Using Dark Frame sUbtraction To compensate for the lack of in-camera noise reduction, you can take one extra frame at the end of the sequence; it should have the same exposure length, the lens cap on the lens, and the eyepiece covered. This dark frame can be used for manual dark frame subtraction in postprocessing. This image will be used only as a backup in the event that your RAW file converter does not do an adequate job removing noise in your images. When you process your images along with this extra frame, you can follow the procedure outlined with one major change. Set only the white balance and make no other adjustment to your RAW files. Make sure sharpening and noise reduction are turned off. Aside from the white balance, all adjustments must be made to the final rendered and flattened file. Place the dark frame on top of the stack, set the blending mode of this layer only to Difference, and adjust the opacity to achieve the best effect. Start at 50% opacity and increase as needed. Dark frame subtraction or calibration works by removing any fixed pattern noise created by the sensor during long exposures. Random noise, which is more of a factor at high-ISO settings, will not be removed using this technique. Other Stacking Options · Dr.Brown'sStack-A-Matic-APhotoshopscriptforMacandWindows.Free.Arevised versionofStack-A-Maticspecificallydesignedforstartrailimagesisnowavailable. Unlikepreviousversions,V2.0.6andnewerdoesnotrequirePhotoshopExtended,doesnot automaticallyconvertthestackedfiletoasmartobject.Itdoes"stackaslayers"and"set blendingmodetolighten"bydefault,andthereisevenanoptiontomakeitcreatelayer night photography masksforeachlayer,facilitatingtheuseofonlypartsofalayer.ScottMartinusedStack- A-MaticonhisTexasLoveBusphotograph.Thisisnowthepreferredmethodforimage stacking. · · http://www.russellbrown.com/scripts.html Startrails.exe-Thisisaneasytousefreewareprogram,butisunfortunatelyonly compatiblewithWindows.ShawnPetersonuseditforhisBodieWheelofWonderimage. http://www.startrails.de/html/software.html Keith'sImageStacker-Designedforastronomicalimagesshotthroughatelescope,but worksforstartrailsaswell.Ithasmanyuserdefinedcontrols,andmoredifficulttouse thantheothermethods.It'sfortheMaconly,andafifteendollardonationisrequested. http://keithwiley.com/software/keithsImageStacker.shtml 216