Barlow et chromatisme

[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

[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.

[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