LOSPEC 3D printed spectrograph
Posted: Tue Aug 28, 2018 5:29 am
Hi all
I have made a LOSPEC spectrograph designed by Paul Gerlach that is available from here https://www.thingiverse.com/thing:2455390.
My first attempt was not great as I found lots of problems that made it difficult to use and underwhelming but I have iron out some of the problems and successfully took some very good spectra last night.
The first problem was a very poor guider image that had terrible astigmatism. The problem was that it was hard to align the guide mirror but I found a way to do it.
First I removed the lens to the guider. I then placed a laser collimator in the front of the spectrograph and aimed it at the slit mirror. The guider mirror holder is a press fit into the slit assembly and can be adjusted a little. I placed a mirror where the guide camera should be and reflected the image back to the laser. By slightly moving the guider mirror I was able to centre the laser. When I tested it with a star the image is now very good.
The next problem was focusing the star image. I focused the guider on the slit but when I took a spectra the image was split and clearly not in focus. I could focus the scope to create a clean spectra but then the guider image was out of focus. I suspected that this was due to the slit that is an OVIO wheel. I had placed it with the mirror surface closest to the scope. I tried it the other way us and this problem seems to have resolved. I do have a ghost image in the guider for very bright stars but this is OK. My LISA and LHIRES also have similar ghost images.
The other very big problem I initially had was very poor sensitivity. I could take a 5 min exposure of a bright star and not saturate the image. A similar star through my LISA would saturate with 10sec. There was obviously a problem. I was using an old 600l/mm grating. I also have a 1200l/mm grating that was in my L200 so decided to compare them. I realised that the 600l/mm grating was not reflecting anywhere as much light as the 1200. The mirror surface was dulled. I put the 1200mm grating in and the difference is amazing.
I took some images last night. This is a single exposure 60 sec exposure of tet1 Sgr (a spectroscopic binary).
Processing in ISIS gives ~R=5000 This is a filly lamp calibration exposure.
I had taken a spectra of the same star with my LHIRES earlier in the night and have compared the 2 images below. The LOSPEC image is 300s. The LHIRES is 1200s Nova Lup 2018 at about mag V=12 900s exposure. This is now a useful functioning spectrograph giving me another choice between my LISA and the LHIRES. The resolution could be improved with a smaller slit. All these images were through a 29um slit with a C11 at F/10. I will try using the scope with a focus reducer and see if it still gives an adequate image. I use the focal reducer with the LISA and this improves the sensitivity.
Terry
I have made a LOSPEC spectrograph designed by Paul Gerlach that is available from here https://www.thingiverse.com/thing:2455390.
My first attempt was not great as I found lots of problems that made it difficult to use and underwhelming but I have iron out some of the problems and successfully took some very good spectra last night.
The first problem was a very poor guider image that had terrible astigmatism. The problem was that it was hard to align the guide mirror but I found a way to do it.
First I removed the lens to the guider. I then placed a laser collimator in the front of the spectrograph and aimed it at the slit mirror. The guider mirror holder is a press fit into the slit assembly and can be adjusted a little. I placed a mirror where the guide camera should be and reflected the image back to the laser. By slightly moving the guider mirror I was able to centre the laser. When I tested it with a star the image is now very good.
The next problem was focusing the star image. I focused the guider on the slit but when I took a spectra the image was split and clearly not in focus. I could focus the scope to create a clean spectra but then the guider image was out of focus. I suspected that this was due to the slit that is an OVIO wheel. I had placed it with the mirror surface closest to the scope. I tried it the other way us and this problem seems to have resolved. I do have a ghost image in the guider for very bright stars but this is OK. My LISA and LHIRES also have similar ghost images.
The other very big problem I initially had was very poor sensitivity. I could take a 5 min exposure of a bright star and not saturate the image. A similar star through my LISA would saturate with 10sec. There was obviously a problem. I was using an old 600l/mm grating. I also have a 1200l/mm grating that was in my L200 so decided to compare them. I realised that the 600l/mm grating was not reflecting anywhere as much light as the 1200. The mirror surface was dulled. I put the 1200mm grating in and the difference is amazing.
I took some images last night. This is a single exposure 60 sec exposure of tet1 Sgr (a spectroscopic binary).
Processing in ISIS gives ~R=5000 This is a filly lamp calibration exposure.
I had taken a spectra of the same star with my LHIRES earlier in the night and have compared the 2 images below. The LOSPEC image is 300s. The LHIRES is 1200s Nova Lup 2018 at about mag V=12 900s exposure. This is now a useful functioning spectrograph giving me another choice between my LISA and the LHIRES. The resolution could be improved with a smaller slit. All these images were through a 29um slit with a C11 at F/10. I will try using the scope with a focus reducer and see if it still gives an adequate image. I use the focal reducer with the LISA and this improves the sensitivity.
Terry