I'm just waiting for 5 butterfly images to be accepted, all of them taken with the Sigma 105mm. Some people are put off by the fact that you've got a smaller working distance but I like the challenge
Getting close to a timid butterfly with a 105mm isn't easy sometimes and it makes it feel a little more deserved than something taken with a telephoto. Many people here use the 150mm which gives a little more working distance, but still takes a little knowledge of your subject to use successfully
I'll add pics to the thread once accepted