Metering for Long Exposures

[diputs]

I really like shooting at night. Currently I set my ISO and aperture, then guess on my Shutter Speed. I can usually get pretty close, but waiting on a 2 minute exposure to see what adjustments need to be made can be time consuming.

How do you meter for Long Exposures?

One thought I had was to set my ISO at 12800 and then open the aperture as wide as possible and hopefully the shutter speed will be faster than 30 seconds. Then I can use an iPhone app such as LightMeter or PhotoBuddy to determine my shutter speed when I drop the ISO down to 100 and close down the aperture.

Is there a better way?

[ALSto]

I use manual mode generally and a tripod. So, I 1st start with a ISO100, F16+ and meter against what my main focal object will be a in photo and adjust speed until meter reads 0. It totally depends on the situation but if you use AV mode the camera will decide for you.

For hand-holding, I generally have ISO400 and start at f8 and adjust speed from there depending what my trusty in-camera meter tells me. Here is a sampler hand-held. As you can see I ended up at f6.3 and 1/13s with satisfactory results.

In the case of below I exposed against midpoint in the building where it was lightest.

Make 	Canon 	Model 	Canon EOS 50D
Aperture Value 	f/6.3 	Exposure Bias Value 	0 EV
Exposure Program 	Manual 	Flash 	No Flash
Focal Length 	14 mm 	ISO 	400
Metering Mode 	Spot 	Shutter Speed Value 	1/13 sec

In this example, I exposed on the floor as it was grey tone.

Make 	Canon 	Model 	Canon EOS 50D
Aperture Value 	f/6.3 	Exposure Bias Value 	0 EV
Exposure Program 	Manual 	Flash 	No Flash
Focal Length 	10 mm 	ISO 	400
Metering Mode 	Spot 	Shutter Speed Value 	1/2 sec

Both are terrible examples to show you because technically I should have been using a tripod at such low exposure speeds however they worked out for personal consumption.

Allen...

[tday01]

As a working professional for over 30 years I have found that a hand held meter is the quickest and best way to achieve accurate exposures when your exposures are 30 seconds or longer.
There is a factor called reciprocity failure which you need to consider when using long exposures. Generally speaking this means that you will need to expose your image up to 100% longer than your normal exposure would require when your exposures are 1 minute or longer.
The only way to figure this out is through experimentation. Thus the need for a hand held meter, and keeping accurate notes, until you figure it out. Until then you are still just guessing. Terry ]

[inkista]

Originally Posted by tday01

... There is a factor called reciprocity failure which you need to consider when using long exposures....

... if you're shooting film. Digital doesn't have reciprocity failure--instead, digital has increased "hot" pixel noise instead. Usually taken care of with dark-frame processing, either in-camera or in post-processing. But there is no curve to the shutter speed, as with film.