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Summary of suggestions for an improved planetary Newtonian:
Gleaned from the CN thread and elsewhere:
High quality, preferably longer focus primary mirrors and preferably in the 8-10" diameter range are vital to image quality.
Use a carefully sized elliptical flat of known high quality to match a low profile focuser.
Use a reasonably low profile focuser. No need for micro focusing in a slower telescope. Spend the bling funds on fast imaging systems.
A well over-dimensioned cardboard tube will help to maximise the potential of any Newtonian optics. External reinforcement may be necessary with thinner cardboard tubes. All tubes will sag to some degree. Particularly thin metal ones! Tube flex will place the on-axis area of best image quality outside the field of view.
Avoid baffles in specialist planetary instruments. They hinder cooling airflow and push warm air currents into the light path due to turbulence.
Use full, well spaced mounting rings rather than small dovetails for maximum tube stiffness and stability.
Avoid large masses of metal in the area of the light path if possible. Heat will rise from it for hours.
A curved spider removes the visible diffraction common to typical straight armed spiders. Particular curved spider designs are favoured for their specific geometry. Do some homework.
Thin spider vanes are essential but must be stiff enough to avoid flexure. Steel vanes can be made thinner than aluminium if lightness is not considered vital. Hardened brass strip is another possibility.
Primary mirror clips/side restraints must not protrude onto the mirror surface because this causes diffraction too.
A small cooling fan (or fans) will help to remove heat from the mirror blank and sweep unwanted warmth out of the top of the oversized tube.
Large airflows are not necessary. The original instruments in the CN thread used thermostats to slow the fans. Computer fans are readily available. As are electronic speed controls for making silent computers.
Blow air onto the back of the mirror and allow it to flow around the mirror blank and on up the tube.
Side fans will help to speed up cooling of the mirror blank but do not have much effect on improving detail and contrast.
Side fans did NOT replace a bottom fan in repeated tests and may be switched off during observation once the mirror is cool. Otherwise they will only stir the warm air currents in the tube and hinder airflow.
Avoid any vibration from the fans. Rubber band mounting can help. Pony tail hair bands have proved longer lived . Rubber O-rings can last for years.
Avoid open/truss tubes which allow body heat to pass through the optical path.
A rotating head or tube will allow you to place yourself on the opposite side of the tube. (Where your body heat is being carried over the top of the tube by a breeze)
It will also improve comfort. A comfortable observer can see far more detail.
Concentrate on blackening the tube opposite the focuser to improve contrast.
Make the main tube longer beyond the spider/focuser to avoid stray light entering the eyepiece.
Avoid stray light entering the tube around the mirror cell.
A steady, driven equatorial mounting allows the observer to study an object continuously.
An object moving across the field of view will not share its fine detail. Nor will a wobbling one!
Avoid placing your telescope on sun-warmed concrete or tarmac.
Store the OTA in an unheated room, garage or shed if it must be taken indoors between observing sessions.
Observing from a (safe) raised platform will put you above rising heat currents from the ground. It will simulate the benefits of a long refractor with its nose high in the air.
A balcony is not the same thing at all. The wall below most south facing balconies will leak stored heat into your view. As will observing from flat roofs or roof valleys. It would be difficult to insulate any roof over a heated building well enough to allow a dome to be placed up there in winter. During warmer weather the roof will absorb vast amounts of heat. Then release it all day and night.
Link to valuable Newtonian design software. Newt for the Web
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