Focus engine for SCT & Edge HD optics. Model 94155-A can be used with the following models:-6 "Schmidt-Cassegrain All models from the year of construction 2006, without off-practice Guider-7" Maksutov-Cassegrain-8, 9.25, 11 and 14 "Schmidt-Cassegrain from construction year 2006-8, 9.25, 11 and 14 "Edge HD All models - Rasa 8" - Rasa 11 "with retrofit set 131231 - Rasa 14" 36cm. Not usable for 5 "SCT and other SCT optics before 2006