Not quite true… Zeiss still have very good optics - as found on Sony cameras - and a few others, I think.
The Contax (which Zeiss owned) name was ‘revived’ by Zeiss, working with Yashica, via the Contax RTS, in 1975. Yashica were later bought by Kyocera, who continued with the Contax line until 2005.
[I have owned a number of Contax SLR’s (139, 137MA & 167MT) and a few Zeiss lenses (50/1.7, 28/2.8, 35, 2.8, 25/2.8). I defected to Nikon, when I went Digital…]
Thanks…
It was the Kyocera buy out that I was think of then, rather than the Yashica connection. That makes more sense now.
The Duoflex actuated the mirror in response to pressing the shutter button and the mirror dropped down when the shutter button was released. The Pentax was the first to automate this process by spring loading the mirror for return instantly the shutter had fired.
As for the pentaprism it was actually invented by Staudinger in Germany in the 1930’s, nobody wanted to manufacture it but there seems to be some debate over who pioneered the pentaprism finder but the sources I have seen talk about Rectaflex beating Contax to market with the first by a year. It was Pentax though who put together the pentaprism and the instant return mirror for the first time in a single camera - the Asahi Pentax of 1957. Those same sources also indicate that Pentax adopted the film advance lever (pioneered by Leica M3 of 1953). Bringing all three technologies together means Pentax effectively invented the single lens reflex as we know it today.
Contax - now there’s a maker of gorgeous cameras!! I recall how much I drooled over their 139 with its leather clad body and Carl Zeiss lenses in my teen years… Interestingly both Contax and Pentax worked with Philips to pioneer the world’s first full frame DSLR but Pentax were unhappy with the quality of the Philips sensor and pulled the plug after building their MZ-D prototype. Contax pressed on and launched the N Digital before Nikon or Canon had a full frame DSLR on the market. In truth though they sadly were pushing the tech envelope too hard and the camera did not sell well.
Pentax also invented the first 35mm autofocus SLR (The Pentax ME-F) but it too came too early (1981) and didn’t really take off and it was Minolta with their Dynax 7000 of 1985 that really hit a home run.
Similarly Pentax also pioneered mirrorless interchangeable lens photography with the Pentax KO1 which was backwards compatible with all K bayonet mount cameras but that too failed to capture the zeitgeist.
It seems in photography that being first or being most innovative isn’t always the way to achieve market leadership!
I think the Wikipedia SLR history is a good read and seems pretty accurate: History of the single-lens reflex camera - Wikipedia
Jonathan
Rangefinders weren’t totally killed off my SLRs and remain as the favoured choice for many photographers and I expect the same will happen with dSLRs, a much loved and wanted niche product. Digital was going to kill off film. Film is still going strong for a largish number of photographers. Phone cameras were going to kill of cameras, sure they have destroyed the cheap point-and-shoot market but a fair few younger photographers started with their phone and have moved on to a dedicated camera of some kind.
Thinking about hi-fi, I remember CDs were going to kill of LPs, they didn’t. Streaming or downloading was going to kill of CDs, they are still being made and sold.
@JonathanG - Thank you for that illuminating post.
Hope people don’t file in under TL;DR though… 
From what little I have read, the key ‘names’ seem to have been Zeiss (as Contax) and Pentax. But what they both did was to pull together ideas what other much lesser known companies had introduced earlier.
Yes, Wikipedia - History of the SLR
I will admit that I not only drooled over the Contax 139 - I bought & used one, as my only camera, for over 10 years. I could not really afford the Zeiss lenses, though - but the 28/2.8 I did get was fabulous…!!
True, Pentax put together a number of innovations (including some patented by other manufacturers!) to form the basis of what became the ‘standard’ format for SLR cameras.
That may have come across as rather disparaging…
Putting al those pieces together that way was itself a very significant innovation.
Ian, you’re a lucky man with that 139!! I still do drool over Contax and Zeiss - just the most beautifully made cameras. As you say I bet it was a struggle to afford the Zeiss glass - but oh so sumptuous when you did!
It’s interesting isn’t it how so much of the joy of photography is down to the handling and design and appreciation of beautifully made cameras and lenses. I think Leica really understand this and have made a success of marketing to a customer base who feel this way. Contax totally understood it too and their SLR’s and rangefinders are glorious to this day. Pentax I think are seeking to move in the same sort of direction with their focus on building beautiful handling bodies and mating them to fabulously made primes like the Pentax Limited 31mm, 43mm, 77mm or fabulously made zooms like the 20-40mm etc. PENTAX Limited Lens Special Site | RICOH IMAGING
It’s always struck me as a shame that nobody ever resurrected Contax - Fuji have made such a success of copying their sixties rangefinder styles I’d have paid good money to have had them even better built and with a Contax badge and Zeiss lens on the front!
Jonathan
I did not say the the Nikon F was the first System Camera…
(NB. I have deleted my previous post.)
That is more the debate of film vs digital cameras, rather than optical vs electronic viewfinders, and I think also you’re including auto exposure, aperture and focus vs manual in there too, which are irrelevant to the electronic viewfinder vs pentaprism optical. Meanwhile if the scene is so dark as to have very little visible in the viewfinder (or if using infrared), it would be hard to instinctively get the exposure right, as you put it. Of course you can take a photo, multiple and sufficiently wide bracketing, hoping one is right - if a potentially changing subject then I’d prefer to be shooting multiple photos with the right exposure in the same time (and still bracket if an image that can’t be recaptured)
I used to have a 139 back in the early 80s, unfortunately, it got stolen.
