Exposure difference between normal and live view

lin

I have a Canon T3i and a very good preset 500mm preset lens. In "live view" (mirror up) it exposes correctly. In normal view (mirror down) overexposes by 1 or 2 stops. Metering mode is set to "evaluative" and everything else is equal (tripod and wired remote shutter release).

Any ideas?

PBked

Hi @LIN,
I am not sure why your mirror lens does this as I am not technical. It could be something to do with the difference between contrast detect in live view and phase detection in viewfinder operation. However, the fact that you have discovered it means that you can use your exposure compensation button when using the viewfinder and set it to zero when using live view. If I turn up any answers, I will repost.
Regards,
PBked

lin

Thanks.

Through the help of Steven at the Canon support group, I have learned that you are partially correct.

The rest of the story is that in Live View and AV mode, the camera measures the light falling on the recording sensor and determines the correct shutter speed for its estimate of the best overall exposure, regardless of the aperture. In Viewfinder mode, the light is not hitting the recording sensor, but an auxiliary array of sensors, and, further, it does not disregard aperture but makes an educated guess at that f-stop before setting shutter speed.

Depending on its guess, the image will be underexposed, properly exposed or over exposed, almost randomly and there is no way to predict which of these it will, so there is no way know the proper offset.

AV Live View works (as I found out), but the advice was to switch to Manual mode and set the actual f-stop of the lens, then adjust the shutter speed either by watching the light meter bar, or by using one of the old film camera rues of thumb (e.g. 'sunny sixteen' says that on a bright day, set the aperture to f/16 and shoot at a shutter speed equivalent to the speed of the film, or ISO in the DSLR case ISO-100=1/100; 'loony eleven' says shoot the bright moon at f/11 with a shutter speed equal to the ISO - ISO 200 would be 1/200, and so forth extrapolating to accommodate limits to f-stop, ISO or shutter speed).

These types of rules are bent in obvious directions for brighter or dimmer subjects.

bruto

If you're using a tripod, are you covering the eyepiece? I would have expected light coming in to cause underexposure rather than overexposure, but it is one variable that should be considered when shooting in either mode, even though the effect in both modes would normally be the opposite of what you're seeing.

My experience is only with Nikons, but the metering is usually different between the two viewing modes, and on Nikons at least, the metering menu itself changes. I'd make double sure that you're setting the metering right in both modes separately. I think it's not unusual to get a stop or so of difference, but two is excessive.

PBked, if the lens is a preset, it's probably not a mirror lens, as such usually have no aperture settings at all except for filters. I was going to suggest that a mirror lens might cause odd meter behavior, but I doubt that's the case here. It also occurred to me that if there's a shutter button exposure hold, it might require re-metering after you shut the aperture down, but thinking about it, a problem there ought to show up as underexposure, not overexposure.

PBked

Hi @Bruto,
@LIN did in fact state in her original post that the lens was a preset, but then mentioned the camera's mirror up and down. My brain amalgamated the two and I had a 'senior' moment. I totally agree that if it had been a mirror lens, then the problem would more likely be underexposure.
Best regards,
PBked

bruto

No worries there.

It is an interesting issue, because it's hard to pin down why it might be happening, and most of the possible scenarios I can think of would produce the reverse effect. A lens that vignettes badly might give overexposure if the metering pattern is wide, and puts too much weight on the edges.

But I guess Lin has gotten around it all right. I don't know my Canon nomenclature and features very well, but wonder if more accurate metering could be had by switching to spot or center weighting.

lin

Everything Canon support told me was spot-on, and can be verified if someone wants to fool with it (I did, just to make sure I had tracked the beast to the end, but I only recommend it to them with a bunch of time on their hands and no model railroad). I consider the case of the "Sign of the f/8" to be solved.