Re: [ATM] 4-1/4" Mirror Suggestions and Thoughts Wanted

[John Lynch <john_lynch2006@yahoo.com>]

Dave,

I dabbled with NEWT software in designing a short
focal length 4.25" telescope, which seems nice because
it would be small.  However, I recall having some
problem with the apparent vignetting of the larger
secondary mirror to accomodate a rather fat light
cone.  I think the longer focal length system might
avoid this problem because you could use a smaller
secondary mirror with a narrower light cone.

John Lynch

--- Dave Tabor <david@tabor.com> wrote:

> Hi, fellow, ATM'ers...
> 
> I'm a beginning ATM'er, who made his first 8" mirror
> (f/6.25) last winter. 
> I used it to build a travelscope, which works very
> well, but as I'm told is 
> common with ATM'ers, it's my work-in-progress.  I
> recently modified the 
> trusses, going from 4 straight to 8 diagonal.  Now I
> need to re-fix the 
> balance a little, and I'm planning to switch to
> ebony star and teflon to 
> make it smoother.
> 
> I'm going to be assisting my 10 yr old daughter with
> her first mirror, and 
> she's decided that smaller is nicer, so we've
> purchased a 4-1/4" mirror kit. 
> She'd like the scope to be shorter, so it fits her
> size better.  I'd like to 
> keep usable for as many different types of things as
> possible, to help keep 
> her interest in astronomy peaked.
> 
> If I guide her toward an f/6, it would be shorter
> (25.5" focal length), but 
> would need a 3mm eyepiece to get up to the 212x
> theoretical maximum 
> magnification for a 4.25" mirror.
> If she went with an f/12, it would be easier to get
> the 212x for viewing 
> planets, etc., but might limit it's uses.
> 
> Being an beginning amateur, and not having the
> experience to fall back on, 
> I'm wondering what suggestions, thoughts or
> recommendations the group has 
> regarding good usable scope configurations using a
> 4-1/4" mirror?
> 
> Thanks,
> Dave 
> 
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 


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