Brief History of the Single Lens Reflex Camera
This article will be the first of several that explain equipment! These aren't intended to be gear-lust-inducing, but mostly informative.
To start this series off, we'll go over what is the most common kind of camera: the single lens reflex or SLR. I'll mostly be doing a summary/write up of a few different sources, which I'll link at the end.
Single Lens Reflex basically describes how the light travels during use of the camera. Here, there's one lens that allows the photographer to observe the scene and that same lens is then used to make the exposure.
This sounds pretty common sense, but you'd be surprised at how much technological advancement had to happen before the SLR could be developed!
The first commercially useful photographs were actually Daguerrotypes and used a huge camera with light-sensitive glass plates…in 1839. These were large, boxy cameras that recorded positives and were inverted; meaning that the images couldn't be enlarged and they were technically exposed upside down and with left and right flipped! While this inversion didn't matter as much for the final image, it made using the camera very tricky.
The addition of the mirror in the light path (reflex) meant that at least one axis was no longer inverted and this drastically simplified operation. To give a point of comparison, I have a twin-lens reflex (TLR) camera which has only one inverted axes and every time I use my TLR, I have to retrain myself on how to aim. I'll write up an article on TLRs later, don't worry =)
The first commercially produced single lens reflex cameras were the Monocular Duplexes made in 1884 by Calvin Rae Smith. These still used ground glass for viewing on a waist-level finder (we'll get to that in another article, haha) and a hood to keep out extra light and had each of the mechanisms as separate (raise mirror, open shutter, close shutter, lower mirror).
Eventually, these technologies would be shrunk and incorporated into other format sizes! You can find SLRs in half frame 35mm (http://macfilos.com/photo/2016/6/14/olympus-pen-ft-mju1-film-cameras-vintage-films-not-dead, https://www.imagingpixel.com/p/olympus-pen-ft-half-frame-slr.html); medium format in 6 cm x 4.5 cm, 6 cm x 6 cm, and 6 cm x 7 cm (https://www.thephoblographer.com/2015/04/25/the-four-best-medium-format-slr-cameras-you-can-get/); and of course "full frame" 35mm which would in turn dominate the market... Until digital.
A lot of people still distinguish between SLR and digital SLRs (dSLR), but to be honest, I don't see the point of doing that. The light path goes in the same direction and film SLRs are so rare now (as of this draft, both Canon and Nikon have discontinued their high end film SLRs) that most SLRs in use are digital.
I consider SLR to be the "workhorse" style of camera. They're generally useful and can be adapted to whatever use case is needed, but are also a bit of "jack of all trades, master of none". For example, you can find smaller and more discreet cameras for street photography, and you can find larger cameras for more detail and enlargement capability for landscapes and still life, but an SLR with good lenses will get most things done well enough.
Now it's impossible for me to have used all equipment, but I do have my favorite SLRs.
Size: I'm a big fan of the Olympus OM system for its small size, beautiful viewfinders, and excellent ergonomics! If you're looking for a stylish looking camera that's easy to pack (and you can meter yourself), it's hard to knock the OM-1 with the kit 50mm 1.8.
Main: My main SLRs are the Canon EOS system. Durable workhorses with lots of lens selection and relatively easy to get serviced. Also, they have one of my favorite lenses (the 100mm f2.8 L Macro IS).
Current favorite: I love the digital Pentax cameras. Menus are fast, buttons and controls make sense, and there's not much of a learning curve when moving between different bodies; the menus and button layout between the K-3 was very similar to the 645D and 645Z
I also do have a wishlist! I briefly used a Rollei 6008 (see the nice pictures here http://forum.xitek.com/thread-866921-1-1-1.html) and I loved the lenses and medium format negative…but the camera itself was finicky due to odd electronics. If I ever found a reasonably priced one of those that worked…or the Hasselblad… (https://www.imaging-resource.com/news/2013/04/29/end-of-an-era-hasselblad-v-system-takes-its-final-bow) I'd also love to try some of the Contax SLRs as I've heard good things about their Zeiss lenses (http://camerapedia.wikia.com/wiki/Contax_RTS_III).