Re: [ATM] Why Lurie-Houghton telescope very rare in the ATM

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

Hi Greg,
I remember to saw your web-pages of Lurie-Houghton Newton telescope but I 
didn't know that you have made your telescope already10 yrs ago!

I think you comments are right about why there exists only a few of us LHN 
telescope builders. I also like to say that the am. optics are  in real quit 
easy to make and all the good news I had heard before seem to be true in 
real. Just had heard somewhere about that cooling problem. As I earlier said 
haven't yet noticed any major cooling problems and as you said lenses are 
thin and no optical power!

I really think so that LHN telescope is worth of making. My 6" telescope was 
just a prove to myself that I can. 8" Lurie-Houghton is the next goal, 
hopefully in near future.

Regards,
Aki Lötjönen
http://koti.phnet.fi/lottaki




On Thursday 11 August 2005 08:53, Greg Jones wrote:
> I'm not sure if mine was first or second to see star light but was at OSP
> in 1995 and Table Mountain in '96 (ATMJ #10).  I think there are several
> reasons you don't see too many.
>
> First, it is a fairly new design, and the design was presented not the
> scope.  It took a leap of faith to build one.
>
> Second, I think the lenses scare a lot of people and really shouldn't, they
> are fairly easy, just a lot of surfaces.  I've always thought I would
> re-figure mine (it was the first scope I completed from blanks) but haven't
> yet.  Once re-figured I'll send the lenses out for an AR coat which I also
> think is a must for optomum performance.
>
> Cost is a factor but again, less than many think.  The lens glass can be
> ordered Plano-plano fine ground rather than polished; at quite a savings.
>
> One pro made a LH an claimed it had "too much glass."  OK, I'm not a pro
> but question that analysis.  The first set of lenses for my 8" were from
> .5" blanks.  The second set (a little problem with a door) are from .75"
> blanks. If I did it again I would use either .5" or .625" blanks.  Compared
> to an 8" refractor, the Hubble "eye glasses" et al, I don't see the glass
> quantity as an issue.  For what you get, the design is easy to realize. 
> BTW, the second set took less than 2 weeks start to finish.
>
> My 8", if made correctly has a 1" dia. diffraction limited field and 2"
> with film resolution.  My CCD is 1" square (and not finished.  My cookbook
> is, ummm smaller:-).  Film?  Oh yea, I could use film I guess...  OK, film
> isn't dead, but for CCD work the LH is overkill.
>
> I haven't found cooling to be worse than any other closed tube system.
> Again, the lenses are fairly thin and with zero power...  It does probably
> take longer than a Newtonian, but has not been noticed as a problem.
>
> Last, like any full aperture corrector, the LH has a "sweet spot."  IMHO--
> 8" to 10" is about it.  6" is OK, but kind of small for the effort.  Above
> 10", I think some of the Hyperbolic designs with sub-aperture correctors
> make a lot more sense.
>
> With all that said, if you want an astrograph and have a Dob budget, the LH
> is a great project that is very likely to be completed. No difficult
> surface figures and performance is very good even if you mess up a little. 
> Note every element is null tested or interference tested to a nulled
> surface. I've seen several claims a knife edge null on a spherical mirror
> is better that 1/50th wave...
>
> Hope that helps,
>
>
> Greg Jones
> http://home.comcast.net/~dac20/dac_001.htm
>
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