Starlight Xpress SXV-M7C User Manual

Handbook for SXV-M7C Issue 1 June 2004

Starlight Xpress Ltd

SXV-M7C

CCD camera user manual

Thank you for purchasing a Starlight Xpress CCD camera. We hope that you will be very satisfied with the results. The SXV-M7C is a high-resolution ‘one shot colour’ cooled CCD camera, especially designed for astronomical imaging. Starlight Xpress Ltd was the first astronomical camera manufacturer to introduce one-shot colour to the market and we are still the leaders in this technology. The SXV-M7C uses a Sony EXview CCD, with 752 x 582 pixels in a 6.5mm x 4.8mm active area. EXview devices have the greatest quantum efficiency of any interline transfer CCD currently

Handbook for SXV-M7C Issue 1 June 2004

available and the use of ‘secondary colour’ filters on the CCD surface gives the greatest possible throughput of light to the pixels. This camera is a next generation version of the parallel port driven MX7-C, but the use of an internal USB2 interface and the addition of an external guide camera option makes it considerably more effective.

The synthesis of image data from a colour filter matrix CCD is somewhat complex and may be performed in several different ways. We have chosen to do this by creating a high-resolution ‘luminance’ file and combining this with lower resolution red, green and blue, ‘chrominance’ files. This has the advantage of separating the major image processing operations from the colour information generation, so that good colour balance can be preserved while processing the luminance file. When the image is first downloaded from the camera, it is shown in monochrome, as the colour data is still hidden in the fine scale pixel values and it needs to be extracted by mathematical processing of the image data. The software provided will perform this function with a few simple mouse clicks.

Please note that the SXV-M7C can be operated in several different imaging modes. The easiest to use is ‘Fast’, which creates a colour image from a single exposure and so this is the mode used in the operating instructions below. ‘Fast’ mode does give a slightly reduced vertical resolution in the output image, but this is barely detectable unless observing conditions are extremely good. ‘Progressive’ and ‘Interlaced’ modes will be described later.

Please take a few minutes to study the contents of this manual, which will help you to get the camera into operation quickly and without problems. I am sure that you want to see some results as soon as possible, so please move on to the ‘Quick Start’ section, which follows. A more detailed description of imaging techniques will be found in a later part of this manual.

‘Quick Starting’ your SXV-M7C system

In the shipping container you will find the following items:

1) The SXV-M7C camera head.

2) A power supply module.

3) A 3 metre USB camera cable.

4) An adaptor for 1.25” drawtubes.

5) A diskette with the ‘SXV_M7C’ software.

6) This manual.

You will also need a PC computer with Windows 98SE, Windows 2000 or Windows XP. This machine must have at least one USB port (ideally USB2.0) and at least 64 Megs of memory. If you intend to view the finished colour images on its screen, then you will also need a graphics card capable of displaying an image with a minimum of

Handbook for SXV-M7C Issue 1 June 2004

800 x 600 pixels and 65,000 colours. A medium specification Pentium with between 500MHz and 3GHz processor speed is ideal.

Connecting up:

Plug the 5 pin DIN connector into the socket on the power supply box, and plug the power supply into the wall socket. The yellow LED on the power supply should light.

Handbook for SXV-M7C Issue 1 June 2004

Connect the miniature 4 way power plug to the socket on the rear of the camera and screw the retaining ring into place. The LED on the rear of the camera will light a dim yellow. The other connections should not be attached until after the software has been installed.

Installing the software:

Switch on the computer and allow it to ‘boot up’. Once you have the system ready to run, insert the program disk into your CD drive and select ‘Setup.exe’ if the disk does not autostart. The initial installation is to set up the USB drivers required by the SXV electronics. The files SXVIO.sys and Generic.sys are copied to your Windows\System32\Drivers folder and SXV_M7.inf is copied to Windows\Inf. After this, the program ‘SXV_M7C.exe’ will be installed into your ‘CCD’ directory and a new directory called ‘Autosave’ will now exist on the same drive. ‘Autosave’ is where SXV_M7C will normally store its configuration file, ‘SXVM7C.ini’, and any image files, which are recorded using the ‘Autosave’ mode in SXV_M7C and saved in FITs format.

You now need to set up the camera control defaults (shown above), as follows: Start SXV-M7C by clicking on the icon and select the ‘File’ menu. Now select ‘Set program defaults’ and a window, which contains the various software settings, will appear. Suggested starting defaults are as follows:

1) Camera Offsets Both disabled

2) Background Image area Red (or as preferred)

Handbook for SXV-M7C Issue 1 June 2004

3) Interlaced image smoothing On

4) FITS Unsigned Integer format Off

5) Star mask size (area used for photometry and guiding) 8 pixels

The other default settings are not important for current purposes and may be left as the software start-up values for now.

Recording your first image:

We now have the camera and computer set up to take pictures, but an optical system is needed to project an image onto the CCD surface. You could use your telescope, but this introduces additional complications, which are best avoided at this early stage. There are two simple options, one of which is available to everyone:

1) Attach a standard ‘M42’ SLR camera lens to the SXV-M7C, using a 27mm spacer to achieve the correct focal distance. M42 thread spacers are available from most photographic stores, or from Starlight Xpress dealers.

