1. Download one of the ruler files here:
IMPORTANT: Make sure to print out the ruler at 100% size, do not scale to fit.
2. Cut out the ruler and wrap around the focus ring of your lens. Make sure to wrap it around the focus ring, not other parts of the lens such as the filter
3. Record the measurement of your focus ring's circumference. The following chart will help you understand which ring to select. If more than one lens gear fits your lens, you can use either, but we recommend using the larger of the two.
| If your lens circumference is within | Your Redrock Lens Gear Size is |
| 180mm-220mm | Size A |
| 211mm-250mm | Size B |
| 241mm-280mm | Size C |
| 280mm-320mm | Size D |
IMPORTANT: Your measurement should be the lens circumference, NOT the diameter, and NOT the filter size.
Canon EF (EOS) Lenses
If the table indicates your lens can be used with more than one Redrock lens gear, you can select either lens gear, but we recommend the larger one.
| Canon EF Lens | Lens gear |
| 14mm f/2.8 L | B |
| 16-35mm f/2.8 L | B,C |
| 16-35mm f/2.8 L II | B |
| 17-35mm f/2.8 L | B |
| 20-35mm f/2.8 L | B,C |
| 20mm f/2.8 | B |
| 24mm f/1.4 L | C |
| 17mm f/4.0 Tilt Shift Lens | C |
| 24mm f/3.5 Tilt Shift Lens | B,C |
| 45mm f/2.8 Tilt Shift Lens | B,C |
| 90mm f/2.8 Tilt Shift Lens | B |
| 24mm f/2.8 | A |
| 28mm f/1.8 | B |
| 28mm f/2.8 | A |
| 24-70mm f/2.8 L | C |
| 28-70mm f/2.8 L | C |
| 24-105mm f/4.0 L IS | C |
| 35mm f/1.4 | C |
| 35mm f/2.0 | A |
| 50mm f/1.8 | A |
| 50mm f/1.4 | B |
| 50mm f/1.2 | C |
| 50mm Macro f/2.5 | A |
| 100mm f/2.0 | B |
| 100mm Macro f/2.8 USM | B,C |
| 100mm Macro f/2.8 | B |
| 135mm f/2.0 | B,C |
| 85mm f/1.2 | D |
| 85mm f/1.8 | B |
| 70-200mm f/2.8 L | C |
| 70-200mm f/2.8 L IS | C |
| 100-400mm f/4.5-5.6 L IS | D |
| 180mm Macro f/3.5 L | B,C |
| 200mm f/2.8 L | B |
| Zeiss Distagon f/3.5 18 mm Lens with T* Coating for Nikon ZF mount | A |
| Zeiss Distagon f/2.8 25mm Lens with T* Coating for Nikon ZF mount | A |
| Zeiss Distagon f/2 28mm Lens with T* Coating for Nikon ZF mount | A |
| Zeiss Distagon f/2 35mm Lens with T* Coating for Nikon ZF mount | A |
| Zeiss Planar f/1.4 50mm Lens with T* Coating for Nikon ZF mount | A |
| Zeiss Planar T* 1,4/85 ZF.2 Lens | B |
| Zeiss Makro-Planar T* 2/100 ZF.2 Lens | B |
Nikon F Mount Lenses
If the table indicates your lens can be used with more than one Redrock lens gear, you can select either lens gear, but we recommend the larger one.
| Nikon Lens | Lens gear |
| Nikon AF-S NIKKOR 14-24mm f/2.8G ED | C |
| Nikon AF-S NIKKOR 24-70mm f/2.8G ED | C |
| Nikon AF-S Nikkor 70-200mm f/2.8G ED | C |
| Nikon AF Nikkor 14mm 2.8D ED | B,C |
| Nikon AF Fisheye Nikkor 16mm 2.8D | A |
| Nikon AF Nikkor 50mm F1.8D | A |
| Nikon AF-S Micro Nikkor 105mmVR f2.8G ED | C |
| Nikon AF DC-Nikkor 105mm f2 D | B,C |
| Nikon AF Micro Nikkor 200mm f4 D Macro Lens | B,C |
| Nikon AF VR Nikkor 80-400mm f4.5-5.6D | D |
| Zeiss Distagon 3.5/18mm ZF | A |
| Zeiss Distagon 2.8/25mm ZF | A |
| Zeiss Distagon 2/28mm ZF | A |
| Zeiss Distagon 2/35mm ZF | A |
| Zeiss Planar 1.4/50mm ZF | A |
| Zeiss Planar 1.4/85mm ZF | B |
| Zeiss Makro-Planar T* 2/100 ZF.2 Lens | B |