Using a polarising filter (35)

Requirement

x images

Purpose

To understand the role of the polarising filter and how to use it to greatest effect

Technical learning

 

How polarising works

• Polarising light typically darkens clear sky, improves the tonal quality of foliage and makes water surfaces more transparent.
• Unpolarised light vibrates in all directions in a plane at right angles to its direction of travel. When light is reflected from a non-metallic surface, it will be partially polarised, i.e. the wavelengths will be more constrained to one direction in the plane at right angles to the direction of travel
• The Polariser does its work by removing glare and so enhancing colour saturation and contrast,  i.e. it screens out light which is not vibrating in a single direction. 
• The effect works best when the camera is at right angles to the sun and requires rotation to fine tune the polarising effect

Ancillary effects to note

• Polarisers reduce the level of light entering the camera between 1/3rd and 3 stops (depending on the strength of filtration). Consequently, shutter speeds will be slower unless adjusted by dialling up the ISO setting. 
• Polarisers work most evenly with standard or moderate telephoto lenses. The breadth of the wide angle lens results in uneven distribution of the effect of reducing glare.

Exercise instructions

Part 1 - Skyscape

Set-up

• Pick a clear or partially clear sunny day
• Work when the sun is relatively low in the sky (e.g. mid morning or mid afternoon in spring or autumn)
• Select a viewpoint with a 360 degree aspect
• Use a tripod, standard or moderate telephoto lens and a polarising filter
• Frame a view that is at 90 degrees to the sun with a significant part of clear sky
• Rotate the filter to establish the lightest and darkest treatment of the sky

Images - standard or moderate telephoto

• Shoot the brightest and darkest compositions 
• Re-compose image so that the sun is directly behind the camera and shoot

Images - wide angle lens

• Shoot at the darkest setting

Review

• Examine impact between brightest and darkest rendering of the sky using the standard/ moderate telephoto
• Compare the darkest (standard/ moderate telephoto) with the darkest (wide angle): is the first more even than the second?

Part 1 - Water scene

Set up

• Pick a relatively bright day
• Select a scene with water  (e.g. a river, lake, etc) with items immediately below the water line (e.g. rocks)
• Aim the camera at the water at the same angle at which the sun strikes the water  (e.g. 30 to 40 degrees) 
• Rotate the filter so as to maximise and then minimise the reflections seen through the viewfinder

Images

• Take a pair of polarised and unpolarised images of the water

Images and review

Waterscape -  Virginia Water

 

Polarised - rocks beneath water become clearer

Unpolarised

 

Skyscape - Beach at Burnham-on-Sea at low tide

 

Polarised
Stronger definition of clouds, more intense
blues

 

Unpolarised