[APML] Re: M8 from 41 North

[Ray Butler <ray.butler@nuigalway.ie>]

robgendler@att.net wrote:

 > Hi Ray,
 >
 > Thanks. I'm addicted to diffraction spikes  <g> so I placed string over
 > the objective. I think the brighter stars are more aesthetic and the
 > stellar intensities are dissipated to certain extent resulting in less
 > bloated stars.
 >
 > Regards
 >
 > Rob

Interesting! And it now makes sense to me why they were there. I thought 
my eyes were playing tricks for a moment.

I gather that there used be a school of thought in the 1970s (and maybe 
'80s) that telescopic pictures _without_ diffraction spikes were 
"better", because they obviously implied an expensive optical system 
(SCT, Mak, or refractor), not a cheap Newtonian! But Ritchey-Chretien 
systems (like your other telescope) have now dispelled the notion that 
reflectors with secondary vanes are cheap or inferior. Hell, the $6bn 
HST is a R-C design.

Ray "who prefers spikes in aesthetic images, but finds them a nuisance 
in research data" Butler

>     -------------- Original message from Ray Butler : --------------
> 
>      >
>      > Amazing detail, Robert.
>      >
>      > But I am a little confused by one thing. If this was taken with
>     an AP
>      > 155 refractor, why are there diffraction spikes (like from a
>     secondary
>      > mirror support) on the brighter stars?
>      >
>      > Ray "first spotting the Lagoon Nebula with binoculars in 1986 was
>     one of
>      > the seminal moments in my astronomical youth" Butler
>      >
>      > Robert Gendler wrote:
>      > > Hi all,
>      > > I thought this turned out pretty well considering it
>      > > skimmed my neighbors roof and only allowed 1 hour
>      > > of imaging.
>      > > http://www.robgendlerastropics.com/M8LRGB.html
>      > >
>      > > I was going to wait until I got some h-alpha but the weather
>      > > doesn't look like it will break so here it is. 

-- 
Dr. Ray Butler (ray.butler@nuigalway.ie || ray@physics.nuigalway.ie)
Lecturer, Dept. of Physics || Computational Astrophysics Laboratory
National University of Ireland, Galway, University Road, Galway, Ireland.
Tel: +353-91-524411 ext. 3788   FAX: +353-91-525700

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