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I have been working on a technique to produce a timelapse series of the sunset and am trying to use Aperture Priority since the lighting changes so rapidly. I am using a Canon 6d with a Rokinon 24mm lens that has no electronic connection to the Camera. While the 24mm is a fantastic landscape lens it is very soft at low focal ratios and even alittle soft at f/8, so I am using f/11. The camera is set to an ISO of 200 and of course the camera determines the exposure length in aperture priority.

All of my images are severely underexposed and admittedly I have not played around with ISO, but as I understand it, if I increased ISO, the camera would only decrease the exposure length by an equivilent number of stops to produce the same underexposed image. How can I get Aperture Priority to produce a properly exposed image with a mechanical lens like the Rokinon that is set to a modest aperture and has no electronic connection to the camera.

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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.

  • So after allot of experimenting I figured it out. In the absence of a connection the camera determines aperture based on the electrons produced in the electron wells per a time constant prior to pushing the shutter. Even if you change the aperture it will still give the exact same underexposed image because it registers a different number of electrons indicating a different amount of light hitting the sensor. However, you can exposure by using the bracketing to tell the camera to add 1 to 3 stops to whatever it determines. – Jon May 22 '14 at 3:41
  • @Jon: I find it unlikely that's the case, since the sensor is not exposed to light prior to actually opening the shutter. The metering sensor, however, which is an entirely different sensor housed in the upper part of the camera where the pentaprism is, does get light, and it is responsible for determining exposure. I am quite certain my description is correct...the lens is not communicating with the camera, so the camera is assuming an aperture, and that aperture is incorrect for all but one aperture setting (i.e. if the camera assumes f/4, and you choose f/4, ONLY then would the camera... – jrista May 22 '14 at 4:12
  • ...meter correctly.) There isn't any magic going on with pixel wells or anything like that, because the sensor literally is blocked by the shutter until the shutter opens...at which point there is no longer any time to do metering, as you are ACTUALLY taking an exposure. I would also offer that bracketing your shots is only a bandaid for your problem, it is not a solution. Your BY CHANCE possibly, maybe, getting a better exposure, but you will never get the right exposure until you go full manual. Full manual is your only option here. – jrista May 22 '14 at 4:13
  • I disagree with that, when you go full manual at some point you will have to adjust the exposure, iso or aperture to compensate for the decreasing light during sunset and the bright ambient light (i.e. the sun) will bleed over into the adjacent wells and increase in diameter abruptly from one shot to the next and there is nothing you can do in post processing to fully compensate for that. I just shot an aperture priority time lapse with exposure compensation tonight and it worked perfectly over a 2 hour long time lapse. – Jon May 23 '14 at 5:43
  • Shooting in AV allows the camera to adjust from one photo to the next to get a much smoother transition as opposed to waiting until the light drops by half or a full exposure and doing it manually. – Jon May 23 '14 at 5:44

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