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About hamishbarker

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  1. Yes, I was thinking about that the other day. I guess the internal reflection would be at least 4-6% so no good if one is trying to achieve a decent S/N. I will have a look. I've been concentrating my spare time on finishing the figuring of a big telescope mirror which has been lingering for a couple of years. Multiple images in the guiding camera are not such a big problem I suppose, especially if they are only faint.
  2. An old thread but perhaps worth a repost: I scavenged some nice front surface mirrors (presumably alu on glass) from an old scanner/printer. There were 5 mirrors! I tried making reflective slits by cutting the alu lightly with a hobby knife along a straight edge. Testing with a laser pointer and measuring the diffration pattern indicated that light scoring made a 23um slit, while heavier pressure with a dull tip made about 50um slit. Looking at the slit under a magnifier, it looks nice and straight. So will try it in my home built transmission scope (uses old pentax 50mm and 28mm lenses and a piece of 1000lpmm plastic transmission grating but the home made pencil sharpener slit was not even and not reflective)..
  3. i printed some transparency gratings on the laser printer. Looking at them with a magnifier, I found that the 600/1200 dpi (according to specs) printer at work could really only achieve about 4 lines/mm.Lower than this, the lines are made up of circular dots so are too rough. I also got a few printed on a big machine at the local print shop. A little better resolution. However the main problem is that the transparencies are not very optically good (at least after being exposed to the heat of a laser printer), and seem a little...cloudy is the best way to describe it. Putting them on the front of my 200mmf6 newtonian, I can see spectra, but the zero order image and spectrum clarity is poor, presumably due to the transparency not being very good. I did find an old paper by Arthur Vaughan made full aperture gratings (called amplitude gratings) for the Palomar 48 inch schmidt camera to make spectra of the very wide field survey pictures which this instrument could make (back in the days of glass plates bent onto a curved film holder (wince!). They used the thinnest commercially available grades of mylar film, and ruled the grating with a finely lapped fountain pen. Tedious I guess, but it worked apparently. I guess the problem I had with overhead transparencies might have been related to them being much thicker, and then varying in thickness even more after exposure to the heat of a laser printer. http://adsabs.harvard.edu/full/1970PASP...82.1133V The paper has curves for the theoretical grating efficiency at different diffraction orders, which are a function of the amount of black / clear space per ruling.
  4. After a false start and frustration last year, I had success with ISIS by Christian Buill et al. http://www.astrosurf.com/buil/isis-software.html After reading the use guides thoroughly, it works great, but is sensitive to the FITS headers. blank exposure time and lack of obs date and obs end caused errors. My images were taken with a DSLR and when converting RAW to FITS formats with Nebulosity, there was no way to fill in the exposure fields. However, using a fits header editor, ( i used fits4win2 here: http://astroshed.com/fits4win/f4w2hdudoc.htm I edited the headers and now it works really well, with excellent ability to automate the processing.
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