Teleconverter Calculator
See how a teleconverter changes your lens's effective focal length, aperture, and light transmission.
Original
With teleconverter
Aperture
effective f-stop
Light loss
stops of exposure
Magnification
increase vs without TC
TC selected
AF compatibility depends on your specific lens and body combination. Check the manufacturer's lens compatibility list before buying a teleconverter.
What a teleconverter does
A teleconverter (TC) is an optical element that fits between the camera body and the lens, magnifying the image circle produced by the lens. A 1.4× TC makes a 100mm f/4 lens behave like a 140mm lens; a 2× TC turns it into a 200mm equivalent. The trade-off is reduced maximum aperture and light transmission.
Aperture and light loss
A teleconverter does not change the physical aperture of the lens — the iris stays the same size. But because the image is magnified, the effective f-number increases by the same factor as the magnification. A 1.4× TC multiplies the f-number by 1.4 (one stop of light loss). A 2× TC doubles the f-number (two stops of light loss). This is a fixed optical consequence, not a camera setting.
M43 teleconverters
- OM System MC-14 (1.4×) — works with OM System and Olympus PRO lenses. AF is maintained on compatible bodies.
- OM System MC-20 (2×) — works with select PRO lenses. AF maintained on compatible bodies, though the camera may require a brighter scene to lock focus reliably due to the two-stop light loss.
- Panasonic DMW-TC14 (1.4×) — compatible with specific Panasonic M43 telephoto lenses including the Leica DG 100-400mm and Leica DG 200mm f/2.8.
- Panasonic DMW-TC20 (2×) — compatible with specific Panasonic M43 telephoto lenses. Check Panasonic's compatibility PDF for your exact lens.
Magnification
The maximum close-focus magnification of the lens also increases by the TC multiplier. A lens with 0.25× maximum magnification becomes 0.35× with a 1.4× TC and 0.5× with a 2× TC. This is a useful side effect for macro work — teleconverters are sometimes used specifically to increase magnification at close focus distances.
AF in low light
Most modern M43 bodies can autofocus through a 1.4× TC with a reasonably fast lens. A 2× TC is more demanding — the effective aperture is narrower, so the AF system receives less light. Phase-detect AF on bodies like the OM-1 handles this better than contrast-detect only systems. In dim conditions, expect AF to be slower or less reliable with a 2× TC.