2) Create a ‘Pin hole’ lens by sticking a sheet of aluminium baking foil over the end of the 1.25” adaptor and pricking its centre with a small pin.

Handbook for SXV-M7C Issue 1 June 2004

If you use a normal lens, then stop it down to the smallest aperture number possible (usually F22) as this will minimise focus problems and keep the light level reasonable for daytime testing. The pin hole needs no such adjustments and will work immediately, although somewhat fuzzily.

Point the camera + lens or pinhole towards a well-lit and clearly defined object some distance away. Now click on the camera icon in the toolbar of the SXV-M7C software

Handbook for SXV-M7C Issue 1 June 2004

and the camera control panel will appear (see above). Select an exposure time of 0.1 seconds and press ‘Take photo’. After the exposure and download have completed (between 1 and 3 seconds) an image of some kind will appear on the computer monitor. It will probably be poorly focused and incorrectly exposed, but any sort of image is better than none! In the case of the pinhole, all that you can experiment with is the exposure time, but a camera lens can be adjusted for good focus and so you might want to try this to judge the image quality that it is possible to achieve.

One potential problem with taking daylight images is the strong infrared response of the SXV-M7C. Although the colour filters give good selection of the visible wavelengths, they pass a significant amount of infrared light that can change the colour rendering. This will dilute the colours of green plants (chlorophyll reflects strongly in the IR), and will cause ‘soft focus’ with camera lenses. You can take good images of many artificially coloured objects, but grass and trees will look ‘washed out’. Soft focus with camera lenses is much reduced by keeping the aperture setting below F8. IR blocking filters are available from various suppliers (True Technology, Edmunds etc.) and are recommended for best results.

If you cannot record any kind of image, please check the following points:

1) Is the power LED on?

2) Does the software indicate that the camera is successfully connected? An attempt

to take a picture will fail with an error message if the USB is not properly installed. In this case, try unplugging the USB cable and then reconnecting it after about 5 seconds. Restart the camera software and see if it can link now. If not, check in Windows device manager (via ‘System’ in ‘Control Panel’) and see if the BlockIO device is installed properly.

3) If you cannot find any way of making the camera work, please try using it with

another computer. This will confirm that the camera is OK, or otherwise, and you can then decide how to proceed. Also check on our web site to see if there are any updates or information about your camera software that might help. The message board might prove useful to ask for help with getting your camera operating properly.

Our guarantee ensures that any electrical faults are corrected quickly and at no cost to the customer.

Decoding the image to colour:

Once you have a reasonably clear and well-exposed image, you might like to try generating a colour picture from it. The procedure is quite simple and may be carried out as follows:

1) Check the ‘Set program defaults’ menu and ensure that the ‘Pixel’ and ‘Line’ offsets are both unselected.

2) Click on ‘Colour’ in the main menu and then select ‘Synthesise Colour Image’.

3) Select ‘Apply Anti-Alias’, but leave the other options switched off.

4) Click on ‘Create Image’.

Handbook for SXV-M7C Issue 1 June 2004

After a few seconds a recognisable colour image should be displayed, although the colour ‘balance’ may need correction. This is especially true if your image was taken indoors with artificial lighting, which can make everything look very orange. If the colour image shows white spots or patches, where no colour is present, then the original exposure time was too long and some pixels are overloaded. In this case, you need to take a new image with significantly less exposure time, or with the lens stopped down a little further.

Correcting and refining the colour image:

The colour balance of your image may be adjusted by selecting ‘Colour’, followed by ‘Set Colour Balance’.

You are presented with three histograms, which represent the Red, Green and Blue content of your image, with limits, which can be adjusted by slider controls. A good quality colour image will present three, roughly similar; histograms, and any small colour bias may be seen as different offsets above zero and different widths of the main bulk of the histograms. Moving the lower limit setting of a histogram will adjust the overall colour bias of the picture, with the amount of the particular colour concerned being reduced by moving the limit in the positive (to the right) direction. The location of the pointer represents the new ‘zero’ of the histogram. For instance, if your image is a little too red, you can reduce this by setting the lower pointer on the red histogram to, say, 4, and then clicking on OK. Equally, you can increase the red content by reducing both the blue and green content.

In some cases, there may be a difference in colour bias between the faintest and brightest objects. When this happens, first reduce the error of the faint detail, using the ‘START’ sliders, and then correct the bright objects by using the ‘MAX’ sliders. The ‘MAX’ slider allows you to vary the ‘slope’ of the transfer curve and so change the way that the balance alters from faint to bright detail.

