Question about stong ND's

[Ran_photography]

With ND's, like 10 stops, for extremely long exposures, when you turn it to bulb, how do you know how long you wait for the exposure to go?

[eddarr]

Start with an exposure that the camera can figure out for you. If it says 2 second exposure then you add the ND increase by 10 stops and use a stop watch or something with a second hand. Often times you may have to adjust it a little based on the histogram. Expect to take 2 or 3 shots to get it dialed in.

[blackcap]

A 10 stop filter lets in 1000 times less light, so work out your exposure without the filter, then multiply by 1000. So if the shutter speed is normally 1/200, set it to 5 seconds with filter on. 1/30 becomes 33 seconds and so on.