Barlow et chromatisme

Design, construction, tuning of spectroscopes
Information and discussion about softwares (telescope remote, autoguiding, acquisition, spectral processing ...)
Robin Leadbeater
Posts: 1926
Joined: Mon Sep 26, 2011 4:41 pm
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Re: Barlow et chromatisme

Post by Robin Leadbeater »

Hi Tom,

Yes sorry, my calculations have gone awry somewhere. I should have said 2.4 arcsec for the ALPY and the standard 23um slit (can you get a 35um slit?) and 1.8 for the LHIRES and 35um slit. There is a resolution penalty going to 35/50 though of course.

Unless they have updated it the open aperture of the LHIRES 200mm fl doublet is f8 but the ingoing and return beams are at a slight angle and the return beam is dispersed so I think there must be some vignetting at f8, though perhaps it is minor.

Cheers
Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
Tom Love
Posts: 64
Joined: Sun Apr 21, 2019 5:57 am

Re: Barlow et chromatisme

Post by Tom Love »

Yes, checking with Francois there are quite a few different Alpy slits available. I've gone for 35 microns to start with, and ~3.5 arcseconds should work for a reasonable proportion of the time. The Lhires at the longer focal length will be a trickier proposition. I have a range of targets with different resolution requirements, so will need nights of good seeing for some of them, whereas others will be viable with a larger slit in a wider range of conditions.

To be fair, I am considering whether a) an eShel would make sense (though expensive), or b) a custom cobbled together instrument a bit like a Vhires would be the best option for the medium term, allowing full exploitation of the aperture with a higher level of resolution. But in the immediate future I should be able to make reasonably good use of the Alpy and Lhires. And I'd hope that the Alpy at native f/4 and 2m focal length should work nicely.
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Martinborough, New Zealand. Alpy, Lhires RC12
Michel Verlinden
Posts: 191
Joined: Tue Aug 16, 2016 12:11 am

Re: Barlow et chromatisme

Post by Michel Verlinden »

Bonjour à tous,
Quelqu'un aurait-il des résultats ou des simulations pour d'autres rapports d'ouverture (FD=3.3 ou 4) et avec l'APM 2.7x ou le baader FPC 3X-8X utilisé à 3X (matériau : CaF2) ?
En combinaison avec l'UVEX, les barlows testées aggravent-elles l'astigmatisme ?
Amicalement,
Michel Verlinden
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