| article: TeleAuto - the HX916 plugin |
The motivation for the HX916 plugin
First of all I like the user interface of TeleAuto (TA) very much.
Especially changing the binning mode is very elegant.
Just press the corresponding start exposure button.
No nested dialogs and listboxes.
It is important for me to have the 3x binning in fast access because I use it as an electronic finder and for rough focusing purposes.
Another important reason for using TA is the way it is combining and registering frames.
The stellar version is modelling all the stars in the image to match them from frame to frame.
That is very promising.
The actual combination can be done by adding, mean, median or the statistical Sigma-Kappa combining.
What else do you need?
The next big plus with the HX916 plugin is the ability to master bias correct the raw frames automatically.
Why a master bias correction is a serious alternative to dark frame correction with a camera like the HX916 can be found here.
The advantage of the correction right in the plugin is that TA will display a corrected frame.
The frames background is quite close to the sky background or zero in case of short exposures.
That means that the frames are displayed with much less noise and faint objects are much more prominent.
I find this useful for the 3x binning when using it as an electronic finder.
In 1x or 2x binning now there is a much better chance to visually judge the quality of the image with a certain exposure time and check the need to expose longer.
A minor advantage is that the plugin written in C is very fast and able to give a different result for the light frame if the exposure time is varying in 0.001 seconds.
With other plugins I noticed that all exposures were actually the same up to several 0.01 seconds.
This behaviour is depending on the speed of the image acquisition computer.
Mine is a Laptop with 1 GHz processor.
The lowest possible exposure time is useful when the target is very bright like the moon is in telescopes with big aperture.
Last but not least this is the data reduction (frame calibration) for the lazy man and still giving high quality results.
How to create a master bias frame?
In general, a bias (or offset) frame is the frame produced at zero exposure time and in the absence of light.
You can regard it to be a dark frame of zero exposure, hence with no thermal noise in it.
In general he value of ADUs in a bias is surprisingly high.
This is related to the fact that the camera designer has to avoid negative values (due to noise variation) by all means.
These values would produce digital values very close to saturation hence giving horrible signal to noise ratios.
That's why there is always a positive offset above the zero level even in the absence of light and thermal current.
In the case of my HX916 it is in the order of 3.000 with a slight gradient from top to bottom caused by the readout procedure and the indication of faint vertical stripes.
The master bias should contain as less noise as possible.
Otherwise it would introduce noticable noise when beeing subtracted from the light frame.
So it's a good idea to combine as many single bias frames as you will later have combined light frames.
I took 250 for 3x binning, 200 for 2x binning and 150 1x binning to be on the safe side.
So set the exposure time to zero, set loops to 100 or whatever, mark the automatic file save checker and type a name like @1bias (for 1x binning).
TA will generate all the single bias frames with ascending numbers at the end of the name.
When the loop has finished just combine the frames with either mean or median combining.
The mean combining gives a slightly better result for random noise while the median is useful if your single bias frames are contaminated by cosmics.
The resulting file should look similar to a single bias frame - just with much less noise in it.
Depending on the stability of the electronics and the characteristics of the CCD chip a master bias frame can be reused for months.
So the whole procedure does not have to be repeated too often.
Goto TeleAuto main page with images and tuorials.
Download the Starlight Xpress HX916 plugin
The current status of this plugin written in C language is still under development.
Use it on your own risk and without warranty.
These versions are writing a debug file called "spy_hx916.txt".
It will contain further debug information about the last session with TeleAuto.
If someone wants to begin a plugin for the MX516 with parallel port connection I would be highly interested in!
I needed that plugin for auto-guiding and would give support with my source code developed so far.
Please use the send comment link at the bottom of this document.
Download Version 0.9
This version can take images in 1x1 and 2x2 and 3x3 binning.
Now some subwindowing is available but only as a part of a fully downloaded frame and only in full resolution.
The plugin can subtract a master bias before giving the frame data to TeleAuto.
The plugin uses the bias frames only if it can find them.
Otherwise it will not perform any correction and you will get the raw data of the camera.
Whenever a bias correction is performed you should hear a little beep sound in your speakers.
To use bias frames create a directory called: c:\hx916
Now for each binning mode you want to be bias corrected store a file in that directory calles: @1bias.fit, @2bias.fit or @3bias.fit.
The number indicates the binning mode.
The spy file's extension is changed to .log now and the file is located in the c:\hx916 directory, if existing.
Download Version 0.8
This version can take images in 1x1 and 2x2 and 3x3 binning.
No subwindowing is available, only full resolution.
Download Version 0.6
This version can only take images in 1x1 and 2x2 binning.
Never press 3x3 or 4x4 binning or otherwise you will have to reboot the camera and your PC.
No subwindowing is available, only full resolution.
Report Comments and Bugs
Please click here to report a comment or a bug on the HX916 plugin only.
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