The Black card technique is done using a card (doesn’t actually have to be black – could even use an envelope or thick piece of paper) to reduce the exposure of part of the exposure. Generally it’s best to use it with a flat horizon in the same manner as a hard graduated filter.
The technique is used if the dynamic range is too great between components of the image that results in unrecoverable highlights or shadows.
The principal is to hold and gently vibrate the black card over the brighter area to reduce the exposure. The card is removed so that the brighter area has a satisfactory exposure. The card is vibrated to avoid having a hard black edge to the card being evident in the image. For example – a 30s exposure – to reduce sky by 1 stop would mean you would remove after 15s (to have a sky with 15s remaining), 2 stops after about 12s (to have about 8s remaining and 3 stops after about 26s (to have about 4s remaining) as stops work on a doubling of the exposure.
Advantages vs a hard graduated filter
- It’s cheap – can vary the exposure to whatever is required with the one black card whereas with a graduated filter you would need to either have one for each exposure difference or stack them. If you consider the cost of high quality filters such as Lee filters, then this can be quite expensive.
- Image quality – there is nothing in front of the lens to reduce quality. Some filters are really cheap and can reduce image quality. Filters can also start causing colour casting that may require fixing. Also – filters may damage over time (scratches) that further reduce the image quality.
- Mixing exposures – this is a plus and a minus depending on the effect that you want. The sky exposure will be reduced so if you want less motion in the clouds but still want long exposure water.
Advantages of a hard graduated filter
- Can be used for shorter exposures. Black carding only really works if you’re using a long exposure. I’ve used a short exposure of <1s successfully before, but it’s much more hit and miss as to the result. So therefore most of your time maybe involved in the technique rather than capturing the image.
- Easy – you see immediately what you want out of the reduction of light.
Other black card limitations
- Doesn’t work very well in a windy environment
- Preferred to use on a flat horizon – otherwise you have the same limitations as a hard graduated filter. If you’re really enthusiastic, you can use the card on controlled areas of the scene, even cut out the horizon shapes.
Below is a video I made to demonstrate the technique.
Here are the test shots from the video. I’ve done a uniform colour balance and reduction of exposure (-1 in LR) on all 3 images. My apologies about the quality of the images, conditions were rather average and only wanted to show the test.
20s exposure with no modifiers (no GND or black card) – the sky is very over exposed –
20s exposure using black card for about 17s to represent 3 stops – you can see less cloud movement –
20s exposure with a 3 stop hard graduated filter – you can see that with the fast moving clouds are more blurred –
Exposure of <1s. This isn’t recommended because you can’t be precise with the exposure and there is a reasonable chance that the card will be captured partway in the image for a completely dark section.
I’ve also used it in conjunction with the Lee 10 stop big stopper before. This works well for me as it improves the range of exposures.
Astrophotography – gets a bit harder. I’ve done a 60s exposure with black carding – so a 30s sky exposure and 60s on the entire exposure to bring out the foreground more. It’s not easy because it’s dark so you can’t place the horizon very well. You can possibly use a torch to light the foreground to assist working where to hold the card initially.
Fireworks – black card can be used to wholly cover the lens during fireworks and then removing when appropriate to capture them.
Other alternatives include software alternatives like exposure blending, HDR, luminosity masks.