Thursday, June 18, 2009

Graduated Neutral Density filters part 1

Let me start with a disclaimer. This post describes my experiences. I am by no means an expert, I’m just writing this to order my own thoughts, for the fun of it and for the slight chance that people with even less knowledge than I have may find it useful.

All example pics are clickable and will lead to flickr where you’ll find different sizes and full exif.

A recent article in Amateur Photographer got me interested in using neutral density filters in my landscape photography. Landscape shots can be demanding because you’re often dealing with a lot of dynamic range. A typical landscape shot can end up like this.

Shot in matrix metering. 3/4 of the picture is sky so the camera tries to expose the whole scene properly but ends up with a sky that’s more or less acceptable and a ground that’s just too dark.

I must add here that my Nikon D300 outperforms the s*** out of my old D50. With the D50 the ground would have been much darker and lost detail.

Anyway, enter the gradual neutral density filter.

What is it?

It’s a filter where one part is colored and the other part isn’t. They exist in two main types, screw-in and rectangular in a holder. I’ve looked at the screw-in type and consider it less than ideal. It’s not flexible, you’re depended on what the manufacturer has decided for you.

Instead I went for a system with rectangular filters. Because I’m on a limited budget and because of availability I went for Cokin. Cokin is a well known French filter maker that many of us remember from the film days. They’re not dead yet even though I don’t really see a use for many of their products any more.

Cokin makes filters in 4 sizes. For us hobby photographers on a limited budget only the smallest two are of interest. A-system which will fit lenses up to 62mm. I went for the P-system which will fit lenses up to 82mm. P-system is a bit more expensive but because the filters are bigger (84mm wide instead of 67mm) there’s more room to move them and some of the lenses that are on my someday list have a 67mm thread.

Cokin sells single filters but also kits. I selected the H-250 kit  which includes:

  • Gradual Grey G2 (ND2)
  • Gradual Grey G2 (ND4)
  • Gradual Grey G2 Soft (ND8)
  • P-system holder

Now for the holder to mount on the filter thread on the front of your lens you need an adapter ring. They are relatively cheap and available in loads of sizes. I selected 52mm for my 50mm and 18-55 zoom and 62mm for my 28-105mm zoom. I bought all this mail order from Foto Konijnenberg. Ordered and paid on Monday, received it yesterday.


I also ordered the P255 stackable hood, more on that in a future post.

Using it

Open all the packages, slide the appropriate ring in the holder, screw it on your lens and you’re ready to go.

It’s not quite that simple of course. I started by digging up the old Velbon tripod I have on long-term loan from my dad. Went to a nice spot just outside town and set up. I metered in spot metering off the ground of the image and then set the camera on the tripod. To establish a baseline I first took the shot in matrix metering:

Like I said, results like you would expect. I then slid in the first filter, the 121L which should help cover a two stop difference between the sky and the ground.

It took me some fiddling to get it properly positioned. Fortunately I remember something I read here where they advise you to use the DoF preview button to check the placement of the filter. That does help.

I then tried the 121S which is a whopping 8 stops but with a softer transition between the colored and the blank part.

So… it does work. What I have learned already is that your metering requires real attention when you’re doing this. You do need to know rather exactly the difference in stops between the ground and the sky. That’s a matter of shooting discipline.

What I need to learn and to gain some experience in is positioning the filter properly and quickly and shooting without tripod. Yes, I know  I shouldn’t but the main reason I bought this kit now is our family vacation to Cornwall and Devon this summer and I can’t have the rest of the family waiting around for minutes while I set up for a single shot.

There you have it, my first small steps in filter usage and yet another step in learning proper landscape photography.

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