Can infrared AF assist help a Nikon DSLR focus in very low light?
Asked 11/25/2020
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I shoot badgers at dusk with a Nikon D500 and a 200mm f/2. As it gets dark, autofocus becomes unreliable. Since the D500 uses a separate phase-detect AF module through the viewfinder, I’m wondering whether an infrared light source could help the camera focus without using visible light. Would this work on the D500, and is it different from mirrorless cameras or Live View, where focusing is done at the imaging sensor?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
5y ago
2 Answers
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One possible useful answer is that Nikon speedlights add an infrared focusing assist LED, which gives several times greater useful range than the white LED on the camera. I don't know the maximum range, but I know 50 feet will work fine on a SB-800 to allow focus in the dark. The camera focus indicator must be moved to the center position on the screen for the Assist to operate. The LED is red in the dark, but really hard to see in indoor light.
If you don't want the hot shoe flash to fire then, those flash models with Commander can operate as Master, but with Master Off (group M mode set to --- is Off), and it will still assist focus with infrared.
Originally by user38978. Source · Licensed CC BY-SA 4.0
user38978
5y ago
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Generated from our catalog & community — verify before relying on it.
Yes—on a DSLR like the Nikon D500, infrared AF assist can help in very low light.
A practical Nikon-specific solution is to use a compatible Speedlight with AF-assist. Nikon flashes such as the SB-800 project an infrared/red assist pattern that can greatly extend focusing ability in the dark; one user reports it works fine at around 50 feet. On Nikon bodies, the AF point usually needs to be set to the center point for AF assist to operate.
If you don’t want flash exposure, some Nikon Speedlights can still provide AF assist while the flash itself is disabled by using Commander/Master mode with the master flash output turned off.
Your concern about mirrorless/Live View is reasonable: when focusing is done at the imaging sensor, an external IR AF-assist beam may be less useful or unsupported compared with the DSLR viewfinder AF system, which uses a separate AF sensor.
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