 
     
 video.
 video. We have a reducer requiring 86 mm of Optical distance, and we have both a filter wheel
	          and an off-axis guider inserted in the image train between the reducer and the camera. Such devices clearly
	          consume back focus so the thickness of ALL these accessories must be taken into account
	          in calculations. The Image Train Back focus is then the sum of these components
	          thicknesses and back-focus, then as before we use the formula above and subtract the total
	          Image Train Back focus from our Optical Distance.
	          We have a reducer requiring 86 mm of Optical distance, and we have both a filter wheel
	          and an off-axis guider inserted in the image train between the reducer and the camera. Such devices clearly
	          consume back focus so the thickness of ALL these accessories must be taken into account
	          in calculations. The Image Train Back focus is then the sum of these components
	          thicknesses and back-focus, then as before we use the formula above and subtract the total
	          Image Train Back focus from our Optical Distance. ?
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