8/7/2023 0 Comments AstroimagerThe software processing the data must thus be told the format of the colour filter matrix in order to ‘debayer’ the raw data to produce a colour image. This is a raw file format which saves a 16 bit word for each pixel but contains no colour information. Though these can be exported in the JPEG format, only 8 bits per colour will then be saved and in order to retain the full 16 bits of data per pixel, images must be saved using the FITS format. The EZcap capture software provided allows a sequential set of exposures to be taken which must be un-binned (1*1) to allow for colour capture. A desiccant tube is also supplied to attach to the camera to ensure that the air within the camera is dry so that no condensation can form on the sensor. The ‘square’ USB connector used at the rear of the camera is not very secure so that QHY now supply a 3D printed clamp to secure both the USB2 B connector and power cable at the rear of the camera. The 4*4 mode, which averages over 16 pixels, is significantly more sensitive and is used for rapid initial alignment on the selected object. The camera uses 16 bit digitisation and provides for 2*2 and 4*4 (monochrome only) binning modes. This makes the taking of dark frames at the same sensor temperature as the light frames far easier. (This is available from Modern Astronomy : ) The camera uses a 6 megapixel Sony sensor employing 7.8 micron square pixels and, most importantly, incorporates ‘set point cooling’ to cool the sensor to a specified temperature such as -20 Celcius. The lowest cost ‘One Shot Colour’ (OSC) camera currently on the market with an APSC sized sensor is the QHY QHY8L costing around £1,000 as shown below. Having perhaps been used to capturing images with a DSLR having an APSC sized sensor, one is unlikely to want a camera with a significantly smaller sensor. Many web discussions relate the relative merits of the two types but there is no doubt that a colour camera is simpler to use and will cost significantly less. CCD cameras can use monochrome or colour sensors, the latter having a Bayer matrix of red, green and blue filters above each set of four pixels so that colour images are immediately captured. A further advantage over an unmodified DSLR is that the sensitivity to the deep red H-alpha emission will be significantly greater. Images will thus contain far less noise and longer exposures are made possible as the greatly reduced dark current will not fill the pixel wells so quickly. Their great advantage lies in the word ‘cooled’ as, by reducing the sensor temperature to typically -20 Celcius, (and so perhaps 40 degrees below that of a DSLR sensor) the dark current made up of thermal electrons is reduced by a factor of more than 100 and its noise level by a factor of ~10. However, there may come a time when a beginner might consider a cooled CCD camera. Many of those who start out in astrophotography will use a DSLR camera. This is just one of many illustrated articles to be found in the author’s Astronomy Digest.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |