I'm learning to use a light meter for a film photography and faced a problem today: when I set exposure to what light meter told me to, image was way overexposed, like 2 stops at least.

Details: Night time cityscape, shot at ISO 100 f/11 with Canon EOS R5. Light meter is Sekonic 758D, used both spot metering and "sphere" mode (not sure of correct term). When I measured for what I assumed to be mid-lit point of my composed scene, I got really overexposed image.

I've read that according to DXOMark measurements actual ISO is lower then camera tells me, which is weird as I'd expect image to be underexposed, not overexposed.

Am I doing something wrong?

  • \$\begingroup\$ IMHO Canon EOS R5 is not film camera. usa.canon.com/shop/p/eos-r5?color=Black&type=New \$\endgroup\$ Dec 23, 2023 at 21:30
  • \$\begingroup\$ @RomeoNinov it sure isn't, I use it to check if I should trust light meter as I see image after exposure. \$\endgroup\$ Dec 23, 2023 at 21:37
  • \$\begingroup\$ For night scene you should intentionally underexpose because lightmeter (in camera or external) assume the exposure should be 18% gray. And in the night you see mostly dark :) \$\endgroup\$ Dec 23, 2023 at 21:40
  • \$\begingroup\$ @RomeoNinov so basically that means I measured with spot meter for the wrong point, like instead of something in zone V, I probably measured for something in zone 3, right? \$\endgroup\$ Dec 23, 2023 at 21:45
  • 1
    \$\begingroup\$ Just FYI, for longer night-time exposures, using a digital camera like the R5 to test your meter for film use is ignoring that film has reciprocity failure while digital doesn't. \$\endgroup\$
    – inkista
    Dec 24, 2023 at 18:46

2 Answers 2


Let me use a different scenario, a studio setup.

The incident light meter (sphere) measures how much light comes to a scene. The incident light knows nothing about your product's color on the table. It can be some white shoes or black ones.

But a reflected light measure is affected now by what the object on the table is, but the measure does not know what it is. Does not know if it is a white or black object, so its goal is to assume it is gray.

I read your comment on the zone system. And you are right. The zone system gives us a hint on what tone overall is what we are seeing and provides that information to whatever setup we are dealing with.

enter image description here

In this case, the compensation means that we are not seeing a green grassfield during daytime, which we could expect to turn gray on a black-and-white photo, but a nighttime when we need that zone to be mostly black.

The same would be true when measuring a white beach zone or snow, or if we need a high-key photograph or low-key one.

On a cityscape is quite hard to define where the midpoint is. You probably have deep blacks, but that depends on if there is haze, clouds, full moon, etc. And you probably have strong lights that are expected to blow the whites, but we do not really know the intensity of them.

It makes no sense to measure a dark spot and define it as a zone 0 because it tells you nothing about how deep the deep black is. So in some cases, IMHO, the spot metering is not really useful, unless you really have an illuminated zone, like a specific wall that is on the frame. Otherwise, it is probably a good idea to adapt a generic rule like the Sunny 16 rule and compensate for the necessary EV steps.

  • \$\begingroup\$ First of all, thanks for providing me with the correct term - "incident metering". Second, yeah, later that evening I checked some videos and found out that it is advised to check several, at least three spots of landscape, and determine where you want it in terms of eleven zones. \$\endgroup\$ Dec 24, 2023 at 16:38
  • \$\begingroup\$ Buy daytime landscape is different than night. During the day you do expect several places to have a defined value. At night it is more relative, so you need to apply a less specific approach. \$\endgroup\$
    – Rafael
    Dec 24, 2023 at 19:27
  • \$\begingroup\$ At night you generally have to expose to keep from blowing out the highlights, and let everything else fall where it will. \$\endgroup\$
    – Michael C
    Dec 29, 2023 at 5:28

Incident metering (the sphere) is used to measure the light falling on a scene. It has (almost) no use for a night cityscape as the lights in the scene are the source; they are not reflecting the light falling on them.

The spot metering of the handheld is very specific (1˚) much more so than the spot metering of your camera. It can be very difficult to find something midtone; especially in a night time cityscape.

Instead of trying to find something you think is average grey, simply pick something you want exposed to a certain level. E.g. spot metering a neon sign... you know you want it to expose bright, but not clip the highlights; so add ~1.5 stops more exposure than the meter tells you. Similarly for something you want to expose near black but not clipped; reduce the suggested exposure by ~1.5 stops.

The ISO of the camera is not less than reported. DXO is simply using a different standard to measure the ISO (SOS) than the standard the manufacturer is using to report it (REI); there are at least three different standards for determining ISO sensitivity. REI might be the most vague of the standards, but it might also be the most useful/practical for describing the raw sensitivity characteristics of a sensor.


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