Settings for long exposures

[Phil Bennett]

When you guys set up for a long exposure, how long do you set for?

What I mean is, how do you know how long to keep the shutter open, once my camera is past a 30 secs, I guess I need to move into bulb mode, but for how long?. Say a night shot and I choose the aperture, then to set the aperture so the metering scale is in the centre for a proper exposure but it's longer than 30 secs where do you go from there?

Sorry if the question seems simple, I don't do long exposures and was wondering.

Regards

Phil

 

[woof woof]

In very low light I find that a cursor in the centre exposure leads to too bright an image. Other than that, as light levels vary so much, for me it's just quess work.

 

[Alastair]

As long as you need.

Something like this..



.. helps me find a starting point. Adapted from here.

With practice, you can guess a ballpark figure and chimp from there. Take a few high ISO and reduced shutterlength exposures if you want a rough guide before going to the full-length exposures.

 

[Phil Bennett]

Cheers guys

Phil

 

[gad-westy]

What I sometimes do is crank the iso right up (say 3200) and if it's really dark maybe open the aperture right up too. I'll fire some test shots until I'm happy with the exposure (either subjectively or from the histogram) and then start some furious head maths to work out how long I need to expose for my ideal iso and aperture.

So as an example:

Lets say I'm happy with a test shot at F2.8 and ISO 3200 with an exposure of 1 second.

The actual settings that I want are F8 and ISO 200 and if my maths are right I'd want a 2 minute exposure.

 

[Alastair]

f/2.8 and ISO 3200 at 1 second.. acoording to the table that's -2EV
f/8 and ISO 200, look-up -2EV and you get.. 2 minutes

Looks like we both agree

.. and I'll guess it's a moonlit landscape with the moon at or near full, or a scene lit with very dim artificial lighting.

 

[AshMashMash]

then start some furious head maths to work out how long I need to expose for my ideal iso and aperture.

I do the maths for every long exposure shot I do. Can't be waiting 4 minutes to find it's 1/3rd out or so. And it's really not difficult because you don't have to do very much maths... eg:

Filter ON: attempt exposures at wide apertures / high ISO. once you've got it, simply reduce ISO to 100 at multiply by ther factor (1600 >> 100, X16). Then even easier... going from F4.5 to F16 for example you click-click-click 3 times and double the exposure... if you're moving in 1/3rds for the aperture. Make sense? So if you're exposing for 1.5 seconds on a certain aperture, click 3 times and you're exposing for 3 seconds. Click along 3 more times and you're at 6 seconds...

Filter OFF: simply multiply by your filter factor. I use an ND110 - which is 10 stops, ie 1024X.

So 1/20 seconds filter OFF is 1000/20 seconds (50) filter ON. Simples.