Recently I have been trying to use my Graduated Neutral Density (ND Grad) filters more to compensate for bright skies and relatively darker foregrounds. I have found, as is common, that being relatively affordable filters, they do tend to result in a bit of a colour cast, sort of blue/purple depending on how intense the filter and how btright the light is. So, since I have two sets of ND Grad filters (Cokin P series and Formatt Hitech) that I would try a little experiment.
I set up my Canon EOS 5D Mark II with its EF 24-105mm f/4 L lens on the tripod outside the house, looking towards Sgurr Mor. Not a particularly special compostion but it was lit well from the south-west. I then set the aperture and shutter speed in anual mode according to what the camera meter decided was the proper exposure, 1/50 sec at f/11, ISO 100. Without changing the exposurte I took a photo at the same settings using the various filters. I then repeated the exercise (for the soft grad filters at least) but adjusted the settings for each shot according to what the camera dictated as proper exposure. The results can be seen below and you will see that the filters basically darken down the sky, emphasising the blue and the detail of the clouds. However, at the higher filter intensities there does begin to be a bit of a cast. Also, the ones taken with metering done with the filter in place prvode a better balanced shot I think as you might expect. I think there is little difference between the different types of filter until you get to the more intense and then I feel the Formatt introduces more of a blue/purple cast.
It probably doesn't matter too much as this can be corrected in Lightroom by adjusting the image temperature but the experiment does suggest that often less is more, i.e. using less intense filers works best. In a compostion with a brighter, blown-out aky a heavier filter would no doubt work better and almost definitely be necessary to retain any detail int eh sky anyway.
I am an amateur photographer who is also a Chartered Geographer (GIS) with his own part-time consultancy business and I work as an estate manager for a national conservation charity in Scotland. I am based in Lochalsh, Wester Ross, Scotland, just next to the Isle of Skye.
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