| 31. | Astronomers such as Johannes Hevelius were constructing telescopes with focal lengths as long as.
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| 32. | What is its focal length range for the zoom feature?
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| 33. | It also removes the need to have separate viewfinders for different lens focal lengths.
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| 34. | You need the focal length of the lens in use.
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| 35. | It had a diameter, focal length speculum metal objective mirror.
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| 36. | Optical zoom is actual magnification that shows true focal length.
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| 37. | This becomes more problematic with short focal length telescopes which require larger secondary mirrors.
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| 38. | Both the and Newtonian reflectors were F5 in focal length.
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| 39. | The focal length f is considered negative for concave lenses.
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| 40. | The distance from the mirror to the focal plane is called the focal length.
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