2Why is Guiding Required? If you follow a star with your telescope at high magnification, you will probably notice that the position of the star changes in the field of view of your eyepiece.
3What Causes Star Drift ? Star drift is caused by three main factors: A poor polar alignment - which causes a slow drift and a slow rotation of the star in the field of view.Periodic error in the mount’s tracking rate - this error results from a worm gear.Random errors - caused by dirt, dents and variations in the drives gear train. If these random errors are large and fast enough, they can make unguided exposures impossible.
4Fixing Problem Mounts. Align your mount with the NCP. Periodic Errors Random Errors
5How to correct for this drift. Off-Axis GuiderGuide ScopeGuiding EyepieceManual GuidingAuto guiderSelf guider
6Off-Axis GuiderFor Beginners, the OFF-AXIS GUIDER is a major life saver. A novice is immediately capable of getting some great photos without having to deal with the flexure problems that are sometimes inherent when one uses a separate guide scope.
10Off-Axis Guider Pro’s Con’s Easy setup. Simple design. No tube flexure or sag.Eliminates mirror shift problems.Con’sWill not find a suitable guide star of all objects.Will need to guide from various positions.Harder to frame objects.
11Guide Scope A second telescope which is used A second telescope which is usedto guide the main telescopeduring an imaging or photographicsession.Guide scopes must be at least ½ theEFL of the main imaging scope forCCD work and at least 2.5x thephotographic power of the mainphotographic scope for manualguiding.
12Guide Scope Guidelines Contrary to popular opinion, guiding with a guide scope is no more difficult or complicated than using an off-axis guider if one follows a few simple rules.The most fundamental mistake is to attempt to mount the guide scope directly to the primary tube. A guide scope is just too heavy and will bend the main tube in all sorts of random ways when in use.The most convenient way to mount the guide scope is with a set of adjustable rings. These must however, be attached to the mounting in some direct way that will not influence or be influenced by the primary telescope.
13Guide Scope Pro’s Con’s Possible tube flexure or sag. Easy setup. Easier framing of main object.Better guide star symmetry.Con’sPossible tube flexure or sag.Possible mirror shift with SCT’s.Requires the purchase of an additional scope and mounting rings.Guide stars will be dimmer.
14Guiding Eyepiece Guiding eyepieces offer a myriad of options: Single set of crosshairsDual crosshairsTarget style reticlesDiopter adjustment for crosshairsVariable illuminationBlinking illuminationWireless batteryMulticolor optionsMovable reticles
18Self GuiderIntegrated imaging and auto guiding using a single CCD camera with a built-in auto guider like the SBIG ST7, ST8 and ST9 cameras or a CCD which can download a part of the image without deleting all the pixels, like the Starlight-Xpress MX series.
19Auto Guider Alignment Before starting any kind of guided exposure, it is highlyrecommended that the trackingCCD is aligned with the axisof the telescope so that motionsin R.A. and DEC. cause theguide star to move parallel tothe CCD array.
21How to Select a Guide Star? The star must be at least 1000 ADU’s over the sky background.The star must not exceed 50% of the detectors saturation point.Saturation point = 50 * (well depth / gain)The selected guide star must be the brightest star in the detector field.
22Adjusting Calibration Times Focal Length (mm)Suggested Calibration Time (Seconds)30201074
23Camera/Telescope Combination Formula Arcseconds/pixel = 206*(F.L. in mm / pixel size in microns)