Let us find out the significance of dark frames by studying the topics below. We are going to cover the following
Lets answer the questions one by one.
What is a dark frame ?
Long exposure photography causes noise in the pictures. Especially while shooting star trails. In Star trail Photography there are multiple long exposure images which eventually will be stacked upon each other to create one composite image. To tackle the noise issue, Digital cameras have a ‘long exposure noise reduction’ on/off option in the settings.
When you choose long exposure noise reduction to be ‘On’ it takes more than a normal time to write the image on the card. That’s because the camera is creating a dark frame itself along with your long exposure photograph. This dark frame is created to reduce noise caused by long exposures.
With low light or
where the exposures are long, the ISO tends to be on higher sides, hence more noise is produced. Dark frames are nothing but a completely dark frame which helps reduce noise when stacked upon your image.
How to create dark frames ?
You just have to take the same exposure with the same settings as that of your intended long exposure photograph but with the lens cap on. Yes, that is the dark frame. How does it look? Have a look at the below picture.
shooting, it is recommended to shoot at least 10-15 dark frames per 100 exposures. Since your long exposure noise reduction will be turned ‘OFF’ to achieve faster writing speeds on the card, the camera is not going to produce any dark frames on its own. Therefore you have to shoot dark frames manually to tackle noise in your images.
Apart from helping to reduce noise, dark frames also help to eliminate hot pixels from the images resulting in good quality outputs.
How to use dark frames ?
Software programmes like Starstax or startrails.de have an option to feed dark images to them directly. You just have to include your dark images with all your images and go with the stacking. Starstax has a programme to create and include dark frames at a click of a button. Same with Adobe Photoshop.
With Photoshop, since it is a manual process, you can place dark images selectively and blend them with your exposures the way you want it.