Nick Miners Photography

Thursday, November 5th, 2009

It’s a little late in com­ing, but I did prom­ise a les­son in how to use gradu­ated fil­ters. It fol­lows on nicely from what I spoke about in my post about the Zone Sys­tem, so please famil­i­ar­ise your­self with that one before read­ing this if you haven’t already; this one will make more sense that way.

I men­tioned that the range of bright­ness that a cam­era can ‘see’ is much nar­rower than that of the human eye. In most cases, you can isol­ate an inter­est­ing part of an image and bring out the detail where it’s rel­ev­ant, how­ever there are many situ­ations where this simply doesn’t work. For example, if you are tak­ing a land­scape pho­to­graph that includes a lot of sky, espe­cially late in the day, the fore­ground will gen­er­ally be three or four stops darker than the sky. By meter­ing for the fore­ground, the sky will be blown out, but if you stop down to increase detail in the sky, the fore­ground will usu­ally become too dark.

Of course, with RAW files and soph­ist­ic­ated post-​​processing tools such as Adobe’s Pho­toshop Light­room, it can be easy to fix such pho­to­graphs after­wards, but this won’t always work, as often the sky is so over­ex­posed that the high­lights end up edged with grey as col­our detail is lost. HDR is another option, but is time con­sum­ing, and the effect is not to everyone’s taste (myself included). It is far prefer­able, I believe, to achieve the effect you want in-​​camera. So how do you do this?

Take the fol­low­ing pic­ture of the church at Prest­bakki in north­ern Ice­land as an example:

There is some great detail in the fore­ground, with the gravel and the weeds among the flag­stones clearly dis­cern­ible, but the sky is almost pure white. I could stop down by 2 stops to bring the clouds into detail, but then we lose the inter­est­ing tex­tures on the ground:

How­ever, by apply­ing a 2 stop neut­ral dens­ity gradu­ated fil­ter (usu­ally referred to as an ND grad) with the dark half placed so that it cov­ers the sky, I can keep strong detail in both halves of the picture:

This is a par­tic­u­larly strong set­ting, mainly for illus­tra­tion. The best use of ND grads is when you can’t tell it’s been used. Com­pare the next two pho­tos of the river Lagan in Belfast:

The first was taken as is, and for the second I used an ND grad to drop the sky down 2 stops so that it was the same bright­ness as the river. The con­trast between reflect­ive sur­faces (such as water) and sky will always be less than that between, say, grass and sky, so it’s pos­sible to make the whole pic­ture appear more uni­form. This is another com­mon use for ND grads where you won’t neces­sar­ily get the same loss of detail caused by excess­ive dif­fer­ences in brightness.

Finally, an example of where an ND grad really comes into its own:

This was taken at Thirlmere reser­voir in the Lake Dis­trict. The sky was turn­ing some beau­ti­ful col­ours, but the bracken was a lovely shade of orange/​brown and the dry­stone wall provided a nice way to draw the eye into the pic­ture, so I placed my usual 2-​​stop ND grad on so that I was able to cap­ture the lot.

Note that there are many types of ND grad fil­ters. They vary from 1– to 4– stops, and in the degree of grad­a­tion, with a hard edge for clearly defined hori­zons, and softer edges for when fore­ground detail (e.g. trees, tall build­ings) intrude on the sky and would be spoiled by excess­ive dark­en­ing. It’s a good idea to have more than one to hand, but you can vary the soften­ing effect by using the aper­ture. A nar­rower aper­ture (higher ‘f’ num­ber) will harden the bound­ary between dark and light halves, so open up as wide as you can if you want a softer edge without chan­ging fil­ters. You can also buy screw-​​on ND grads which rotate inde­pend­ently of the lens, but you can’t move the hori­zon up or down with these, so it’s bet­ter to get the rect­an­gu­lar acet­ate fil­ters in the Cokin or Lee series.

I hope this les­son has also been help­ful. Please use the com­ments below to let me know if I’m strik­ing the right tone. I’d also like to see any pho­tos you take using ND grads; you can link to flickr if you have any you’d like to share.

Tags: Adobe, Belfast, exposure, filters, graduated, Iceland, Lake District, landscapes, Lightroom, sunset, technique, Thirlmere, zone system