Getting into photography as a hobby need not be expensive. But charging clients for photography implies an obligation to deliver polished results. This means not skimping on the gear.
A professional photographer has backups of every piece of gear. The backup isn't necessarily identical to the primary gear, but it does have to be good enough to meet the requirements of the event.
Typically the gear list might include:
- main camera body -- and this is probably a professional grade camera body (not an entry level body nor a mid-level body) and it probably costs in excess of $2500 for the body only.
- backup camera body -- this might be the camera body that used to be the 'primary' body before the photographer upgraded the camera, but it probably at least qualifies as a mid-level body (not an entry body) but current standards. In other words it's probably roughly a $1200-1700 body. e.g. if a photographer's primary body is a Canon 5D III then maybe the backup body is a 5D II (even though that body isn't still made -- it's close in performance to a 6D, but with a better build quality than a 6D).
- lenses... and there are two that every professional wedding photographer owns
1) A 24-70mm f/2.8 zoom (expect to spend $2k or more)
2) A 70-200mm f/2.8 zoom (expect to spend $1800 or more)
Those are sometimes called the "bread & butter" lenses -- they are the most popular lenses in use by pros.
There are also a number of other lenses that a wedding photographer *might* have such as an 85mm prime, maybe even a 50mm prime. Some photographers will have an ultra-wide zoom such as a 12-24mm. (expect to spend $1200, but Canon's new 11-24mm is $3k)
These are not cheap lenses. The thing is, these are very high quality lenses with low focal ratios, usually very fast and responsive focus motors, well-rounded apertures, and optics that do a good job of controlling unwanted optical issues such as flare, CA, distortion, etc. and yes... it does make a noticeable difference in the product you can deliver.
And then there's the lighting... typically a couple of high-end strobes and triggers for off-camera use. Light modifiers such as soft-boxes, reflectors, perhaps umbrellas, grids, etc.
This is not a complete list (there are lots of other things such as tripods, light stands, a gray card, flash brackets, etc.)
The computer MUST use a color-calibrated monitor and that means buying a monitor calibration device such as an X-Rite Colormunki or a Datacolor Spyder.
BTW, megapixels only need be high enough to produce quality results... once that's attained, having "more" megapixels is not necessarily what the photographer is after. ISO performance and dynamic range are often better with lower density sensors. The 50MP Canon 5Ds is not intended a wedding event camera.
Anyway, you asked... so there's the list. You can see it's not a cheap list. It's easily $10k worth of equipment.
But far more important than the gear is the knowledge to use it that takes study and practice. I am fond of pointing out that if I go buy a concert grand piano it will not transform me into a concert pianist -- that's a skill I have to learn on my own.
With that study and practice usually comes some realization of what you can and can't do with a given piece of gear... and an understanding of why having some specific piece of gear would be advantageous to the situation.
I must gently point out that if you sensed a certain tone with some of the replies in this thread, the reason for it may be that if someone has invested the time to develop their skills to the point that they're ready to go shoot weddings, then they would have almost certainly learned what sort of gear would likely be necessary and would not be asking such a broad or generic question (they might ask a question which is a bit more specific... such as the difference between two products. e.g. is the $1300 Sigma 70-200 f/2.8 is as good as the Nikon 70-200mm f/2.8.)
Both Canon and Nikon have somewhere in the neighborhood of 75 lenses available for their camera systems. Each lens is still marketed for a reason. Some of that gear is designed to be less expensive and more attractive to entry-level customers. Some of that gear is designed to meet the demanding needs of professional photographers. Trust me when I say that if a professional though they could get the same quality out of an entry-level 55-250mm zoom that retails for $299 that they can get from a professional grade 70-200mm lens that retails for $2200... they'd go for that $299 lens. There's a reason the pro spends the money high end lens.
If you do a portrait shoot and the images don't turn out then it's possible that you might be able to re-shoot the portraits at a later date. But if you shoot a wedding and the pictures don't turn out... you've just ruined someone's wedding photos. Naturally the pressure is a bit higher for the wedding photographer.