The Zenfone 3 Max has a 16 megapixel 1/3-inch sensor on the back with f2.0 aperture lens. It uses Asus TriTech AF, which is a combination of contrast detection, phase detection, and laser autofocus systems. There's also a dual LED flash with a white and an amber color LED.
The Camera application on the phone is quite comprehensive, with several modes, including a Manual mode that lets you manually control the shutter speed, white balance, ISO, and focusing. The controls are all well laid out and if you're in the Auto mode the app will also suggest you to switch to an appropriate mode such as HDR or Night depending upon the situation and provide a quick switch at the bottom that you can just tap to switch to that mode instead of digging through the Mode menu.
As for the image quality, the rear camera produces generally good looking images. The colors look good and so does the contrast and white balance. And this is in the Auto mode with the optimizations disabled. Image quality is on par with, if not better than the Redmi Note 3. Where things fall apart for the rear camera is in dynamic range, which is exceptionally poor on the Zenfone 3 Max. It frequently blows highlights on brightly lit objects and this despite bringing down the exposure where everything else is almost black. The Redmi Note 3 actually does a lot better in high contrast situations. The HDR mode on the Zenfone 3 Max does help quite a bit so it's worth keeping that on almost every time you're outdoors under bright light.
Another area where the Zenfone 3 Max failed was in autofocus. This could just be an issue with the current firmware but the phone kept hunting for focus constantly while shooting, which meant half of our shots came out looking out of focus. Hopefully, Asus fixes this in an update.
The 1080p video also suffers from the focus hunting and the poor dynamic range of the camera to a degree. Also, the electronic image stabilization only works at 720p resolution and not at 1080p.
The Zenfone 3 Max has a 4100mAh battery, which is pretty much the main feature of the phone. The battery life is undeniably impressive, with 6-7 hours of screen-on time and upwards of 24 hours of overall use combined with standby.
The most advertised feature of this phone is that it can also be used to charge other devices. It ships with an OTG adapter that you can use to charge, perhaps, your other phone or a tablet or your smartwatch.
Unfortunately, the rate of charging is very slow. We plugged in an iPhone 7 Plus which was at 1%, and after an hour it had only charged to around 17%. The Zenfone 3 Max meanwhile went from 100% to 87%. As such, it's really only meant to be used when you desperately need to charge something and have power to spare on your phone, and also happen to carry the adapter around.
Meanwhile, the phone itself also doesn't support fast charging. With the supplied 5V 2A charger, it takes two and a half hours to charge the battery completely.
The Asus Zenfone 3 Max is a decent all-round product, with a good mix of features and performance. The design is good and the phone feels well built. The display quality is impressive and one of the best in its class. The performance for day to day is adequate and the battery life is excellent. It also ships with a fairly decent set of cameras. Overall, nothing that will blow you away but pretty good nonetheless.
Unfortunately, Xiaomi has Asus beat in the value for money department, with a much lower price tag in markets such as India and a significantly better processor. Everything else is pretty much on par between the two phones. As such, it's hard to recommend the Zenfone 3 Max when the Redmi Note 3 is around.