The following are some of the practical aspects of choosing and using ND filters. This will hopefully be accompanied by a more in depth print article, but for now, here’s a summary!
What are they?
- Dark glass (or resin) which allow a photographer to lengthen the shutter speed.
- Screw on (circular) vs Square (slot in) – see below in accessories
- Light blocking terminology:
|Stops blocked||1 stop||2 stop||3 stop||10 stop|
|No filter = 1 sec||2sec||4sec||8sec||1024sec|
- Tripod : MUST be firm and steady
- Cable release : essential to achieve exposures of greater than 30 seconds. Some firmware changes such as ‘magic lantern’ and some camera applications (such as for the sony A7r series) offer an alternative to a cable release but I prefer the former.
- Filter holder and square filter set up. Allows 2(Lee default) to 3(Nisi default) filters to be stacked in front of the camera. Lee requires an additional slot for a 105mm CPL, Nisi system has a CPL attached to the default sized adaptor ring itself. Insert ND filter on the closest filter slot with padding firm against edges of the holder to prevent light leak.
- Screw on filters need no filter kit. Minimises light leak but unable to ‘stack’ with other filters. Can be used with CPL but could lead to vignetting.
- Optical view finder cover (to prevent more light leak). Can be on the camera strap itself (canon) or can be anything invented ! eg. Blue-tac, duct tape.
Density recommendations (approximate)
- 2-3 stop : for waterfalls, seascapes in bright light : target shutter 0.5-5 seconds
- 6 stop : for fast moving clouds, seascapes in low light: target shutter 5-60-seconds
- 10 stop: for elimination of water textures, slowish clouds: target shutter 1-5 minutes
- 15 stop: same target as 10 stop except in brighter conditions: target shutter 1-20 minutes
- Vari-ND: limited by screw on setup and some brands have bad cross polarisation artefact.
Camera setup :
- Turn off long exposure noise reduction. (noise reduce in post processing)
- Turn off autofocus . Leaving it on may result in the camera hunting in the dark for and lead to an out of focus image
- Keep iso low. This is within camera limitations. I like to keep iso <400. (if going much higher, could you just achieve the same results with camera settings alone or less dense ND filter?)
- Activate expanded iso (eg. Iso50 for canon users)
- Adjust aperture according to given scene. At your lens’s sweet spot at f8, the exposure may not be long enough after minimising iso and placing your densest ND filter.
- Usual rules of composition apply
- ND filters allow simplification of ‘chaotic’ elements eg random water motion, unattractive clouds. Use these to emphasise areas of detail within your image
- Compose without ND filter on to achieve your desired composition and to find your focal point manually.
- Don’t let the ND filter dictate the shutter speed. Use ND filters to achieve the shutter speed you desire for the scene.
- For every stop of light blocked, exposure duration doubles. (See first table)
- Use apps if you don’t mind bringing devices into the field
- Alternatively, use this approach outlined in this link: https://everlookphotography.wordpress.com/2016/05/24/quick-tips-live-view-simulation-and-long-exposures/
How long do I want?
- See the above section in ‘density recommendations’
- Start with that filter and adjust iso/aperture accordingly to achieve the exact shutter that you need for the scene.
- During your test exposures without the ND filters, take some dedicated shots with shorter shutter. You might like them more!
With or without filters?
- Think about combining filters to achieve a single exposure result
- Using an additional GND for the sky
- Avoid stacking ND filters as the filter in the 2nd slot will almost certainly let light leak in
- Think about taking an image for dark areas of the scene without the ND filter on as the ND filter will require a very long exposure for deeply shadowed areas. Blend them in post processing.
Ultimately, repetition leads to reflexes and if the routine is a reflex, more thought can go into the art of achieving a result instead of the mathematical and technical processes of using filters. Enjoy!
Disclosure: I am a Nisi brand ambassador who tries to write neutrally and objectively. If you are interested in purchasing filters after reading this article, feel free to email us dm@everlookphotography and I will be able to give a discount code for Australian customers.
Marianne and I took a mini-break to Normanville in midwinter to give our second child her first taste of a short holiday. The weather forecast for that weekend was pretty terrible with rain , strong wind and rough seas forecast. On the first evening , second valley jetty looked as though it was being swallowed up by the sea at times with bursts of water coming through the planks. There were also winds gusting up to 80km/h , and intermittent rain which made it a truly wild scene. The challenge was to come back with any kind of usable image. My plan was to position myself to be able to record the action while being relatively safe. Because I knew water would be splattering the lens in every frame, I really only planned on setting up for one composition for the entire evening and firing different exposures for lighting and wave action while wiping in between (usually I am much more mobile on a sunset shoot exploring compositions for the possibility of changing light) . Very long exposures were out of the question and I found that the wind would be blowing me and the tripod of our spot from time to time anyway! The camera was covered in a rain jacket and I was covered in my goretex outers. I came back with a bunch of exposures I couldn’t view in real time and thoroughly soaked from the experience. The image below is one put together from different aspects of the evening and despite the number of shots fired, there were still some smudged aspects of the image!
Hope you enjoyed this quick discussion 🙂