I've been searching for a resolution to my lower light problem that wasn't going to cost a fortune, or three. I found a couple of solutions that might work:
Nikon D750 + Tamron 15-30mm f/2.8
Nikon D7200 + Sigma 18-35mm f/1.8
At least, US$2000 was required for a solution that wasn't often needed. You see, I don't photograph at indoor skate parks much. The solution could help me with indoor gyms and swimming pools and similar situations with poor lighting, but those situations aren't a huge part of my life right now, unlike two years ago.
What's wrong with my current equipment? Panasonic and Olympus aren't getting the best sensors from Sony, and at a pixel density similar to APS-C at 24 MP, you don't have a lot of luck. Even the D7200 is not a great substitute right now but it may have enough of an advantage, if I find a bigger need. In my experience, the Panasonic GH4 is doing well at ISO 3200 with 1080p video but neither the GH4 or Olympus E-M1 did well with photos. (Take this as I consider it. If you can't print above 4x6 inches, I don't consider it good image quality. If you can get 11x14, 11x17, or 13x19 prints from an image, great!)
The D750 would be a much better substitute, but considering that the cost would be US$3500 plus tax, it is even more risky in making my money back.
Therefore, I'm doing something that even I didn't expect. I'm buying a Pentax K-50 body, now with kit lens, flash, and SD Card for US$419. Yes, that doesn't solve the lower light problem by itself but it's inexpensive enough, and weather-sealed, that I can become comfortable with it before investing even more money. I'm actually buying two. The other is for one of the riders who keeps borrowing my equipment, so that he and his friends can freely make video clips without using me or my equipment as a resource. I don't think that the kit lens is formidable but I've seen plenty of good that's been done with kit lenses on lesser equipment. I'll probably try the equipment as a consumer for a week, just to see how that works.
I've mentioned in the past that Pentax firmware is quirky. Ricoh hasn't changed that, unfortunately, because the company has also had quirkiness of their own. However, they have proven that their images seem quite noise free, and they have been stating a top sensitivity at ISO 51,200 for quite a long time.
The Pentax 16-50mm f/2.8 lens currently $849.95 seems useful, but the Sigma 18-35mm f/1.8 has been on my list. The Pentax lens is weather-sealed and the Sigma lens is not. Generally, weather-sealing is important to me, though indoors, you don't usually have to deal with bad weather, it is sometimes the case. The Pentax lens is heavily discounted and the Sigma lens is selling for a typical full price. The Sigma lens likely will require the dock to fix the calibration issues that seem to come with each lens.
There is also a unique 10-17mm f/3.5-4.5 fisheye lens available from Pentax, currently at $475.95 but on backorder. Obviously, this maximum aperture will not be nearly as useful in lower light situations.
The K-50, however, is a compact body. I don't believe that it's smaller than the Panasonic GH4 and I'm willing to use my older, larger Four-Thirds lenses on the GH4 and they are generally a good combination.
If I've lost my mind, I hope that this is a good insanity. I looked at Pentax back in 2003 and 2004 when the *ist was their digital model, and after looking at Pentax, Nikon, and Canon, I chose the Olympus E-1 body. A lot of time has passed and technology has changed. Further back, I would have bought a Pentax ME Super film camera because it was quite good and the K-mount was new at the time. I was using a FujiFilm SLR at that time, which used the Pentax screw mount, so the two brands were fairly close. Around the same time as the Pentax ME arrived, FujiFilm brought the Fujica AZ-1 to market with Aperture priority automatic exposure--and a K-mount.
Update 2015.04.21: The package arrived with both K-50 bodies. For $419, it included a K-50 body with the 18-55mm f/3.5-5.6 with the newer, plastic lens mounting. It's great that it's a light lens, but I have memories of people with their Canon 300D/Digital Rebel with part of the lens in their hand and the other part still attached to the camera. Obviously, the lens mount itself didn't fail but was it ever ugly in real life experiences.
In the box was also a 4GB EyeFi card. Since the K-50 came standard with support for the card, it should be an easier way to transfer JPEG files to phones and tablets.
The Adorama kit also included a Monster Cable Advanced 32GB SD Card and a Pentax AF-200FG external flash. I'm not certain how reliable the SD Card will be. I always think of Monster Cable products as overpriced junk. Hopefully, it will be fine. Obviously, as part of the kit, it wasn't overpriced. The flash seems good enough, as an add-on to overcome the shadow that might come with the in-body flash and bigger lenses.
The group of items included in the price seemed generous.
This is the first time I've ever owned a lower end dSLR. However, because this one is weather-sealed, it hardly seems at the lower end. In my hand, the body seems rugged and well built. The lens doesn't seem that way, but it seems sufficient for what it is. I wasn't expecting much.
After charging the battery completely, I inserted it into the slot carefully. It doesn't have a typical slot, as it can be powered by four AA batteries. The lithium ion battery fits into the grip, as expected, but it doesn't have a dedicated space.
There was a bit of setup asking me which language to use--Japanese was not an option, unfortunately. It asked for a time zone and whether daylight saving time (DST) was in use. It also asked things like date format, and had me enter the date and time.
After the initial setup, I went through some options. I noticed that the camera came with firmware version 1.00. I'm fairly sure that the firmware update isn't difficult. I was reading something about it earlier. It's only up to version 1.02 anyway.
