Creating the Image Processing File

You have finished your image session and you have brought the valuable sub-exposure data indoors to be processed into a wondrous deep-sky image. There are a number of hurdles to be overcome before we end up with a pretty picture. The first thing to do is to convert your individual FITS sub-exposures into IEEE floating point format using Maxim DL's Batch Save and Convert routine. This step is not entirely necessary if you do not have the software to carry out the conversion. You now need to...

Reflector Refractor Imaging Combination

Unusually for this hobby there is actually a win-win combination you might like to consider, provided your finances will allow it. You can have the large aperture reflector as your main imaging telescope at the larger f-numbers, typically your scope's native f-number will be around f 10 and this can be reduced using refractive optics to a comfortable f 6.3. You can then piggyback a good quality, short focal length refractor on your reflector and use this either as a guidescope for the...

Collimation of an SCT

As mentioned earlier, the definitive explanation for the precise colli-mation of a Schmidt-Cassegrain telescope is given here by Thierry Legault http legault.club.fr collim.html I cannot describe the procedure any better than this However, there are a couple of practical tips that might make this process a little less tiresome for you. It is essential that the out of focus star you are trying to make symmetrical lies precisely in the centre of your field of view when carrying out the...

First Light your First Objects

I really envy you this moment It doesn't matter how good, or bad, this first image of yours turns out, it is your first light with your new system and you will always remember this evening as something special. For your first image I strongly recommend you pick the largest, brightest object in the sky at the time as discussed in the previous Chapter. This might be a cluster, globular or open, or a bright nebula, Orion if it is up is ideal. Go through your star alignment routine if you are using...

Permanent Setup

You can have the greatest imaging system on the planet, but unless it can be up and running quickly, usually between breaks in the cloud, it may end up simply being a dust-magnet. The problems associated with not having a permanent base for your imaging system are huge, but they are certainly not insurmountable. Many people do not have the luxury of an observatory in their garden, or at a local dark site. In these cases they have to limit themselves to smaller aperture telescopes so that they...

Hyperstar Imaging

Basing your deep-sky imaging on the Hyperstar lens assembly from Starizona http www. starizona.com is sufficiently differentiating that I feel the subject deserves its own Chapter. Figure 1.1 shows the Hyperstar lens assembly for an 11 Celestron Nexstar GPS scope. This is an earlier model that does not incorporate collimation screws as part of the Hyperstar lens. The Hyperstar lens replaces the secondary mirror in a Schmidt-Cassegrain type reflector and turns the SCT into a Schmidt Camera...

The Images

The majority of the full-colour deep-sky images presented in this book in Chapter 11 are from the Hyperstar setup, and many have been published in either Astronomy Now or The Sky at Night magazines. Details of the imaging parameters accompany the corresponding image. There are some images from the Sky 90 with the SXV-H9C camera included for comparison with the Hyperstar work. You will see that the Sky 90 with SXV-H9C colour CCD combination gives a 40 larger F.O.V. than the Hyperstar with...

Forming a Mosaic

The last basic thing I would like to show you to do is how to create a mosaic. If your field of view is just too small for the object you would like to capture, then one way of imaging the object is to create a mosaic of the region by taking several frames and stitching them together. I shall tell you about my 4-frame mosaic technique that allows you to do this easily. Another reason for creating a mosaic is to get a high-resolution image of a region by stitching together several lower...

Narrowband Imaging and Light Pollution Filters

As mentioned previously, I always have an IDAS LP filter in the optical train. This filter cuts out emissions from common light-polluting sources (sodium and mercury vapour lamps) and as a bonus I find I do not need to radically alter the colour balance of my one-shot colour images. I have tried other nebula or light pollution filters and have found it necessary to make substantial colour balance changes to get a good colour-balanced image. Also mentioned previously was the Hydrogen Alpha...

Refractor or Reflector or Perhaps Both

You will need a good quality telescope for deep-sky imaging and these come in two flavours, refractors or reflectors. Refractors are the ones with the objective lens at the front, reflectors utilise a big light-collecting mirror and come in several different configurations. So here's your first big decision, refractor or reflector, and what size Also these telescopes seem to come with a variety of different mounting and control options, Altazimuth, equatorial and goto. Which do you choose...

Quick Process of a Single Frame of the Pleiades

This first example will use stacked, colour-converted data from a single Hyperstar frame of the Pleiades. Please download the unprocessed .jpeg file from jpg where you will find an unprocessed image of Merope and its associated nebulosity as the central part of the frame. This image is made up from 70 sub-exposures of 1 minute per sub taken with the Hyperstar SXV-H9C combination. Having a reasonable number of subs means the final stacked image will have a pretty good signal to noise ratio,...

Reflecting Telescope as the Main

So now let us consider reflecting telescopes, which are telescopes with a mirror as the main light-collecting element. These come in lots of different flavours such as Newtonian, Schmidt-Cassegrain (S.C.), and Ritchey-Chretien (R.C.) to name just three. Since the main collecting and focusing element is a mirror, the big advantage reflecting systems have over refractors is the much-reduced chromatic aberration (C.A.), and this is very important for imagers. There may well be chromatic aberration...

Subexposure Times with the Hyperstar

There are an upper and lower bound to consider when considering the optimum sub-exposure time to use. The lower bound is governed by the shortest sub you can take before CCD noise becomes intrusive. For the SXV-H9C camera, with the Hyperstar, and my typical imaging conditions, this would typically be around 5 seconds or so. The upper bound is where sky glow limits your integration time so that your dim deep-sky objects get lost in the sky background. You must clearly operate well below the time...

The CCD Camera

There are a large number of CCDs suitable for astronomical imaging on the market. There are sub-mega pixel, multi-mega pixel, black and white, single shot colour, imaging and autoguiding CCDs. It is very bewildering especially when there's all this talk about the field of view you get with different telescope CCD combinations and the even more puzzling question of how many arcseconds per pixel your system delivers. Do we need to know the numbers involved in fine detail, or can we just trust to...

Subexposure Times

I don't believe I have come across a topic that causes more contention and tension on the various forums than the subject of optimum sub-exposure time, and with it the total exposure time needed for acquiring a great image For sub-exposure times there are two boundary conditions, the lower bound and the upper bound. The lower bound is the shortest sub-exposure you can take before the CCD noise becomes the predominant source of noise. For the Hyperstar system and SXV-H9C camera with IDAS LP...

Preface

I have recently discovered the most satisfying hobby so far, and to be frank, I have pursued quite a few hobbies in my time This one encompasses computers, optics, precision mechanics, digital image processing and artistic appreciation, and it therefore satisfies just about every major interest I have in one go. The hobby is taking photographic images of the deep-sky. I have not met anyone, so far, that has not been moved, sometimes to a great extent, by the images you will find within the...