Admittedly, my primary reason for switching to a mirrorless camera system was size and weight, with the full understanding that this is in regards to camera body and batteries only, not lenses.
Please forgive the camera images as this body just got back from a 3 month long, overseas trip, so its a little beat up!
Metal and glass; that is all that the Sony Alpha A7s and the accompanying Zeiss lenses are made of. The Added durability of using metal is worth the extra weight.
Optics are no joke
Very few compromises can be made in high quality lens design and Sony / Zeiss faced some serious challenges when designing the new line of lenses for their full frame (FE mount) glass such as flange distance. NEVER BEFORE has any company attempted to make a high quality, full frame and 4K video capable lens line with such a short distance between the mount and the sensor. While amazing in its own right, Fuji's micro four thirds lenses do not need to cover such a large sensor.
Luckily Zeiss had a template
Zeiss employed element groupings from decades ago such as Biogon and Distagon and made some tweaks to get them just right. The resulting lenses were the same size as DSLR glass and that was OK. There is no compromise made when optical image quality is at stake. To let more light in, you need larger front elements!
Knowing all this before jumping ship and moving over 100% to SONY Alpha, I went with the A7s for insane low light efficiency. The added bonus of small file size (12 mb full frame RAW files!) that are reminescent of the 5D Classic. YES PLEASE!
My future plans include adding the A7R body as a compliment for longer lenses used in APS-C mode (the extra resolution makes a huge difference) and also when image quality is at the highest priority, such as my fashion and product work. This post is only referring to use of the original A7s.
ISO flexibility like no other camera
I have always been a proponent of "telling the camera what to do" and "the photographer determining what settings to shoot every image" these are a very common phrases in my writings, workshops and 1 on 1 lessons. This is of course all as opposed to allowing the camera to determine what your image looks like. For example, this means shooting at f8, 1/125 when the final image you want, neeeds to look like it was shot at f8 and 1/125 of a second. There really is no other way to do it because if you need more light, both slowing down the shutter and opening up the iris will change (even ever so slightly) what the final images looks like.
Shooting with a camera like the A7s allows me to set the camera how I want, then use a very wide range of available ISO to adjust the exposure with little or no consequence on image quality. In my opinion, ISO 50-12,000 are very useable before significant noise becomes present; and when noise DOES begin to show up, it is far more pleasingly added than previous cameras that I have owned. Even though the noise quality of the A7s is a bit too colorful to be considered 'pleasingly grainy', in many ways it echoes that produced by the 5D classic that I mentioned earlier and adore so much.
Having this large of a range of usable ISO has simplified photography for me, for the better.
Even though I have always approached my photography this way first, very little gear that I have owned and shot with has allowed it to become this easy. I am a huge fan of the Sony A7 series and I am looking forward to see where it allows me to take my work.
I was not compensated in any way to write this post. Happy shooting!