Originally posted by stevewong With the Longer lens may be easy than 100 mm
Actually it is harder, expecially if you are hand holding the lens. The FA*200mm f/4 ED and Sigma 180mm f/3.5 are hefty lenses* and the extra focal length frequently means you have to use higher shutter speeds to get usable images, but the practical upshot of the long focal length is that you don't have to be physically so close to your subjects to get close up images of them.
Pentax K5IIs with Sigma 180mm f/3.5 APO EX - Pentax AF160FC ringflash and supplemental lighting from wireless AF540 and AF360 + 82mm worth of extension tubes used
* some people complain that these two lenses are heavy, frankly I don't consider them to be prohibitively cumbersome. I'm no power lifter, but I find heavier lenses are easier to hold steady than light ones.