I have 6 (yes, six) grandchildren who are growing up enjoying sports activities. My middle granddaughter is BIG into gymnastics. I have just learned that during competitions, flash CANNOT be used. So, I need my Nikonite friends to recommend an appropriate lens(es) for taking indoor shots at a distance. I will be using my D7100. Any other suggestions e.g. recommended ISO, etc. would also be appreciated. Thanks for taking the time to consider my post. 