I often hear, "Only pick a certain wedding photographer because he or she uses a particular brand of camera/lens, usually Nikon or Canon." I used to use Canon exclusively until I was struggling with the weight due to a) getting older and b) carrying a shoulder and knee injury from my Policing days - yes, I was one of North Wales' finest for 32 years, retiring in 2008, when I took up Wedding Photography professionally.
In March 2014, I was introduced to the Olympus OM-D-EM micro four thirds camera system, smaller and lighter than my Canon kit but with equally good image quality if using their higher grade lenses. According to Olympus, the EM1 model at the time was designed to out perform the DSLR and is splashproof, dust proof but unlike the Canon system I was using, freeze proof down to minus 10!
I dipped my toe into the system but kept my Canon kit at the same time. However, in November 2016, I finally took the plunge and now exclusively use an Olympus OM-D-EM1 with a 12-100 (24-200 equivalent) Pro lens (the focal length on the M4/3rd system is double so you get smaller lenses but longer focal length- perfect for candid shots at weddings.) As a second camera, I use a Panasonic Lumix GX80 - also M4/3rds so the Olympus and Panasonic lenses are interchangeable with both cameras as the system was designed jointly by Olympus and Panasonic.
For weddings, I use a 25mm lens on the Lumix which gives me a 50mm equivalent, ideal for head and shoulder portraits and I get excellent bokeh (out of focus background), making the subject pop out when using the narrow depth of field this lens gives me. I also have two Lumix lenses which I keep in my bag in the unlikely event of equipment failure.
More and more wedding photographers are turning to the M4/3rd system along with other mirrorless brands such as Fuji and Sony so don't be put off by photographers using these systems as they are as good at producing quality images as the one's using the likes of Nikon or Canon.
Another plus for me on the weight side was after a long day shooting with my Canon kit, I would be full of aches and pains the next day. Now, I don't have problems of that nature after a wedding shoot.