I recently bought a Canon Eos R6 to replace an Eos R. I was never happy with the R, always felt ‘clunky’ and slow and I felt the images were a little noisy. The R6 is a different beast altogether, super fast, really low noise and the focus system is incredibly good. It’s the first mirrorless camera I’ve used that handles like a proper camera. I won’t be using a traditional dslr again
I traded in my 139 - and 137 - to buy my 167MT - when Jessops still had proper shops… 
I also acquired some Zeiss MM lenses, to match the 167. Definitely a blind alley… lols.
For some people, just like hifi for some people. We are all different: I get joy pf photography in taking the picture, with as little fuss as possible (which doesn’t mean auto everything) and subsequently viewing that perfect (!!) image. For me the important thing with the gear is optical and capturing quality, followed by ease of use, and nothing to do with the appearance or feel - rather like hifi for me! My brother in law who has turned his hobby into his business gets most joy from taking the picture, where he will spend hours getting it just how he wants, and from ownership of a good gear - and for him tge feel is important, preferring the weight of his Canon 1DS bodies to anything lightweight like the latest mirrorless - though when he tried my R he was surprised, and I would’t be surprised if he buys himself an R5 before long…
I don’t really see that there is an analogue or digital debate anymore - both are used - and I use both - but admittedly not very often film now. I say film is basically an artisan/specialist medium now.
Not so much with with colour which I have processed at a lab, but B/W I can push and pull negative developing to get an effect… yes you can achieve almost the same with a digital work station - but its not as ‘fun’ and misses that slightly imperfect look you can get with film.
I think with photography one needs to think about not letting the camera and lens becoming a barrier to making or capturing the image… and that is why I embrace smaller bodies and small quality lens, good balance and ergonomics and robustness … and ultimately depending on the image - size and convenience and imaging flexibility can be more important that total quality. I still have my 645 Bronica - but rarely used now - although it is probably still my goto black and white film camera - and have a few of its images up around the office here,
I guess if a DSLR became available and offered the same picture creating capabilities as a mirrorless - ie in a small full frame camera, fast small lens lenses and low light stabilisation then it would be equally great. Mirrorless allows that - it’s just a more convenient tool for me - but the fact of a camera being mirrorless is kind of irrelevant - it’s the benefits and outcomes it achieves. My current Nikon Z72 with Z14-24 F2.8 S or Z24-70 F2.8 S fits within the length of my hand, and is a joy to work with - my Z24-70 F4 S is significantly smaller and lighter still.
I maintain cameras are ultimately changeable - it’s the lenses one invests in for long periods of time until they just wear out… such as my beloved AFS 17-35 F2.8D lens which has been a great film, and digital SLR lens as well as mirrorless - but after many thousands of images later, a full service by Nikon UK, and some abuse out in the field over the years, the mechanism is just starting to get a little tired now, but optically still great.
I remember watching a TV series about serious photography quite a few years back. Digital had arrived, but was not taken all that seriously then. The person presenting the programme showed a black and white photo which was basically someone walking alongside a very long low building, past a doorway or similar.
He said “I think this photo was taken on a digital camera because the figure has walked a foot or two past the point of perfect composition.” “With a film camera, the photographer would have been able to catch the figure at exactly the right moment. But he didn’t allow for the extra delay in a digital camera.” And then they did a sort of edit that put the issue right and it’s true the composition sort of clicked into place.
Of course things are different now and have been for a long time. But it was still an effective lesson at the time.
I appreciate some still enjoy the traditional DSLR viewfinder but in all honesty, I don’t miss the viewfinder or DSLR’s at all. Why? With my Sony A9ii
For work, for me anyway, it’s mirrorless all the time with the A9 series, Leica M and Q. I prefer Leica for non work but it still gets used a lot for landscape stuff. I’ve long since lost the nostalgia for DSLRs
Choosing the ‘right’ moment, has always been part of photography - with whatever medium - from Collodion to Safety Film to Digital - or camera system - from Plate camera to Box Brownie, via SLR’s to Mirrorless - is used.
That’s the art or skill - timing - and F8
PS. Like my Naim hifi, I am in the Cheap Seats - with just one camera - a Nikon D7000. And just like hifi, its always possible to solve problems with more money & more kit… If you have the money.
I got hold of a D7200 and it’s a fantastic little performer for the money. I nearly sold my D800 and kept the 7200 but in the end decided against it as my FF lenses - 24-70mm and 70-200mm - would not be used to their full potential.
Having always had Nikon gear, the main reason I do not upgrade to mirrorless is that I hardly use my current kit anyway.
My D7000 was bought to quickly replace my failed (and un-economic to repair) Full Frame D700… 
I wasn’t fussy if I got a D7000, a 7100 or a 7200 - but I found a D7000 first (and older = cheaper). Works. Don’t use it much… sadly. I still have some of my FF lenses…
(IMO - the D7000 series is the sweet spot in the Nikon range. They work with nearly all the lenses, old or new. Theyu are not too big and have most of the controls I need. No so different from my previous D700 or D200.)