Handbook for the SXVR-H18
Issue 1 March 2010
8
Our guarantee ensures that any electrical faults are corrected quickly and at no cost
to the customer.
Enhancing your image:
Your first image may now be reasonably good, 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 various filters and contrast
operations. 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 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.
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’.
At this point, you will have a working knowledge of how to take and process an
SXVR-H18 image. It is time to move on to astronomical imaging, which has its own,
unique, set of problems!
*********************************************************************
Astronomical Imaging with the SXVR-H18
1) Getting the image onto the CCD:
It is essential to set up a good optical match between your H18 and your telescope.
The H18 has a large CCD area and so many of the popular ‘SCT’ ‘scopes are unable
to provide good quality star images over the large chip. Because of this limitation, the
H18 was designed for use with a wide field highly corrected refractor, such as the
Takahashi FSQ106 or similar, but some flat-field reflectors will be OK. A particularly
good option is the ‘Hyperstar’ adaptor from ‘Starizona’, which works well with the
larger SCT ‘scopes.
