Wednesday, 4 August 2010

How to Use a 10 stop ND filter

One of the most common questions you get as a landscape photographer is "What filters do you use?",  second only to the "did you do a lot of Photoshopping on this picture?".

Well normally I only use ND graduated filters to hold back the brightness of the sky.  Without them you either get white sky or black land under the more extreme lighting conditions of sunset & sunrise (alternativly you can use HDR).

Lately I have been messing around with a 10 stop B&W filter.  The main reason for using it is to get a much longer exposure,  which can lead to movement in the sky or to smooth out waves in water. In addition any people (or in this case ducks) that  are moving disappear out of the photo.  Here is an example of the effect, taken on the banks of Derwent Water:


Kettlewell
181 Seconds at f/22 Using a 10stop ND filter.

The 10 stop filter is a very dark piece of glass - like shooting through a welding mask.  So it requires a slightly different technique.
  • First I set up the camera on a sturdy tripod.  I set the camera to in manual mode and took a straight shot at f/22. 
  • A look at the histogram confirmed a 0.3nd grad would be needed to calm down the sky and consequently lighten the land.
  • Another shot confirmed that the 0.3 filter was correct.
  • Next I switched the lens to manual focusing as auto focusing through the 10 stopper dosn't always work and our test shots have confirmed the focus & composition are what we want so we don't want them to change.
  • Screw the 10 stop ND back on and then the 0.3ND.
  • Using the ND Calc iphone app allows me to easily calculate how much the exposure is lengthened by adding the 10 stopper. 
  • I Switch to bulb mode and then use the timer built into ND calc to time the exposure. 
  • Then just open the shutter till the timer goes off and try not to get bitten by too many mossies.

Just so you can appreciate the effect of the filter. Here is the test shot:


1/6Sec @ f/22

You can achieve similar effects without the filter.  But to do that  you need quite low light, this was taken 45 mins before sunrise and it was so dark that to the naked eye you could hardly see the pier:

 Southwold Blues
15 Seconds @ f/5

3 comments:

Dave Peck said...

Thanks for that iphone app link. Really useful.

sumit031 said...

thanx for the info, with example....was really usefull!!

lawrence40 said...

I've a 10 stop nd filter on order and can't wait to get trying it out. meantime I've doing a little research and found your post. thanks for the information, also love your images