One's light and one's dark

[wibble]

Hello .. just been testing out my Christmas present .... experimenting taking some pictures at different exposures of a street light.

Sometimes I got pictures what I expected with the lamp lighting the surrounding area ..and sometimes all I captured was the lamp itself and the surrounding area was dark.

Now in the attachments I think I kept to the same settings and focal point position ... is it logic what was causing the different exposures?

[Shadowman]

Hi Viv,

It would help if you posted camera settings (ISO, aperture, shutter speed) and focal point. If camera settings were the same and camera set at PSAM or even auto mode then point of focus would explain difference. Another fun exercise would be to put the lamp post (light source) at your back and use it to photograph other subjects in lowlight. Also, I assume there was another lamp post directly behind you when you shot these?

[wibble]

Hi ..have attached settings of the two pictures using aperture mode ...focal points need to find some way to show those but they were towards top of pole. There was no light behind me ... this street light was the only source of light. Does this hep at all

Hi Viv,

It would help if you posted camera settings (ISO, aperture, shutter speed) and focal point. If camera settings were the same and camera set at PSAM or even auto mode then point of focus would explain difference. Another fun exercise would be to put the lamp post (light source) at your back and use it to photograph other subjects in lowlight. Also, I assume there was another lamp post directly behind you when you shot these?

[Manfred M]

Welcome to the wonderful world of light metering Viv!

This is a "feature" with any camera light meter, as their default setting assumes that every image that you shoot be "average". This tends to work quite well in many daylight settings, but breaks down in scenes like the one you are shooting, where the lighting is anything but that. A night shot, where you are shooting towards the light source, definitely falls into that category.

With the metadata you have posted, the first thing that jumps out is that you changed metering modes between taking the the shots. In the first shot you used matrix metering mode, which takes light readings from a number of areas in the images and uses them to calculate the exposure, so the light itself, things that the light has hit as well as the dark background are all used to compute the exposure. On the second shot, you switched to centre weight metering mode. Here the light meter bias the exposure to what is in the centre of the viewfinder and the further away from the centre that you get, the less impact it has on how the exposure is calculated. There is probably a third metering mode referred to as "spot metering", where the exposure is calculated purely on what the light at the tiny spot right at the centre of the viewfinder is showing.

All three will bias the exposure calculation differently. Matrix metering is probably the most common metering mode most people use and they will switch to spot metering for very specific reasons (getting the exposure of a person's face when the shot is back-lit is where I will switch to it). Centre weighted is a fairly old approach and I know very few people who still use it; it has largely been replaced by matrix metering.

The other reason you would be getting different exposures is that you have used a different focal length, so in the second shot there is far less dark area than in the first and that would definitely require a different exposure.

[Cantab]

Viv,

Welcome to CiC. I'm going to add a comment that Manfred and other experienced night photographers will hopefully expand upon or correct.

As Manfred noted, exposure meters try to turn everything into average daytime lighting. But that's not what you want for night time work. So one option is to use automatic metering to get you into the ballpark but then to switch to manual. That way you'll have a lot more control over the end result and any experimenting you do will yield consistent results.

[dje]

Now in the attachments I think I kept to the same settings and focal point position ...

Hi Viv

You haven't actually got the same settings. The shutter speed in the first image is 1/50 sec and in the second you have 1/5 sec. Hence the different exposure. You have used Aperture Priority mode in which the shutter speed will be adjusted by the camera according to the metering it has done. Manfred has explained why the metering is different in each image.

Dave

[loosecanon]

One needs to remember that mains powered lights flicker with variable light output at the mains frequency, in UK 50 times a second. Whilst not seen because of hunan eye response latency, it will affect a scene lit by mains powered lights. This effect is even greater with some LED lights.
The camera will meter just before exposure and so the scene it meters from may be lit differently from the scene during exposure. This effect will be more noticable the shorter the exposure time.
The solution is to ignore the camera meter, set manual, use a slowish shutter speed to average out the light flickers, or just take lots of shots, and use the screen to determine the correct exposure parameters.