Re: ATM Newtonian with a Tilted Secondary (2 Mirror Folded Newtonian)

[Anthony Stillman <atmer@flash.net>]

Mike,

>...looking for was advise from those who have built and
>used a 2 mirror folder Newtonian, regarding design tips, components, and
>usage,

I've built a two mirror folded refractor.  Does that count?


>...good way to mount a focuser
>...flat base, mounted to a custom machined wedge

Yes and, why drill a hole when a slot will do?  Why cut a slot when an
oversized  hole and a couple of washers will do?  Why cut a wedge, when a
plate and a pair of push pull screws will do?  The watch word is slop, ah,
I mean adjustability.


>Does the odd angle of the eyepiece cause problems in some viewing
>situations (sore neck, uncomfortable access to the eyepiece,...)?

Yes, hence the star diagonal.


>Would people who are "left eyed" need the eyepiece to be on the opposite
>side of the tube from people who are "right eyed"?

Not with a star diagonal.


>Are there any techniques for eliminating stray light intrusion into the
>eyepiece since it would now point towards the end of the OTA (other than
>making a very long shroud)?

As with a cass. an oversized secondary obstruction helps.  Baffles near the
draw tube also help.  This was discussed recenly on the list with regards
to the typical un-tubed newtonian design.


>A focuser that angles downward to any great degree might tend to drop
>eyepieces that aren't securely clamped.

If the ocular is expensive or brand new it will jump out of a vertical draw
tube and head for the under side of a shoe the first chance it gets.


>A focuser that angles downward by more than a small amount may cause the
>draw tube to slip when used with heavy eyepieces or a binocular viewer.

I have used only one focuser for which this wasn't an issue.  It was of
helical design.  It was inexpensive, had excess slop and I replaced it
straight away for one that I could adjust between slip and struggle.


>These are issues that come to my mind, but I'm sure there are things I
>haven't considered.  Any other concerns I have overlooked?

I can't overemphasize the value of a laser pointer for collimation.  Tasks
that onece took hours now take minutes.  Tricky alignment's can be
eyeballed to fractions of a millimeter over meters in seconds.  Where onece
I was loath to remove a properly positioned component to reposition another
or take advantage of an otherwise hidden alignment fidutial, now I don't
hesitate, well OK, I don't heitate that much.


Anthony