Bulb exposure timing

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johnl69

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John
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How do you work out what shutter speed is required when using ND filters in bulb mode?

Ive just been taking random exposure at different time but there has to be a better and quicker way.
 
Think you may have phrased your question wrongly.

In bulb mode the shutter stays open as long as you keep it open.

Do you mean how long do you keep it open?
 
johnl69 said:
I mean how do I work out how long to keep the shutter open for
Click to expand...

Expose for the shot with out the filter. Then multiply the shtetr speed by the filter factor.

EG: filter with a filter factor of 64, shuteer speed of 1/60. When filter is placed in front of lens you would require a 1 second exposure.
 
Thanks for that so am I right n thinking that the filter factor is the filter number i.e ND8 has a filter factor of 8?
 
I'm confused... filter factor 64? Sounds like suncream...

Just double the length of the exposure for every full stop of filter. Lee/Hitech ND 0.3 is 1 stop, 0.9 is 3 stop, etc. Not sure about the Cokin ND8 scale, but it's certainly not 8 full stops.
 
There are different ways of expressing filter factors, but ND8 is three stops. x2=1, x4=2, x8=3, x16=4 etc.
 
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