« on: October 23, 2013, 01:28:38 AM »
I would concur with the 85 f1.8 for crop or FF. My favorite portrait lens is the 70-200 on crop or FF, so I would agree that the focal length would work well.
For shorter lenses, I have the old non-IS 35 f2.0. It is a good lens and relatively sharp on crop. For closer portrait/candids, the isolation has been quite pleasing. But, I have essentially replaced this lens with the 40 f2.8 pancake on either crop of FF for those times when I don't want the bigger zoom.
One other note. For infants, I would recommend a USM or STM lens. When my daughter was young, my old Tokina 28-200 (on a film Rebel) was so loud in focusing that it often spoiled the moment because my daughter would hear it. I switched to a short Canon USM zoom and had better success at these moments. Maybe this won't be a big issue, but the 50 1.8 and the older 35 2.0 just might be loud enough to spoil some moments, especially at close range.
All things considered, I'd grab the 85 f1.8. Even on crop, I think it will give you enough room to frame portraits in most indoor settings. It will also give you the isolation that you're looking for and would be great "stealth" lens for candids. I love my 70-200 f2.8, but the 85 f1.8 and the very similar 100 f2.0 are still on my wish list for this reason.
Frankly, if people, candids, and portraits are the norm, then the 40 f2.8 and the 85 f1.8 would make a nice combination.