I really hope that there are fixes to keep the rear display off until I want it enabled. The tiny (~1000 mAh) battery isn't enough to keep the display going that long. Adorama has a price of $44.00 for the original replacement. That seems similar to the Olympus OM-D E-M1 battery, which is small also, and about the same price as the Olympus dSLR battery, which has about 1.5 times the capacity. The Panasonic GH3/GH4 battery is much bigger and about $80.
The menus are just as awful as everyone else's, though they are shorter, so you don't have to scroll vertically. I'm hoping that familiarity will save me at some point in time. While there is a status display, there doesn't seem to be an equivalent to Olympus' great Super Control Panel or Panasonic's Quick Menu, but that may be that I just haven't found it yet. I'd like to say that it is much easier to use than Olympus or any other menus, but I'm not finding that to be true.
I like that they have two custom user sets of settings. Now, I just need to learn to fill those and save the sets.
I've taken a few quick shots, just to see how the auto focus and image quality is indoors and in typical lighting. It responded quickly, but ISO 3200 doesn't seem particularly wonderful with noise reduction disabled. Auto focus seemed okay, even though it apparently doesn't focus lower than EV -2. It should be interesting to compare it to the Panasonic GH4, which focuses to EV -4 but often in good light doesn't focus where I want when there are fences or walls available. As well, the Olympus E-M1 has great face detection and it's great for portraits.
It should be an interesting adventure. I'll first use it in the simplest modes with JPEG files only. I will jump to raw files later and really see if there is a bit difference, other than the 4 bits of color per channel.
Update 2015.04.22: The firmware update was painless, virtually the same as Panasonic's updates work. The exception was that the camera turned itself off, rather than waiting for me to acknowledge that it had completed the update. That left some doubt in my mind as to whether it had finished correctly or terminated abnormally.
Update 2015.04.23: Geez, let me remove the SD Card easily, please! Who designed this contraption that puts the card too close to the door? The card also won't just slide out once it is unlocked. I tried to tilt the body in several directions and the card did not fall.
Also, who designs a camera body to allow it to do video, but makes it difficult to actually take the video? Turn the mode dial to movie mode and press the shutter release isn't difficult, but would a red button on the back be too much to ask? There is a green button on the back panel, but who has green buttons? Pentax, only, apparently has them.
Update 2015.04.26: For a company that doesn't care about video, the video I've seen from the camera looks good. I'm not saying that it's in the same league as the Panasonic GH3 but it's certainly as good as the Olympus E-5 that I have.
The scooter rider who has the same equipment bundle that I'm using has been using it very successfully. He uses it through Live View almost always. I was taking some video for him and I could not see much of anything that was on the rear display. I wasn't even sure when it was taking video.
At one point yesterday, I needed to take a photo from just off the road but there wasn't a place where I could park. He set up my camera to take the shot, and I stopped the car on the shoulder of the road. Unfortunately, he put it in Live View mode, and handed me the camera. It would not focus where I wanted. I couldn't get it to do what I wanted, and I tried several things, in a bit of a panic. I finally found the Live View button and after disabling it, the auto focus went where I expected.
Also, the Eye Fi card is very useful. You need to download the Eye Fi Mobi app for either iOS or Android to be used in conjunction with the card. The K-50 showed the interface as disabled when I first put the card into the camera body. I enabled the card to Auto, within the camera's menu. Then, I started the mobile app and entered setup, entering the activation code. They quickly communicated. I took a few shots and when I accessed the mobile app again, it transferred the photos I had just taken.
The only thing really disappointing with this bundle is the kit lens. The only "kit" lens I've had was more expensive than this whole bundle--the Olympus HG ZD 14-54mm f/2.8-3.5. The Pentax lens isn't horrible. It's exactly what you should expect from a US$100.00 lens.
Update 2015.05.11: I've used the K-50 a few times without taking another camera body as a backup, forcing me to deal with the equipment honestly. It frustrates me each time, naturally.
I don't want the rear display enabled normally but because the battery is so small, I want to save battery life. Pressing the Info button multiple times to turn off the display every time I start the camera is annoying. It can't remember my selection?
The fixed rear display is another source of frustration. However, for the price, I can overlook it. At US$1000-$2000, I would be more frustrated. Still, I can't really shoot at a low angle without some guessing. I'm not really thrilled with the Olympus E-M1's sliding rear display vs the Olympus E-5's fully articulated display.
Most of the other frustrations are typical new-user problems, not a problem with the equipment. The 3:2 format is both not tall enough and not wide enough, compared to my usual 4:3 and 16:9 shooting, respectively, but that is also mostly a new user problem.
Update 2015.07.06: I gave away the K-50 kit about a week ago. Someone I know had their camera stolen and it seemed the best thing to do. I want to overreact about theft in this area but it's not a rampant problem although it is quite noticeable.
I'd handed out the K-50 on several occasions to people with almost no experience with cameras and they did quite well with it. It's very capable for a really good price. The selection of lenses was more of a problem for me than anything else.
Yesterday, I ended up buying the Sigma 18-35mm f/1.8 for US$200 off the regular price. A day earlier, I could have had the Nikon D5500 at US$150 off but I didn't want to buy it for various reasons. I ended up with the D7200 at full price, which is still less expensive than the original D7100 price.
When I went into the store, I pulled out my Olympus E-5 and ZD 14-35mm f/2.0 lens. The D7200 and Sigma 18-35mm f/1.8 is a smaller combination, although the focal length range is shorter and there is no weather-sealing, and it's much easier to design for 18mm than for 14mm.