Week 8: Longer Exposures part 2…
In class this week we stayed on the topic of long exposures and filters.
ND filters come in varying levels of opacity that tie-in to F-stops. To recap, when changing the F-stop, with every 3 clicks you either double or halve the exposure (amount of light that is let into the sensor).
Similarly, ND gradients double with each step up (or halve with each step down). So:
ND2 = 1 F-stop
ND4 = 2 F-stops
ND8 – 3 F-stops
ND 16 = 4 F-stops.
So if your long exposure results in an image that is overexposed by 1 F-stop, you can combat that by using an ND2 filter setting, etc. etc.
Really dark ND filters can leave an X-mark in the middle of shots. Check reviews at sites such Digital Photography Review; buy online at Amazon or Wex Photographic. Apparently, Hama Filters are a reliable brand, with filters between £37 and £65. Hama, if by any chance you’re reading this, I will be happy to put this claim to the test.
Aside from variable filters, you can buy filters for each individual ND setting (both screw on and slide filters) and graded slide filters – which allow you to have a sliding scale of exposure on an individual image.
Polarised filters are used to get rid of reflections/glare (usually on non-metallic surfaces such as glass) and increase clarity. They can also be used to achieve a deeper blue when shooting sky (if taking the shot at a 90-degree angle from the sun) and also to deepen colours by reducing extreme highlights.
You can stack filters and combine them, but there is a risk of vignette effect when shooting on wide angle. The best way to check for this – although by no means perfect – is to use the live view monitor, as this depicts more of the actual shot than the viewfinder (which only shows around 90% of the end shot).
This week’s homework was to practice using an ND filter and Polarised filter. Unfortunately, I was still sick as a pig, so didn’t get round to buying either or shooting much at all. Instead, I took a few more shots last night, in a little pedestrian byway in Sheen called Model Cottages. Would have taken more but for some odd bloke who was hanging around and acting mighty strange. Figured I’d best move on to somewhere a bit busier, so ended up taking some shots of the flats on the corner of my road. Not sure why. Think I liked the strong lines. The last shot is what happens when you fail to tighten up the tripod properly and halfway through a 30-second exposure your camera starts slowly heading South. I have to say, I kinda like it. I may have invented a new thing.
New thing aside, all in all a most unproductive and underwhelming week as far as practice goes but at least I did get the camera out once.