gonzogolf wrote in post #16445915
Think of it this way. At 1.2 at 8 feet from the subject your DOF is a tad over 2 inches total. At F4 same distance its over 6 inches. So you have little latitude to miss focus a bit when you arent shooting wide open. People were using that lens long before micro adjust existed so its not necessary, but is probably most helpful when you are shooting wide open.
Thanks!
EverydayGetaway wrote in post #16445932
I would just use your Tamron 70-300. I would think it'd make a decent family portrait lens. If not, check out the 85/1.8 or Samyang 85mm.
I could use it, but since I'm not charging for the session and they're going to pay for a lens, I figured I'd take the change to play with a new toy. 
facedodge wrote in post #16445936
I like the 135L for family photos. Usually f/2.8 is deep enough for all faces to be in focus so long as you are far enough away to get the whole body in the shot like this...
Large version
here
I stop down to f/3.5 to f/4 if I get closer like this. I was losing light so I was trying to be as fast as possible.
Large version
here
I did a senior shoot a few weeks ago (my first ever shoot and what spawned my up coming one) with the the 135L. Fantastic lens. Just figured I'd take this chance to try out a different lens to see how I liked it.
xarqi wrote in post #16445961
There's no doubt that the 85L is a terrific lens, but I don't think it would be my first choice for family portraits, especially since you would be unlikely to want its main feature, its very wide aperture. The reason is that for groups, and family portraits, a very shallow depth of field is rarely desirable. If you are going to be shooting at f/5.6 or thereabouts, the 85/1.8 would do just as well at less cost, indeed your Tamron zoom would fill the bill.
The second aspect is that 85 mm may prove a little long for groups unless you have quite a lot of space in which to work.
My suggestion would be that you rent the 24-70/2.8L instead. In addition, give careful consideration to lighting, as this is key to the achievement of optimal portraits (and indeed any photograph).
Thanks, I never thought about going with the 24-70. I guess I had slight tunnel vision on that 85. My Tamron would do fine, I agree. I just wanted to take this chance to play around with a new toy. 
I've actually been contemplating purchasing the 85 f/1.8 or the 100 f/2 but I've went back and forth because of the purple fringing that you always hear about.