The first set of images were taken to test out the use of ND Grad filters. In fact I have been using these filters for about 18 months now and they are excellent for reducing contrast in order to retain either shadow or highlight detail. I have not however made a systematic comparison of using these filters with different lenses and f stops.
The first three images compare a scene at Famara Beach in Lanzarote - the sky was overcast with cloud detail visible . Image one is wide open no filter, the second is wide open using a 0.6 Graduated filter and the third is stopped down with the filter.
Using the filter clearly brings out the detail of the cloud formations, but it also in this case reduces the overall contrast. With a cloudy sky this has resulted in a very flat image using the filter. In this situation there are clearly pros and cons of using a filter as the contrast range was workable without the filter - something to think about when on location - I have noticed that the contrast range of some of my shots when using filters has been very compressed.
I looked at a detail of these images to find out if stopping down made the edge of the graduated filter more visible with the greater depth of field created by stopping down. These are the comparisons. Wide open is the first and stopped down is the second...
Frankly I can see no difference in these two and I have been told that this is most likely to be the case if one uses high quality filters. My filters are Lee Filters which have the reputation of being the best around....good idea to buy the best filters it seems.
I also made some comparisons in different light conditions. These shots were taken at Famara in Lanzarote - this time looking inland towards the mountains and an old building. A large part of the sky was very featureless. The first image is without a filter and the second is with.
In this case the filter has revealed some texture in the clouds which works well but once again the contrast is lowered and I am not sure I like this.
The next two shots were taken into a sunset with some blue sky and cumulus clouds. Again the shot without the filter is presented first.
In this situation with a much higher contrast ratio between sky and land the filter has worked really well. The sky is well exposed and shadow detail is still visible in the foreground wall and beach - the lesson from this seems to be that I need to establish what the contrast ratio is first and then decide when to use a filter...previsualisation seems to be the key. When in doubt I might also shoot with and without a filter to create options for later processing.
The final test I made was to see whether the ND Grads worked as well with a medium telephoto. These two images show a comparison taken with a lens of 90mm (35mm equivalent). The first without a filter and the second without.
I could not see any deterioration in performance with the longer lens and the filter has worked well in this situation to hold back the sky and reveal shadow detail in the wall in the foreground.
So the key lessons for using Graduated ND filters are to use high quality filters, in overcast conditions to consider what is more important - highlight detail or higher contrast, to bracket exposures when not sure to provide options in post processing.
I will post my findings on polarising filters in a separate post in the next few days.
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