Re: ATM 16" or 18" (first) DOBS

[Carl Woebcke <carlw@telis.org>]

Jay Anderson, et al,
 
I should have written "(whatever that means)" after "selective bandpass
filter". But, as do you, I believe it means that it only admits light in
a certain part of the spectrum.

You wrote, "I know that the lower the focal ratio the faster the
scope... in other works the more light it gathers so dimmer deep space
objects can be seen better."
Isn't it true that the amount of light gathered depends ONLY on
aperture, and that therefore scopes the same aperture but of different
focal lengths all gather the same light?  And that therefore ALL objects
in them appear EQUALLY BRIGHT (or dim) INDEPENDENT OF FOCAL LENGTH?  I,
too, need to know if this is indeed true.

How apparant is the difference in CONTRAST and/or MAGNIFICATION (where
the hell is underlining?) in a 16" or 18" Dobs between f4.5, 5.0 or 5.5?

I share your intention of including "an inset to bring the focuser right
up to the edge of the light cone", possibly for the same reason: to
reduce the size of the diagonal mirror and increase the contrast. And
then where in the focuser do you assume the focal plane to be, so that
you know where to vertically position the focuser?  

Can I use a "curved spider vane" on a 16" or 18" to reduce diffraction
spikes.

I'm baffled by "light baffels".  How important are they, and where do I
put them?

Can you, Jay, get away with "4 parallel truss tubes"?  Don't you need
the surrrier construction to keep the frame from laterally deforming?

Thanks
Carl Woebcke