What is guidingGuidingistheprocessofkeepinganobjectbeingimageddeadcentreinthetelescopetoallowforlongexposures. Theguidescopeandcameraarefixedtoyourtelescopeandthecameraisconnectedtoyourmountandsome softwareonyourlaptoporremotePCdependantonhowyou’reconnected.Thecameraisfixedontoastarand thesoftwareanalysesthefeedandsendsminute“push”signalstoyourmounttokeepthisstarcentredonthe screen.Becausethestaris(usually)movingatthesamerateastheobjectthatyou’reimagingthroughyour telescope,bykeepingthestarcentredintheguidecamera,theobjectbeingimagedthroughthetelescopeiskept centred. This means that you can take as long an exposure as your equipment will allow.What you will need1)A guide camera2)A guidescope3)A laptop, mini PC, Raspberry Pi, ASIair or similar4)Guiding software, PHD2 is free and easy to use but a Google search will offer up other options.You will notice two ports on the camera above. One connects the camera to the mount and this is called the ST4 port. The other connects to the USB port to talk to the guiding software.The way it works is like this1)Connect your camera to the mount and laptop2)Start the guiding software and initialise the camera3)Select a star4)The software will now do some calibration by moving the star in the East, West, North and South directions5)Once the calibration has completed you will now be guiding on the selected star and good to go6)The camera sends consecutive short exposures to the guiding software, usually around 3 seconds7)The guiding software analyses each image received from the guide camera and notices any movement of the star8)The software sends a signal to the mount via the camera and tells it to move in the correct direction to counteract the movement of the star, thus keeping the star (and your DSO target) bang in the centreCongratulations, you’re now guiding!!!IfyouconnectyourequipmenttoeitheraminiPC/RaspberryPi/ASIairorsomethingsimilarthenyoucanlose thecameratomountcableandutiliseasettingcalled“PulseGuiding”.Thissettingcanonlybeusedifyourmount isconnecteddirectlytooneoftheabovedevices.Itsendsthecorrection“pulse”directlytothemountinsteadof via the camera and this can help with cable control.
Inordertoobtainthelengthyexposuresneededforimagingdeepskyobjects(DSO)thenyouwillneedtoadda process(andmoreequipment)toyoursetup.Pairedupwithanequatorialmountaguidecameraandguidescope will enable your setup to greatly extend your exposure times to capture those all important photons.WhenimagingaDSOyouneedtoletasmuchlightfallontothesensorasyoursetupwillallow.Thelongeryou canallowthelighttohitthesensor,themorelightdatabuildsupintheimagefile.Youthentakeaseriesofthese long exposures that you will then stack to bring out even more detail.Theproblemthatallmountshave(nomatterhowaccuratetheirmotorsare)arethehumansthatoperatethem. WealreadyPolaralignourmountstoenableustocounteractthespinoftheEarthwhichinturnmeansthatwe cantrackanobjectinasingleaxis,rightascension(RA).Thisisokforvisualobservingorshorterexposure lengths,andingeneralaverywellpolaralignedmountcangivebetween1andahalfto2minuteunguided exposuresbeforeyoustarttoseetrailingonthestars.Thisisfinewhenimagingbrightobjectsliketheimpressive OrionNebulabutwhenimagingfainttargetsthenyouneedtoextendyourexposuretimesconsiderably.Andifyou decidetodabbleinnarrowbandimagingthenyoucouldbeneedingsomeseriouslylongexposuresdependanton the camera being used, the only way to achieve this is to implement guiding in to your setup.