run 2 mounts and have one on each camera) should be replaced with a constant f4 lens. This conversation came about when they tried to sell me f2.8 and I wasn't interested due to weight and cost, and more importantly having 0 issues with what I'm running. They insisted the f4 would be better quality no matter what and bokeh would be better. That argument makes no sense to me, is there any truth in it? I'm sure some constant f4 lenses will be optically amazing, but are variables really that bad? Don't think the shop understood I just wanted a tripod, ended up not getting anything at all.