The Most sad thing about the Whole 1-Series from Nikon is, just HOW far ahead of its time it was. I think people where just not ready for it, and also Nikon did a pretty bad job at marketing with those cameras and propably caused a lot of wrong expectations and confusion and propably also held back a bit too much in some aspects. Just remember the J1 from that series, the original "1" Nikon (Which came out 2012, but dont quote me on an Exact date...), that one did Full Resolution bursts of photos at 10MP Sensor Resolution and 60 Frames Per second. And that camera also allready did 400fps and 1200fps (Just like any 1-Series Nikon) back then on an (kinda) affordable, VERY portable and small, user friendly interchangeable Lens Camera, which is pretty crazy. Problem with the whole system was mostly, that Nikon somehow allways ended up intentionally crippling the Cameras for Whatever reason and somehow never fully commiting to it. That made them Never really catch too much popularity. Problems included, that they never really made a lot of lenses for the System (though the Lenses that are available are INSANELY good!), and also tried seemingly everything to make it difficult for you to use other lenses With the Sysem (For example, the Camera clearly has Focus Magnification, Auto-ISO, Auto Exposure, Focus Assistant and many other things, but they dont work unless with orignal Nikon Glass). And also a few other "little" things like this. This propably ended up frustrating true full-Time professionals who tried it as Workhorses and more serious users (though the system clearly never was intended for that according to nikon), and it propably also was too complicated for those who just wanted to get an point-And Shoot. The small group of people Left to buy the Cameras (at a still rather high price point if you just look at it as an small Photo-Camera in comparison to what was available at the time), then ended up not producing enough sales apparently. You can really tell, that a lot of R&D went into making these Cameras. I took apart quite a few from the J-Series and Modified them, and all of them Are very well made and surprisingly well and Strong built. There is no tiny bit of space Wasted inside, packed full, really nicely built cameras. Then, as they saw that the system somehow never really took off after multiple attempts, they seemingly started an last attempt to kickstart the Sales for the System with the J5, the Last one of the System. They got a ton right with this camera (Ergonomics for the size of camera and general layout is the Best ive ever seen on a camera that "small") and sold it at an rather agressive, competitive price point, but still ended up crippling it to death, and with that, not much later, Nikon sadly decided to discontiue the System Completely. biggest fails in the J5 were that they still continued to disable focus assistants and Automatic Exposure functions for third-Party lenses (the Exposure Meter finally worked with this one), didnt allow for external Flash, the Weird limitations on video (just 15fps on 4K video...? 1/60s Maximum exposure, even at 15 and 30fps...? again no auto-Exposure or auto-Iso -anything for Manual Lenses...and some more), no audio-in and a lot of other seemingly intentionally missing options in the Menu. I know that thats kind of what the V-Series was for (external Flash and Audio-in) but those wherent much better in terms of overall missing functions and also way more Expensive. I never missed the Viewfinder on any of the J-Series however. The Fact that Viewfinders where optional or not even availble on this series of cameras triggered so many people for some reason... As Far as the J5 goes, the Screen is actually that good that you dont even really ever need one and also are WAY more Flexible than if it had one.
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However, its a great system, and they really could have taken this System places with newer sensors and new processors nowerdays. Remember, all the 1-Series Sensors are Sony-Chips from what i know, Nikon usualy gets acces to them after Sony is done building a camera with them (RX-Series in this case) and somehow still end up getting better results out of them then, so, as you said, imagine the Sony RX-Specs on an Camera body of the Same Size with interchangeable lens mount and an Reasonable Amount of buttons and options to make it very useable! I never quite understood, what they actually tried to achive with all the Limitations on those cameras...? Maybe something like Canon is known for doing since many Years, where they intentionally left out functionality on Small, Cheap Cameras to force you buy the Big Cameras if you want certain functions to not make everyone just buy the Cheaper option instead? Never really figured that out, anyways, thats one of the things that killed the System in the Long term. Apart from all the Flaws (which any system in Existence has btw.) ist an amazing, yet rather Pricey System. The System gets a lot of hate in some Places, some is justified, as i explained above, some really not. But anyone i know who actually looked into it and tried it himself, loved it.
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For me (and i looked at quite some Cameras) the J5 is just THE Camera to use. Its not quite "up to date" in terms of latest features anymore, but its also still holds up very well. Overall its a very fun to use and very streamlined Camera. Still havnt found anything nearly as good/nice to maybe replace it at some point, guess i´ll just stay with the J5 for a while.