Handbook for SXV-M7C Issue 1 June 2004

Other options in the ‘Colour’ menu are ‘Apply Anti-Alias’ and ‘Adjust Chrominance’. We have already used the Anti-Alias filter as an option during colour synthesis, but it will be helpful for you to know its purpose. Basically, the AA filter is designed to remove colour errors at sharp transitions of brightness. Because of the spatial characteristics of the grid of filters on the CCD, a sharp edge in the image will overlay certain filters, but miss adjacent ones. When the colour synthesiser equations process the data from this region, there will be an incorrect result when these pixels are processed and a line of abnormal colour will follow the transition edge. This is well seen in images of stars, which often take on a strong colour bias, quite different from the expected star colour. The AA filter scans the colour image data and searches for fine details with rapidly changing colours. Wherever these errors occur, the filter substitutes the equivalent and equal values of red, green and blue, thus changing the deviant colour into neutral grey. The result is a much smoother colour image, with clean transitions around stars and other fine details. The AA filter may be used as many times as is desired, but its additional effects will be very slight after about 3 passes of the image. The ‘Adjust Chrominance’ option is not needed for most images, but can be useful for removing atmospheric dispersion from images of the planets. ‘Adjust Chrominance’ permits you to move the red and blue frames with respect to the green frame and so compensate for the displacement of the colours caused by the atmosphere. To use the AC function, shift the red and blue images until the planetary disc has an evenly coloured periphery and any red and blue fringes disappear.

Other image enhancements:

Your first colour image may now be approximately the correct colour, but it is unlikely to be as clear and sharp as it could be. Improved focusing and exposure selection may correct these shortcomings, and you may like to try them before applying any image enhancement with the software. However, there will come a point when you say, “That’s the best that I can get” and you will want to experiment with In the case of daylight images, the processing options are many, but there are few that will improve the picture in a useful way.

The most useful of these are the ‘Normal Contrast Stretch’ and the ‘High Pass Low Power’ filter. The high pass filter gives a moderate improvement in the image sharpness, and the effects of image processing. this can be very effective on daylight images. Too much high pass filtering results in dark borders around well-defined features and will increase the ‘noise’ in an image to unacceptable levels, but the ‘Low Power’ filter is close to optimum and gives a nicely sharpened picture, as above.

The ‘Contrast’ routines are used to brighten (or dull) the image highlights and shadows. A ‘Normal’ stretch is a simple linear operation, where two pointers (the ‘black’ and ‘white’ limits) can be set at either side of the image histogram and used to define new start and end points. The image data is then mathematically modified so that any pixels that are to the left of the ‘black’ pointer are set to black and any pixels to the right of the ‘white’ pointer are set to white. The pixels with values between the pointers are modified to fit the new brightness distribution. Try experimenting with the pointer positions until the image has a pleasing brightness and ‘crispness’.

Handbook for SXV-M7C Issue 1 June 2004

At this point, you will have a working knowledge of how to take and process an SXVM7C image. It is time to move on to astronomical imaging, which has its own, unique, set of problems!

*********************************************************************

Astronomical Imaging with the SXV-M7C

1) Getting the image onto the CCD:

It is fairly easy to find the correct focus setting for the camera when using a standard SLR lens, but quite a different matter when the MX7 is attached to a telescope! The problem is that most telescopes have a large range of focus adjustment and the CCD needs to be quite close to the correct position before you can discern details well enough to optimise the focus setting. An additional complication is the need to add various accessories between the camera and telescope in order that the image scale is suitable for the subject being imaged and (sometimes) to include a ‘flip mirror’ finder unit for visual object location. A simple, but invaluable device, is the ‘par-focal eyepiece’. This is an eyepiece in which the field stop is located at the same distance from the barrel end, as the CCD is from the camera barrel end.

Handbook for SXV-M7C Issue 1 June 2004

When the par-focal eyepiece is fitted into the telescope drawtube, you can adjust the focus until the view is sharply defined and the object of interest is close to the field centre. On removing the eyepiece and fitting the CCD camera, the CCD will be very close to the focal plane of the telescope and should record the stars etc. well enough for the focus to be trimmed to its optimum setting

Several astronomical stores sell par-focal eyepieces, but you can also make your own with a minimum of materials and an unwanted Kellner or Plossl ocular. Just measure a distance of 22mm from the field stop of the eyepiece (equivalent to the CCD to adaptor flange distance of the camera) and make an extension tube to set the field stop at this distance from the drawtube end. Cut-down 35mm film cassette containers are a convenient diameter for making the spacer tube and may be split to adjust their diameter to fit the drawtube.

Another popular solution to the ‘find and focus’ problem is the ‘flip mirror’ unit. These operate on a similar principle to the single lens reflex camera, where a hinged mirror can drop into the light path and reflect the image through 90 degrees into a viewing eyepiece.

In this case, the camera and eyepiece are made par-focal with each other by locking up the mirror, focusing the camera on an easy object, such as a moderately bright star and then flipping the mirror down to view the same star with the eyepiece. Once the eyepiece has been locked into the correct position, you can use it to focus on the image by lowering the flip mirror and operating the telescope focus wheel until the image is sharp. When the mirror is raised, the image will fall onto the CCD surface and should be accurately in focus. Most flip mirror units allow several adjustments to be made, so that the image can be centred properly in the eyepiece and CCD fields, which are not necessarily coincident when you first buy your unit!

+ 24 hidden pages