Quote:
Originally Posted by Kokatha man
Whilst it still seems to me that with the parameters I've previously described I can rotate the baseboard of the Dob to a point where the scope could be defining a specific Hour Angle/Right Ascension, it would be, because of the Dob's physical construction, only aligning with one tiny point along that RA's meridian .
Because the Dob cannot "sweep" along that meridian (unlike the EQ with its' specifically arranged and aligned dual axes) - the validity for targetting using such aforementioned circles becomes nonsensical.)
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Hi Darryl,
You've got it!
I won't address your penultimate post as I believe you have now spotted the
various mistakes in it.
Quote:
Oh well, a thousand apologies and perhaps my one consolation is the bit about a straight Dob being an EQ at the pole: not sure if I'm going to pursue that option of maximizing the plain Dob's potential...
Regards, Darryl.
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No need to apologize at all! There is some mental gymnastics in imagining
how lines of RA and Dec are mapped out in the sky that is not always
immediately apparent to many of the enthusiasts I get to deal with.
As you note, take the Dob to the North Pole or South Pole and it is
an equatorial mount when leveled.
At any other latitude, one could tilt an Alt/Az mount over at an appropriate angle
and it becomes and equatorial mount.
Though equatorial platforms do precisely this job, as a rule, most large
aperture Dobs are operated in Alt/Az mode with the base roughly level with the
horizon. The key to large aperture Dobs is large, light weight, thin, affordable
mirrors. However, such mirrors warp under gravity as the scope moves. The
job of a mirror cell is to act as a set of levers to help counteract the effects
of gravity and to try and keep the mirror in its correct shape. Such mirror
cell designs are usually constructed with the assumption that the scope
was operated in an Alt/Az mode rather than the mount being tilted over
so that its Az axis becomes parallel to the celestial pole. This is the
primary reason you see so many large aperture Dobsonian telescopes
whereas most amateur equatorial mounts usually only are fitted with
more modest aperture telescopes. It is also one of the main reasons
why almost all modern professional observatories also prefer the Alt/Az
configuration from a mechanical engineering standpoint.
Best regards
Gary Kopff
Wildcard Innovations Pty. Ltd.