Don't be afraid to Experiment with Hi ISO's
Many photographers have historically be reluctant to photograph their subjects at high ISO's. The reason of course is that the subject would often develop a sandy or grainy appearance. While this may appeal to some who photograph in black and white with an artistic flair, it is typically not very complimentary to those who photograph glamour images.
Even so, modern cameras made within the last 5 years handle noise rather well. Full format cameras tend to do a little better than cropped sensor camera, but surprisingly enough even some camera phones do pretty well in low light conditions. The exposure triage (ISO, aperture, shutter speed) are all intimately related. Typically, when you raise or lower one of these elements, it affects the others unless you are in full manual mode. In the image above, I was in an aquarium in a section with tropical fish. For those who have visited aquariums, lighting is often very subdued not only in the walkway, but at times even in the tanks.
I wanted to get a few shots of the fish, but there were some obstacles that needed to be considered. Fish, typically will not stop and pose for a quick pic, and even if they are still for a second or two their fins are still moving. Obviously the fish were in a glass tank, so flash was out of the question in this case. The fish were moving toward and away from the glass at a fairly brisk pace at times so there was only a very slim window of opportunity for a good image.
During this day I was shooting with my 50 mm 1.8 lens. This is certainly not one of the high end sports lenses, but I thought I would give it a try. After a few trial shots, I ended up with a shutter speed to 1/40 sec, f 5, and an ISO of 25,600! While not tack sharp, it certainly got me the image that I wanted for several of the sealife during the day.
Photographers sometimes get comfortable shooting with certain settings most of the time. Of course, when shooting for a client one wants the best possible images. Every now and again, we may be surprised by trying something new and stretching the limits of what our cameras are truly capable of producing!