John Cuff of Lee Filters was our speaker last meeting and our thanks to him for an entertaining and informative evening. Handmade Lee Filters are definitely at the higher end of the market but the money goes into precision raw materials and quality control. Now part of Panavision, probably best known to most of us as a credit for the lens makers on the closing credits of oh so many movies, Lee have been making filters for over 30 years. So this week I thought I would take the hint and we would look at camera sensors. No, only kidding, filters. Definitely filters.
Filters are essentially light modifiers, in that only certain wavelengths are allowed to meet the sensor or all wavelengths through darkening. We will come back to this shortly. Those of us long in the tooth who learned the basics of photography from film (not that you have to be that long in the tooth to have done that) will remember the 80A 80B and 80C or 3200K, 3400K and 3800K to daylight (5500K) colour correction filters. Then we had the 81 warming, 82 cooling and 85 tungsten to daylight series filters. Film, it should be remembered is a one off colour deal. There is no Auto White Balance on a film camera. There is a certain amount of dynamic range, but the colour balance is fixed. Colour filters with black and white effect how the greys are rendered, by and large. If you want to see the effect Google Picassa has a coloured filter on black and white option and it is free.
So, looking at the filters from the perspective of digital we are not looking at the colour balancing, that is done by the AWB or manual balance as we have already indicated. No need to pick the right coloured glass to screw on to your lens, you can dial in correction or you can let the camera do the work. Essentially we use the filters in a slightly more subtle way. Yes neutral density filters, polarisers and alike pre exist digital, but we are looking at the effects on digital and as light from the sun predates it by about 4.5 billion years and we have to take it as read, we are looking at the uses we can put these light manipulations to.
So let’s start with the Neutral Density filter, aka the ND, aka Stoppers. Simply put their job is reduce the amount of light reaching the sensor. Essentially we are manipulating the light before we start to process it through the camera via the Exposure Triangle. The uses of such a filter include effecting the depth of field when shooting with limited options of shutter speed, ISO and or aperture. Mainly it seems to be used for the slowing down of time to alter the relationship of something in continuous movement across or within a still frame. The much seen effect of milky flowing water or cloudscape comes from applying this sort of filter, it really is quite versatile when you have got your head around it. Graduated versions of the ND allow darkening parts of the frame that are very bright, such as sky lines, whilst allowing for the correct exposure of other section of the frame. With graduated filters the rate at which they darken, how hard the line is between unfiltered and filtered, varies and John showed us how sensor size has an effect on that and why Lee now have four designs to get the most out of the effect without making things too obvious.
The polariser is a popular filter with landscapers, but not exclusive to them, as they can increase colour saturation and decrease non metallic reflections. They are also significant because their effects, by and large, cannot be replicated in post. Their use also requires some forethought and getting the most out of them is a function of familiarity and practice. As with everything else that we use to modify the light its use and impact is best regulated to specific, desired effects. They work best when perpendicular to the sun and a popular way to work it out is known as the rule of thumb where you form a right angle with your thumb and index finger and point your thumb in the direction of the sun. The direction your index finger is pointing is optimal for the polarising effects, that is to say don’t have the sun directly in front or behind you. Of course the roles of index finger and thumb can be reversed but the principle remains the same.
Filters, then are about control. They can be used in subtle ways to control light variations in different parts of the an image or used to give a whole image effect. There are also effect filters to consider, such as those that give four or eight rays to a point of light (not currently made by Lee, I feel I should point out), or which render other distortions or patterns in an image. These can be replicated in post, of course, and these days their popularity seems to have waned. When Cokin first introduced their system filters into the UK nearly 40 years ago, the principle (only) medium was chemical/film based and it wasn’t unusual for a “Serious” photographer to be seen porting around half a dozen or more filters. Cokin changed the game with its system which was square when all the others on the market were round and its catalogue was famously 100 pages thick with examples of the filters in use and quite a work of art. They certainly shook the market up.
So our thanks to John Cuff and Lee filters for a very informative and enjoyable evening. Better start saving.