Facing given light pollution drives me to the decision to open a "new window". Other observers at better location have better conditions to create pretty pictures - so I decided to do something different.
Together with some frends we started working on spectroscopy right from scratch because nobody in our team has experience with spectroscopic observations. So we learn what are the chanllaging topics. More about this team can be found here: PANDORA http://pandora.zitzkowski.de/
After getting in touch with some spectrographs like DADOS I come to the conclusion that the Lhires III from SHELYAK INSTRUMENTS might be the best choice for my "Friesenheimer Lichteimer"
LHiRes mounted at AAF3 Focuser.
Because LHiRes is optimized for f/10 ratio and also to elongate backfocus of the f/4.2 Newton to more than required 70mm a Balow lense with an extension ratio of 2.5 is mounted between focuser and spectrograph.
This extension has a serious impact on practical observation. With an effective focuslength of ~5000mm the linear resolution is about 2µ per arcsec. in case of typical seeing of 2-3 arcsec the size of a star is about 50-75µ. Using slit less than 50µ in order to have higher spectral resolution end in losing light at entrance slit.
Currently I'm collecting experience to find out which mag can be reached by using different slits. A matrix will be created to allow better planing for objects and required exposure times.
The regular slitplate installed provides slit sizes 15µ, 19µ, 23µ and 35µ. it's quite clear that the smallest slits can be used for brighter stars only in order to spectra in higher resolution. For less bright objects I can use broader slits which for sure supports less resolution but allow more light to pass the slit.
Several exercises have to be performed:
- Verification of first observed spectra versus existing data
- relation of slit size and spectral resolution achieved
- understand slit to be used and influence of binning on spectral resolution / details.
- limiting magnitude as function of slit size
- learn data processing procedures to be applied