dodsonian v Newtonian

[poider]

G'day, I have seen a few articles about the inabilities of Dobsonians for astrophotography, but I have seen plenty of newtonians advertised for astrophotography, I was under the impression that 'dobsonian' is just the mount and that a newtonian on a lazy susan is a dobsonian, and that a newtonian on a azi or eq mount is a newtonian.
If the same tube can be called different things depending on the type of mount then why is the dobsonian so hard for astrophotography and not the newtonian?
Peter

[bojan]

You were right, Newt is OTA (Optical Tube Assembly) and dob is Alt_Az mount in nutshell, without anything else (motors etc.).
Dob is not hard for AP, but not easy either, because it lacks tracking, and when it has it, usually there is a problem with field rotation (in case of longer exposures and in some directions on the sky... not relevant for planets and Moon though).

To motorize Dobsonian, have a look here:
http://www.bbastrodesigns.com/StepperSystem.html
or here:
http://www.stellarjourney.com/index.php?r=site/equipment_onstep
http://soundstepper.sourceforge.net/

[raymo]

The same tube is not called different things Peter; the name Dobsonian
is the name given to the whole assembly of a Newt mounted on a simple
lazy Susan[in effect an alt/az mount]. I suppose it is a little confusing because there is no name given to the whole assembly of a Newt on an EQ mount. The Dobsonian is named after John Dobson who built them as a cheap
way of getting into large [as in huge] scopes.
raymo