Design & colour
Macro extension estimate
Estimate magnification and exposure allowance from lens extension.
A clear answer. Here’s how.
Approximate new magnification = starting magnification + extension/focal length. For a symmetric thin lens, effective f-number=N(1+m) and exposure allowance=2log₂(1+m) stops relative to the infinity-focus marked aperture. Real lenses, internal focusing and pupil magnification can differ; no accessory compatibility is inferred.
See a worked example
Worked example
A fixed demonstration, separate from the values you enter above.
- Thin-lens focal length (mm)
- 50
- Additional extension (mm)
- 25
- Starting magnification (image size / object size)
- 0
- Marked aperture f-number
- 8
Example result
- Approximate image/object magnification
- 0.5 : 1
- Effective f-number (symmetric thin lens)
- 12
- Exposure allowance vs infinity marking
- 1.16992500144 stops