In the previous post we read about the equipment needed to photograph comet ISON. Now we will talk about the methods or settings we can use to picture the comet in particular. Let us have a checklist of objects.
· A Digital Camera
· Memory Card
· Battery/AC adapter
· Lens of your choice (in case of DSLR)
· Camera release cable
Digital Camera will capture the images digitally so we need to have several settings tested before we can actually go out and capture.
Exposure: it is the duration for which the camera collects the light and makes the image look bright. Every camera may be digital or film, has a shutter which blocks the light. Once the shutter is removed from the front (electronically or manually using the shutter button) the light reaches the sensor of unexposed film roll where the image is formed. A correct exposure will give the much needed details of the coma of the comet and the tails as well. A higher than required exposure will give details of the faint tail but the coma will be very bright and hence very little information can be taken out. Less than desired exposure will mean less information and hence the image will not have enough details on this.
ISO: The sensitivity measure of the sensor of the camera is called as ISO. It is increased logarithmically and is double the previous value of it. The sensitivity of the sensor means that every pixel on the sensor has some electronically controlled value of sensation which reacts once a photon (light particle) comes and falls on it. The energy of the photon striking a pixel is responsible for formation of image. ISO decides how sensitive is your sensor? Lower the ISO value higher will be the threshold value for each pixel and hence more photons or more light will be required to form the image. Higher the ISO value, lesser will be threshold value and hence less photons will be required to form the image. But due to the electronic circuit which have a lot of electronic components, prolong used generate artifacts due to internal heating of the sensor and hence grains in the image are visible. This is called NOISE and is different in different camera at different ISOs. So now you need to find that at what value of ISO your camera is generating how much noise. A little noise is welcome and accepted whereas higher amount of noise is not acceptable and it ruins the image.
Aperture: The amount of light entering through the lens can also be controlled through controlling the opening of the lens. This is called as aperture and usually is measured as ratio between total available and actual opening. Lesser the opening less light will enter through lens and hence the image will be dark. If the aperture is open maximum, then more light will enter and hence the image will be brighter.
Now since you have understood the three main parameters of camera handling, you need to identify what setting will be best for you to shoot this comet. The comet will be barely visible to you from a light polluted city so finding it in camera will be tough. You need a camera which can take long exposures. Now if you are not tracking the comet or compensating the rotation of earth then there will be a trail of stars or comet in the image. At 50mm focal length you cannot give exposure of more than 15 seconds which means you need to collect as much as 200 images for the same. The number of total images can be brought down to 50 images only in case you are at a dark location away from the light pollution of cities. So the rule of thumb says that you cannot exceed your exposure beyond 15 seconds so what else can you do to capture this comet? Remember, higher the focal length, less of exposure time will be possible without trailing the comet in the image.
One option is to increase the ISO. Since it would be winter season for northern hemisphere and early morning will have cold weather, you can increase the ISO to 1600. In normal course it will attract huge amount of noise, but due to cold weather, the noise will be low and you can get a brighter than normal image of ISON. Also you can take DARK FRAMES as much as 20% of the total images and then use it in processing to reduce the noise. The idea is to make the image as much noise free as possible so as to make the image look better and not ‘grainy’,
Aperture shall be open to maximum but one step down. So if you are using a camera lens say 50mm and maximum aperture is f1.8, you shall consider f2 or f2.2 as the right choice. This will improve the sharpness of the object without cutting down the quantity of the cutting light.
Focusing is very important in this case. As the comet will appear as hazy object in the sky, I would suggest that use any bright star and focus your camera. In manual cameras, use the focus to infinity as a nice and easy option. In digital cameras auto focus is provided but it is not a good idea to try auto focus. Point your camera towards the bright star say Sirius (visible around 2 am at good height) and focus it. Once you focus the camera, make sure you don’t change the focus for rest of the night. Now point your camera in east direction towards comet ISON (see older posts for the sky map to find exact position of comet ISON).
Make sure the memory card is empty and can hold at least 300 images in the night. Make sure the battery is charged completely. If the battery was charged few days back and haven’t used it since then still it will be a good idea to charge it again. A spare battery may come handy. Attach the remote timer or if using a laptop then please attach the cord. These days the smart phones are very smart and may allow you to control the camera using your android based smart phones. The apps are free to download and use. All you need is a connecting cable of your camera (mini USB mount) to the mount of your smart phones. These connectors are very easily available in the hardware market or on internet forums. This software also allows you to review the clicked image for better sharpness and focus reviewing. You can do remote shooting from your smart phones as well.
Now since you know all the basics, the challenge is to get everything together and start practicing and shooting. Luckily the comet has breached the 7th magnitude mark and is now within range of small telescopes and binoculars from a dark location. Photographing this comet has now become more easy and hence we shall try our hands on this comet.