Sunday, 17 January 2016

How to capture rapidly, register and precisely crop, bridge camera images of the Sun or Moon

On January 15, A tripod mounted Panasonic Lumix DMC-FZ72 bridge camera at 60x optical zoom was used to image the 38% waxing, gibbous Moon. The camera was set to  ISO-100 and 1/250s exposure at f/5.9. 102 images, were precisely cropped and registered in Nicola Mackin's AstroCrop software, stacked and wavelet processed in Registax 5.1 with post processing in Photoshop:

38% waxing, gibbous Moon


The way that large numbers of images are captured in a short time is to use a static, robust tripod, and to hold the camera firmly whilst capturing the images. The camera is set to maximum optical zoom, with an appropriate shutter speed for the subject. the ISO is set to 100 to minimise noise and to set the camera to burst mode. The camera used here captures 3 images per burst, but other cameras may capture more. The Sun or Moon is kept as close to the centre of the field of view of the preview screen and focus lock is used so that the camera does not need to refocus for each burst capture. About 100 images are relatively easy to capture rapidly.
The images captured by the camera used here are 4608 x 3456 pixels in size, which means that even a small apparent movement of the subject between images, is in fact, a very large movement in terms of pixels. Too large, usually for Registax to be able to cope with the movement between images when it comes to stacking the images. What is required is to be able to precisely crop around the Sun or Moon in exactly the same way in every image, so that the cropped images can be presented to Registax with virtually no movement between images. This is a laborious task if done manually, which led Nicola Mackin and myself to develop AstroCrop software for registering and precisely cropping images. Nicola did all of the coding and I produced the required statistical algorithms.
In the Nov/Dec issue of Popular Astronomy, we published an article about AstroCrop:


The software can be downloaded from the website asys-software.co.uk The download website also has a short video showing AstroCrop in action with a small data-set showing extreme movement of the subject between images. There is also a PDF set of instructions on how to use the software.
Nicola Mackin, the programmer of the software was an IT professional for more than 25 years. She ran the European IT technical work for an International printing company. She now runs an independent publishing company aSys Publishing , publishing authors' work to the highest professional standards of the industry.
Nicola is also the programmer of the Aspect Ratio Corrector used to correct images captured by PAL video cameras.

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