RocketSTEM Issue #7 - May 2014 | Page 21

highest ISO setting on the camera. You can use a lower ISO setting to reduce the noise in the image, but you will also lower the sensitivity and the number of stars that can be recorded. Focusing can be a little problematic as the lens is to take images through a telescope. This is where the is at the end of the focus movement . You need to set the focusing mode into manual focus and turn off any camera mounting to a generic lens. This is known as a T2 mount and has the bayonet on one side with a thread inside. The thread is used to screw in an eyepiece adapter resulting in a sturdy during the day on something as far away as possible helps me get set up. A piece of electrical tape is your friend here as it can be placed over the focus ring and prevent movement. When night falls and you set up to take your pictures there should only be a small amount focus. fore. Why not replace the lens with a telescope? The mechanics of this is surprisingly easy. The camera lens Computerised Camera Control If you want to get a bit more serious about astrophotography and have a laptop and compatible camera you can shoot in tethered mode. This is where the computer controls the features of the camera. Canon cameras are particularly useful for this as there is a lot of software available, both Commercial and Freeware, that can control the entire imaging process. I still have my D300, but I decided to get a dedicated astrophotography camera, and after a lot of comparisons decided to go for the Canon T3i a versatile workhorse that could be fully controlled by my computer. I also use APT - Astro Photography Tool a Freeware imaging application. APT does far more than just control the camera, but this is the area that I am covering here. For more details about APT check their website at www.ideiki.com. Just above I mentioned the problems with focusing at night. APT is able to control the camera lens and can ever do manually. It also has a number of features that assist in achieving focus including live view, lens control, autofocusing, and focus aid. Using these tools help you frame and focus your image. APT also has a feature that allows you to program a sequence of shots enabling you to automate the process of your night work. I have just touched on the surface of what the program can do and there are many other alternatives out there that do the same thing. As each camera offers different facilities check with the compatibility purchase or acquisition. Connecting to a Telescope alone camera, but a main concept of astrophotography www.RocketSTEM .org The bayonet and nosepiece of a T2 camera mount adapter. Credit: Mike Barrett connection between the camera and the telescope. The telescope then becomes a long focal length lens. There are a couple of drawbacks to using this method for connecting a camera to a telescope. The main problems are backfocus and star trailing. Backfocus in astrophotography is the ability of the on the body indicating where the sensor is. This is also the focus point of the camera. An eyepiece has it’s focal point some way below the eye, but a camera has it above the plane where your eye would be. This means that the telescope focuser has to be able to move in far enough for the camera to achieve focus. This is normally not a problem with a refractor telescope by using a Barlow lens which shifts the focus point and can allow the camera to achieve focus. 19 18