How far does a spotmeter reach? AKA. can u spotmeter the horizon

[Sune Bang Ingemann]

Spot metering is meassuring reflected light levels so of course a face, wall, car etc. will reflect a certain amount of light, but the sky is miles upon miles away. I suppose i am just metering the reflection of "air".  Say I wanna do the zone system on a blue hour scene with both some forground and the horizon as the background. Could i just point the spot meter at the sky and trust the numbers?

Best regards

[David Sekanina]

The more distant your objects are, the more the light has to travel through the air and its floating dust particles until it reaches your spot meter. But that's also true for the camera lens, so they see the same amount of haze.

Depending on pollution the blue shift might become a purple or orange shift.

Or did I misunderstand your question?

image by Klaus Leidorf

Edited June 23, 2022 by David Sekanina

[Eric Eader]

Hello,

No matter how far or how close the object you are spot metering is away from you, the meter will show you a mid-point reading for each object (or space), you meter.

Some times the background is brighter than the foreground...  sometimes the reverse. 

You will have to interpret the numbers (Zone System placement), to find what you believe is a proper exposure for that scene.

 

 

 

 

 

 

[David Mullen ASC]

Doesn’t matter how far the source is, both your eyes, the meter, and the camera are reacting to the light that reaches you.

[Bruce Greene]

The scenario you describe is the perfect use of a spot meter.

just keep in mind that the reading you get from the horizon will be the exposure to reproduce that area of the exposure as middle grey.

so if you want your horizon to be bright you’ll need to give it more exposure than the meter reading. If you’re shooting film, that might be two or three stops more exposure than the spot reading for example.

I don’t use my spot meter much these days when shooting digital, but I rely on it for shooting film, especially landscapes.

[David Mullen ASC]

If you are spot metering a day exterior, whether magic hour or in sunlight, you point the meter at what you want to measure and then make a judgement call as to how many stops over or under middle grey value you want that area to be.  If you are shooting at a low angle with people semi-silhouette against a dusk sky, then you'd probably meter the sky and either say that is middle grey or one-stop over in value, depending on the effect you want, and you'd let the subjects go silhouette. If there is less sky in the frame and the people are more important, you'd probably meter their faces and decide how dark they should look at dusk, maybe two stops under middle grey. Just depends on what effect you want, and also if you want to err on the side of less underexposure and further darken it later (or you could effectively do that by rating the film stock slower and shooting a grey card exposed correctly for that lower ISO, so that the transfer will be set to make that look normally-exposed, in effect, bringing down the image in post so that you don't have to underexpose the film quite as much.

[Sune Bang Ingemann]

Thank you guys for the responses. I realized I never replied. 

The question was in regards to a shoot where I was doing a blue hour scene at the end of one day. The producer wanted to know when exactly we could press record on the scene so I was going out every evening with my meter and checking the time (Didn't want to trust the apps). The scene was handheld and two shots that needed to be cut together. I wanted to now exactly how long I could shoot the scene for. It was Mini-LF and Ultra primes, I didn't want to push above 800 ASA because ... I'm a wuss ?

I gave myself som lee-way by starting with a 0.3 nd and T 2.8 and underexposing the whole scene by 1 stop from the begging, I'd readjust exposure according to my lightmeter between every take. By keeping the scene under exposed by one stop, and going throwing the ND and stopping down 2,0, I had around 20 minutes of very even, very nice blue hour scene, with some minor background change (Live in Scandinavia, so we have some long days in the summer). I like to use my meter when underexposing, as I never really know how well calibrated the monitors are, so I am a bit nervous of living and dying by the lut. 

It worked, but maybe it was a bit convoluted. A lot of this becomes second nature with experience I guess. 

In regards to the spot meter your answers makes perfect sense. It's nice to know. Thank you