What makes a lense "fast" ?

DavidEB wrote in post #2277249
a lens is fast if it goes home with you on the first date.

some people talk about lenses being "sharp" - that refers to lenses that look cool.

as the angryhampster said, "stick around, you'll learn new stuff every day." Or not.

Where's that thread with "definitions" of common photography terms? He should have a read with that.

I'm a reefer too. A tripod and lazy fish help for the reef pics. Reflections off the glass are bad with the flash. You probably want to the use AV mode and at first set the aperature as large as it will go. However I'm pretty sure that most lenses are also sharpest when not at their max aperature so If you can close the aperature (higher number) and still maintain shutter speed then do it. Also zooms lens are typically sharper in their mid ranges. That is... not zoomed all the way in OR zoomed all the way out.

An ideal lens for us reefers would be the 100mm 2.8 Macro (I don't have it)

In2Photos wrote in post #2276780
One thing you might want to consider is picking up the book Understanding Exposure by Bryan Peterson. It is regarded as the best book for learning the basics about photography. I picked up another book of his based on this book and find it invaluable.

@thefedz : I second the recommendation on the book. I have learned a ton from this book and it is something I still go back and reference.

Here's something else to consider. In photography and much like golf, better equipment (i.e., more expensive) brings better results. That said, even with the best golf equipment money can buy I doubt I'd be much of a threat to Tiger Woods with him using a set he picked up at a yard sale. The same idea holds true in photography. Better (faster, sharper, "L"s) equipment can certainly make up for some lack of skill, but doesn't make you an Ansel Adams either.

"Fast" nearly always refers to the aperture as already mentioned, but pay attention to context as "fast" can also refer to the AF of a lens as well. Without context assume it's a reference to the aperture. Your context was "crisp" which could be a function of both.

DavidEB wrote in post #2277249
a lens is fast if it goes home with you on the first date.

That sounds a bit one-sided and sexist, no ?
How about......a photographer is fast if she/he clicks that "order lens now" button before consulting its MTF graph?

no. that definition could apply to guys or gals.

Fast, by the way, is different from promiscuous. A photographer is promiscuous if he or she hops from one lens to another, without a commitment to any. If you're buying second hand lenses from such photographers, make sure they've been wearing filters.