Which lens when
The overlap-zone decision rule, a table of situations to lenses, and what to do if you can carry only one.
- Decide between the two lenses in the 17-20mm overlap
- Match common situations to the right lens quickly
- Choose a single lens when you can only bring one
Two lenses, one body — the last skill of Part IV is knowing, without deliberating, which one to reach for. Here is how they line up and how to decide fast.
| 10-20 G | 17-70 VC | |
|---|---|---|
| Full-frame equivalent | 15–30 mm | 25.5–105 mm |
| Max aperture | constant f/4 | constant f/2.8 |
| Min aperture | f/22 | f/22 |
| Stabilization | None (relies on IBIS) | VC (optical) |
| Min focus | ≈0.13 m | ≈0.19 m |
| Max magnification | ≈0.14× | ≈1:4.8 |
| Filter thread | 62 mm | 67 mm |
| Weight | ≈178 g | ≈525 g |
| Zoom | Internal, powered (PZ) | Mechanical |
The overlap zone
Your lenses overlap between 17 and 20mm, so in that range you have a real choice. The rule:
- Reach for the Sony 10-20mm when you want the option to go wider, need the smoothest video zoom or breathing compensation, or want the lightest setup.
- Reach for the Tamron 17-70mm when you want the option to go longer, need f/2.8 for light or subject separation, or want its stabilization and close focus.
In short: in the overlap, choose by what you might need next — wider and lighter, or longer and faster.
Situations to lenses
| You are shooting… | Reach for |
|---|---|
| Architecture, interiors, tight spaces | 10-20mm |
| Landscape with a bold foreground | 10-20mm |
| Handheld walking video, vlogging | 10-20mm |
| Portraits, subject isolation | 17-70mm |
| Events and gatherings, low light | 17-70mm |
| Travel, one-lens day, general use | 17-70mm |
| Food, flowers, close-up details | 17-70mm |
| Astro and night skies (fast, wide) | either — 10-20 for sweep, 17-70 for stars at f/2.8 |
If you can carry only one
For a general day, take the Tamron 17-70mm. Its range covers wide scenes through portraits, its f/2.8 handles dim light, and its stabilization and close focus fill the gaps — it is the lens that says “yes” to the most situations. Take the Sony 10-20mm instead only when you know the day is about wide: a city of architecture, a landscape trip, a day of handheld video.
In the field
Before your next outing, decide the day’s one lens in advance based on what you expect to shoot — then live with it. The constraint sharpens your eye and teaches each lens faster than carrying both and dithering. You own exactly two lenses; knowing them cold is worth more than any third.