I was looking at some family pictures I have taken with both my HD Pentax-D FA 28-105mm F3.5-5.6 (to give it, almost it's full name) and my D FA 100 Macro F 2.8...attached to my K1 over the past year or so.
With family pix, I generally take these inside , in available light. I just up my ISO, use aperture priority, focus on the subject's eye and generally tend to stay around the F 2.8 to F 5.6 settings.
Now, we have some speed 'merchants' in our family, two...namely our little grandson and our daughter's big husky/greyhound. Both move around quickly without letup, it seems, and won't sit still and say cheese, like everybody else.
So in order to get pix of them, I also try to ensure, I have half decent shutter speed too...nothing incredibly fast, but enough to work with.
Anyways with the 28-105 I find I'm mostly using F 3.5 to around F 4...in interior, natural light shots. Of course the upped ISO makes a significant difference and the K1 I find has pretty good resolution to my eye @ 3200-6400 ISO...so even with the 28-105 which isn't a phenomenally fast lens... the picture quality is still quite good, if I don't say so myself,
, thanks to technology...ie; high ISO performance.
Yep, I admit, sometimes I wonder what would that Canon 85mm F 1.2 be like to work with, but on the other hand @ $ 1850 CAD for this lens alone, that's not within my budget. But I'm not wistful for that fast Canon F 1.2 , as my relatively slow 28-105 and 100 F 2.8 Macro really do the job. For me.