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Old 19-06-2018, 03:02 PM
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Merlin66 (Ken)
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Join Date: Oct 2005
Location: Junortoun Vic
Posts: 8,904
300 l/mm Objective grating trials

To improve (?) the results from the transmission grating - a la Uwe's tremendous efforts, I set up a 50mm Sq 300 l/mm Thorlabs blazed grating in a Cokin filter holder mounted on a Canon 85mm prime lens and a 1000D (modded) camera.
I used a 60mm finder as an acquisition/ guide scope with the camera off-set by 7.5 deg. Both mounted on a Vixen dovetail on the HEQ5 mount.

The FOV of the 85mm lens is 15 x 10 deg (orientated with the grating dispersion (2.2A/ pixel) along the Dec axis.) This allows the target star to be positioned on the right hand side of the image and the full spectrum recorded within the frame.
A 1 or 2 min exposure gives good results on the brighter stars.

Initial results: Hmmmm - honestly not as exciting as I hoped. Yes, you get good spectra of the field stars and any stars with H alpha emission (Del Sco) show up very well, the final resolution is limited by seeing. The major issue I found was the number of background stars "interfering" with the spectra - it's a lot of work analysing and cleaning the result.

One good "spin off" found, was the the image could still be plate solved (by Astrometry.net) notwithstanding the obvious spectra!

I'll continue the trials a bit longer to establish limiting magnitude v's spectral resolution......
May be do some comparison spectra with the Baader 207 l/mm (only 28mm aperture)
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