The Sony E 70-350mm is a telephoto zoom designed for APS-C cameras, while the FE 100-400mm GM is a premium zoom designed for full-frame cameras. Your sensor size matters most. On an APS-C body the 70-350mm gives a very long field of view in a small package, and the 100-400mm GM is a heavier, higher-end alternative.
Sensor Size Changes the Math
An APS-C sensor crops the view, so a 350mm lens on APS-C frames like roughly 525mm on a full-frame body. That means the 70-350mm can deliver reach comparable to or greater than a 100-400mm on full frame, in a much smaller lens.
The 100-400mm GM covers a full-frame image circle. It can also be used on APS-C bodies, where it behaves like roughly 150-600mm, but it is bigger and heavier than the lens made for that sensor.
Main Differences
| Trait | E 70-350mm | FE 100-400mm GM |
|---|---|---|
| Designed for | APS-C bodies | Full-frame bodies |
| Size and weight | Compact and light | Larger and heavier |
| Positioning | Value-minded telephoto | Premium G Master |
| Strength | Portable reach | Build and optical ambition |
Check each maker’s page for current weights, apertures and compatible converters.
How to Decide
- Your body: if you shoot APS-C and expect to stay there, the 70-350mm is the natural match.
- Future plans: if you may move to full frame, the 100-400mm GM will carry across, while the APS-C lens would work only in a cropped mode.
- Weight: long outings favour the smaller lens.
- Demands: for professional action work with tough conditions, the GM design is aimed at that.
- Resolution: a full-frame lens on an APS-C body may use only part of its image circle, so you gain little over a lens designed for that sensor.
As a general baseline for animal and bird movement, a shutter speed of roughly 1/1000 and faster is a sensible choice at these lengths.
Effort matters too: a smaller lens often means a smaller bag, a lighter strap load and a quicker setup, and those traits keep you shooting longer. Premium glass brings its own appeal, with a sturdier barrel and more control options, but only if you will use them. Be honest about your habits, and choose the lens that fits the way you really work outdoors.
FAQ
Can the 70-350mm be used on a full-frame body?
Most full-frame Sony bodies can mount it, but they switch to a cropped mode that uses only part of the sensor, which lowers the resolution of the final image.
Which has more reach on an APS-C body?
The 100-400mm GM reaches an equivalent view of about 600mm on APS-C, compared with about 525mm for the 70-350mm. The difference is modest next to the size gap.
The Short Version
For APS-C shooters, the 70-350mm gives portable reach. For full-frame shooters or those planning to move, the 100-400mm GM is the higher-end choice. Match the lens to your sensor first.
