Re: Breakthrough Dob or Frightening Abomination?

Hardly a breakthrough. An incremental step. Not frightening, unless someone
was considering selling that scope commercially.

Fast mirrors are nothing new. Cassegrain and related designs have used them
for decades. Using fast mirrors with corrective optics is also not new.
What's new is challenging the lore of what's commercially viable - what
customers will accept and pay for, and manufacturers with enough foresight
to risk offering those more expensive products that push the limits of
conventional "wisdom.". I applaud Steve Kennedy's and Mike Lockwood's
efforts to push the envelope - producing faster, thinner, large mirrors.
Another set of enabling products are the wider field eyepieces that have
been designed to minimize astigmatism from the steep light cones coming from
fast optics (e.g. Naglers and Ethos).

For visual observing, I think fast optics are better suited for very large
scopes - extending the aperture where one can avoid ladders and sit more at
the eyepiece. Yet, commercial scopes using these fast mirrors haven't
updated their designs. Faster mirrors cost more, yet eyepiece height of some
existing scopes could be lowered for little or no cost.

The f/2.55 14" scope is a curiosity at best - more likely an abomination. As
shown, the scope presents more problems than it solves, while adding
significant cost for the superfast optics. I can't imagine anyone wanting
one. I suspect the 14" aperture was selected to demonstrate feasibility on a
modestly-large mirror while keeping cost down before stepping up to larger
mirrors. It pains me to see that mirror in an outdated design - its like
placing a modern racing engine inside a Model T. Hopefully the builder only
used the structure as a simple, quick, inexpensive prototype.

One doesn't need such fast optics to make 18" -20" scopes with convenient
eyepiece heights. The maximum eyepiece height of my 20" f/4 is 65-1/2" - a
sit-down scope for observing almost anywhere in the sky. Also, faster
mirrors only solve some of the issues of larger scopes. A 25" f/2.8 or a 30"
f/2.5 would allow you to keep your feet on the ground. But you still have to
be strong enough, and have a vehicle large enough, to transport it. It has
to fit through your doorways into storage. These constraints are less of an
issue if you are fortunate to house it somewhere permanently. But then,
there is the cost.

Now, if someone could produce large fast mirrors that fold up into half
their volume, weigh half as much, and cost only half as much, that would be
a breakthrough.

Albert

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