When a tripod is needed, a decent one is essential, and most high-end models don’t come with a bag. A good tripod is a long-term investment, so a decent bag is another essential, especially if you use it on location. Kevin Carter takes a closer look. I own both the Gitzo GC5101 and GC4101, which are designed for Gitzo’s Systematic range of tripods. While there’s only around 8cm or so in length between them, the GC5101 is much larger in terms of internal volume and was designed presumably for the Geant (Giant) model, a 5-series Systematic that still measures some 73cm (35-in) even when collapsed. I don’t have that tripod;…