Celestron CGE1100 Telescope, Standard, With Fastar, Model, Cassegrain f/10, Reducer/Corrector

Figure 7-3

Fastar L ens Assem bl

CCD Camera

Figure 7-4

The key factors for good CCD imaging are; exposure time, field-of-view, image size, and pixel resolution. As the F/# goes down (or gets faster), the exposure times needed decreases, the field-of-view-increases, but the image scale of the object gets smaller. What is the difference between f/2 and f/10? F/2 has 1/5 the focal length of f/10. That makes the exposure time needed about 25 times shorter than at f/10, the field of view 5 times larger and the object size 1/5 compared to that of f/10. (see Table below)

	Telescope	Standard	With	With Fastar
	Model	Cassegrain f/10	Reducer/Corrector	Lens Accessory
			f/6.3	f/2
Focal	CGE 800	80" (2032mm)	50.4" (1280mm)	16" (406.4mm)
	CGE 1100	110" (2800mm)	69.5" (1764mm)	23.1 (587mm)
Length &
Speed
	CGE 1400	154" (3910mm)	88.2" (2239mm)	29.4" (746mm)
	CGE 800	8 x 6.1 (arc	12.6 x 9.7 (arc min)	40 x 30 (arc
		min)		min)
ST 237
	CGE 1100	5.8 x 4.4 (arc	9.2 x 7.0 (arc min)	28 x 21 (arc
F.O.V.*		min)		min)
	CGE 1400	4 x 3 (arc min)	7 x 5.5 (arc min)	22 x 17 (arc
				min)

*Field of view calculated using SBIG ST 237 CCD camera with 4.7mm x 3.6mm chip.

Table 7-3

The following is a brief description of the advantages of imaging at each f-number configuration and the proper equipment needed to use the telescope in any of its many settings

Fastar F/2 Imaging

As stated above, the exposure times are much shorter at f/2 than at f/6.3 or f/10. The field-of-view is wider, so it is easier to find and center objects. Also with a wider field-of-view you can fit larger objects (such as M51, The Whirlpool Galaxy) in the frame. Typical exposure times can be 20-30 seconds for many objects. Under dark skies you can get an excellent image of the Dumbbell Nebula (M27) with only a few 30 second exposures (see figure 8-5 below). The spiral arms of the Whirlpool galaxy (Figure 8-6) can be captured

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