After saving up for quite a while to buy a decent tele zoom, all the while scouring reviews at the expense of getting enough sleep, I finally decided that the reviews I had been coming across for the Sigma 100-300 f4 were just too good to ignore. I was trying to avoid dropping $1K+ on a 100-400L, so based on the nearly universal stellar reviews for this lens, I bought one last week and it arrived last Saturday.
After trying to exercise SOME degree of discipline and finish the chores around the house I had started that morning (gotta keep the wife thinking the camera gear isn't more important to me than her honey-do list ), I unboxed the lens and matching 1.4x converter and hooked them up to my 50D for some tests.
The first lens I bought for this body was a good clean, used 55-250 IS that I got for $150. I discovered that little gem is a VERY good lens, despite how inexpensive it is. So that would be the "control" so to speak.
I went out in the back yard with some mixed shadows/sunlight under my trees, and started taking pictures of a cedar bird house I have mounted on a tree trunk about 35 feet away. This was a great test target, since it had really good detail in the aged cedar sides, and was sitting in a location and condition I'd expect to encounter when photographing wildlife outdoors.
Well, the only reason you spend money on a lens like this is to be able to get useable images wide open, right? Well, let's just say the shots at f4 stunk. They just stunk. No other way to put it. Softer than cotton, noticable CA, poor contrast, etc. I was shocked at how bad they were. I was expecting a LOT more.
After a bit, I had mounted the lens on a sturdy tripod, and took images at f4, f5.6, f8 and f11 of the birdhouse. I then took a few hand-held wide open at f5.6 with my 55-250 IS lens for comparison.
In short, the 55-250 kicked the Sigma's butt. I was having to stop that Sigma down to f8 to even compare to the cheap Canon, and even then the contrast wasn't as good. Plus, I was hand-holding the canon at 1/125, and the Sigma was on a tripod with a 2 sec. delay!
Well, after another day with basically the same results, I boxed up the lens and TC and returned them.
This was a lesson learned, but also the reason I bought from a reputable used camera store - because I knew they had a great return policy. Had I bought this lens on feebay, I'd be the proud new owner of a $600 boat anchor right now.
So, still saving. It looks like that 100-400L will be in my bag eventually anyway.
Just wanted to share that experience for anyone looking at reviews of that Sigma 100-300 f4 and thinking it can keep pace with top lenses for less. Unfortunately, at least the copy I had, could not.