Re: [ATM] Luri-Houghton prescriptions.

[Aki Lötjönen <aki.lotjonen@phnet.fi>]

Hi Guy,
Yes, one will loose a considerable amount of light. Just meant a LHN
telescope works quite satisfactory without any corrector lens coatings.
You cannot compare straight to one with and without coatings. I guess
many amateur refractors do not have coated lenses. Ok, in LHN case there
is also two reflecting surfaces before focus point. I haven't tried to
find out any coating service yet. Coatings may be pretty expensive.
But the mirror' aluminum surfaces is good to get with the high
reflectivity ones. 
On the other hand, un-coated lenses are easy and safe to wash if needed.
Something positive..

Aki



> Won't one lose a considerable amount of light by
> having all those non-coated surfaces? At 4 surfaces,
> losing 4% of the light on each one, that reduces the
> transmission to 85%, roughly.
> 
> On our project, we hope to eventually get them coated,
> by whom, I don't know. Calculating the thickensses
> necessary for the various layers, and then getting
> that right, in our vacuum chamber, sounds like not a
> job for amateurs.
> 
> Guy
> 
> --- Aki Lötjönen <aki.lotjonen@phnet.fi> wrote:
> 
> > Hi Bob,
> > 
> > It will be a great telescope! My regards to him who
> > ever is making that
> > 12,5 " Lurie-Houghton Telescope. Wow! I really hope
> > you have time and
> > willing to make that big Lurie-Houghton Newtonian.
> > I read others comments. I have nothing to add. I
> > also think surface
> > pairs is the right way to go. If there is an option
> > to leave secondary
> > spider away, why not to do so. Lens thicknesses from
> > designed can vary a
> > lot, no problems... Lurie-Houghton Newtonians are
> > really forgiving!
> > The lenses need not necessarily to be coated too.
> > 
> > Rgds,
> > Aki Lötjönen
> > 
> > 
> > > I'm planning on coring the lenses to 2" or maybe
> > 2.5" and putting
> > > the mount on them.  Why do a solid front glass and
> > not use it to
> > > support the secondary mirror.  I plan on the edge
> > of the
> > > secondary to be almost touching the rear lens. 
> > The biggest fun
> > > will be insuring that the center spacer is the
> > correct depth for
> > > the edge spacer.
> > > Bob May
> > > bobmay at nethere.com
> > > http: slash /nav.to slash bobmay
> > > http: slash /bobmay dot astronomy.net
> > > Addresses have been munged up to keep spammers
> > from bothering me.
> > > replace the obvious words with the proper
> > character.
> > > Thank you for your understanding!
> > > 
> > > _______________________________________________
> > > ATM mailing list http://www.atmlist.net/
> > 
> > _______________________________________________
> > ATM mailing list http://www.atmlist.net/
> 
> 
> Guy  Brandenburg
> Washington, DC
> My home page:
> http://home.earthlink.net/~gfbranden/GFB_Home_Page.html

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