ND Grad Filters

[Keith]

I have purchased some ND Grad Filters, Cokin to be precise and I would like some help regards exposure.

Is it better to take an exposure reading in spot or centre weighted evaluation of the mid to darker areas of the scene, i.e, landscape, then add the filter and use those settings, or is it better to take a reading of the whole scene using matrix evaluation (talking Nikon here) with the filter attached and then alter accordingly after taking test shots, or is it one of those trial and error scenarios where it is dependant on the scene and conditions in front of me?
Any help or thoughts or preferences will be appreciated.

[AlexB]

The ND grad will take off some light on the scene on the specified amount. Is better to take spot measures of both areas and apply the correct ND value to compensate for excess light.
best,
Alex

[Colin Southern]

The light that the camera meters has already been attenuated by the GND filter - so you don't need to compensate for the filter.

The metering mode that you use is your way of telling the camera which parts of the scene are important - for a landscape the whole scene is important, so matrix (Nikon) (or evaluative for Canon) is the correct mode.

However - automatic metering with high dynamic range scenes (as you've got) only ever gives you a starting point - from there you'll need to use EC (Exposure Compensation) to expose the scene correctly; the best way to do that is to have highlight alert and histogram turned on ... if you get "the blinkies" then you need to dial in -ve EC until they go away; if the histogram indicates a large degree of under-exposure then you'll need to dial in +EC.

Be aware that histograms and highlight alerts often don't consider individual channels - and often with sunrise/sunset landscape you'll have very warm colour temperatures - so you'll often need to under-expose the scene by a stop or more to avoid color shifts around the brightest areas.

[Keith]

Thankyou Colin and Alex, thats very helpful.

[eNo]

As an alternative for those cases where a GND filter can match the lines between dark and light, check out the VGND technique and see if you find it useful:

http://esfotoclix.com/blog1/?p=238.