Originally posted by jypfoto
Should I just suck it up and deal with the 24-70? Or should I consider the 28-75 swap, pick up a used 70-200 and/or pocket the savings?
You seem to consider acquiring other lenses as well (70-200), if so, the choice between 24-70 or 28-75 should not be done by considering one lens alone.
Case A) The DFA24-70 is the lens to have if you'll never buy a wide angle lens, because the DFA24-70 is sharp wide open at every focal length, you can use the 24mm for occasional wide angle shots., if wide angle is not your main interest and if you don't want to spend money on a UWA lens. Ultimately, you have two lenses: 24-70 + 70-200.
Case B) If you plan to do wide angle photography, then, 24mm isn't wide enough, so you'll buy a wide angle lens in addition to your standard zoom lens. In this case, your standard zoom lens FL may start at 28mm. If you plan to purchase a wide angle lens in the future, better get a cheaper standard zoom that starts at 28mm, such as the Tamron 28-75 or DFA28-105. Ultimately, you'll have three lenses: 1xUWA + 1x 28-75 (or 28-105) + 70-200.
Note that f2.8 isn't necessarily an advantage on a standard zoom like 24-70 or 28-75, because of what a standard zoom is meant to do, and the thinner DoF on FF. What I mean: with UWA, the hypoerfocal is fairly short so that you can have everything in focus even with f2.8 (f2.8 is useful for indoor architecture where you can't use multiple flashes). For a 70-200, the goal is to produce bokeh, hence f2.8 is an advantage. But for a standard zoom, you seldom shot at f2.8 because bokeh isn't best achieved with a standard zoom and more often than not, you want everything in focus.
I got the DFA24-70, but I use this lens with apertures between F5.6 and F22 in order to have everything in focus, so if I was to redo the purchase, I'd buy a DFA28-105 (silent AF, WR more versatile and half the price of the 24-70), and save the price difference to buy a UWA lens (already having the Tamy 70-200, works great on FF).
Hope this help.
---------- Post added 12-06-16 at 08:12 ----------
Originally posted by tromboads
28-75. Fits your bag. This is important And I doubt the 24-70 will be any sharper.
The 24-70 is definitely much sharper across the frame, wide open and stopped down. In the center, 24-70 is sharper wide open (if used wide open...). In the center and stopped down to f4, both are equally sharp.
---------- Post added 12-06-16 at 08:18 ----------
Originally posted by jypfoto
Is there any truth to the rumor that the 24-70 Pentax was put out as a holdover to a potential * version or a true Pentax design instead of a Tamron.
No way, the DFA24-70 (Tamron) rivals the best of Canon or Nikon, to the point that some Canon and Nikon users select the Tamron 24-70 for its sharpness, independent from the price. Yes, Ricoh sells the DFA24-70 at a premium , but not sure the lens would be better if they designed it themselves. Tamron and Sigma have recently upped their game, so that their new products rival or even beat the optical quality of OEM lenses (one of the reasons why Ricoh rebadged the Tamron 24-70).