It depends on the time of the day, and ambient lighting in general, whether it is changing significantly enough. I’ve had situations where i’ve metered and calculated the 2 exposures and just gone ahead and done it with no problems. But then sometimes (often in the evening, when light levels are changing rapidly), the light can change enough with the long exposures, that sometimes by the second exposure, your previously calculated reading is already a full stop or two out. I must confess sometimes i carry a hand held light meter which shows me the EV readings which i can keep track of. But as a general rule, not so much during the day, but at the end (or start) of the day, yes you should re-meter.

Another way to quickly ‘re-meter’ is to take a test shot without taking filter off and wasting time and bumping your camera’s position, change up your ISO to an extremely high value and shorten your shutter speed down by the same no. of stops, check histogram, make adjustment and go back to low ISOs for another long exposure.

Andy

For a photographer of more limited means (I don’t have a second camera to use exclusively for metering!), would you recommend I meter both the sky and the water before composing my shot for multiple exposures? Depending on the length of the first exposure, do you think this would be sufficient or do I really need to take a fresh meter reading?

I guess I need to experiment.

Thanks Andy!

There are several ways you can do it. But basically i meter the scene with no filter, work out what shutter speed i need, then multiply it by 400 (for ND400) to find the exposure i need. For example if i meter and find out i need 1/400th with no filter, then this means i can shoot 1/400 * 400 = 1 second with the ND400. Or say i meter 1/8s, then with the ND400 this means 1/8*400 = 50 seconds. I carry a cheat sheet i made myself which basically has a table of these calculations for different NDs.

You can do this by taking the filter on and off the lens, you have to do this when it gets dark, i.e when exposures are over 1min, since otherwise it is too dark to compose or see anything through the viewfinder or even live view. But when its brighter i can see okay, i use a 2nd camera to do the metering for me, this way i don’t need to keep unmount/remounting the filter.

Regards,
Andy

Thanks for this blog – I for one think it’s very useful and informative.

Question about longer exposures for you. I understand the need to time the exposure when in bulb mode, and this is probably a question that cannot really be answered…but how does one know how long to expose for? Trial and error? A formula based on light metering?

I’m always impressed when photographers tell me “so I opened it up for a 100 second exposure and …”, but then I wonder how on earth they knew it had to be 100 seconds (or any other figure).

Cheers,
David.