Why are my Canon 6D aperture-priority shots underexposed with a manual Rokinon lens?
Asked 5/20/2014
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I’m shooting a sunset timelapse on a Canon 6D with a Rokinon 24mm lens that has no electronic contacts. The lens is set manually to f/11 because it’s softer at wider apertures. In Av mode at ISO 200, the camera chooses the shutter speed, but the images come out severely underexposed.
I expected Av mode to compensate for the changing light, but it seems like the camera may not be metering correctly with a fully mechanical lens. Why does this happen, and what’s the best way to get proper exposure with this type of lens?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
12y ago
2 Answers
3
If the lens is entirely manual and has no electronic communication with the camera, then it is very possible that the camera is making incorrect assumptions about what to do with the metered light. Without communications, when you stop down to f/11, the camera doesn't actually know that. It could be assuming a faster aperture, in which case it will choose a faster shutter speed when it really should not.
Even if you boosted ISO, if the camera is making incorrect assumptions about aperture, then your images are still going to be underexposed, because it's still going to choose too fast of a shutter speed.
For an entirely manual lens without any electronic communications at all, if your having metering problems, then you probably just need to go to full manual mode, and choose the shutter speed yourself. Exposure compensation and the metering scale are going to be largely useless.
Originally by user124. Source · Licensed CC BY-SA 4.0
user124
12y ago
0
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With a fully manual lens that has no electronic communication, the camera may not know the actual aperture you’ve set. If it assumes the lens is more open than it really is, it will pick a shutter speed that’s too fast, causing underexposure.
That’s why raising ISO may not solve the real problem: if the metering is based on a wrong aperture assumption, the camera can still choose the wrong exposure.
The practical fix is to stop relying on Av mode and shoot in full Manual mode instead. Set the aperture on the lens, then choose shutter speed (and ISO if needed) yourself based on the camera meter, test shots, or histogram. For a sunset timelapse, manual exposure is often preferable anyway because it avoids exposure jumps from frame to frame.
In short: the issue is likely the lack of lens-camera communication, and the best solution is to use Manual exposure with that lens.
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