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<blockquote data-quote="BackdoorArts" data-source="post: 625949" data-attributes="member: 9240">One other thing mentioned is aperture and its impact on depth of field. When you zoom in the depth of field narrows, so depending on your distance to subject that subject may go out of focus because your DoF has been reduced. That said, if you look at hyperfocal distances on your lens, at 16mm &amp; f4 you get everything from just over 5ft to Infinity in focus. At 35mm &amp; f4 you get everything from 20ft to Infinity in focus. So, for astrophotography, if your focus is set to anything over 20ft then theoretically you can zoom in and out across the entire focal length without refocusing. My recommendation would be to test that out on a nice day with high clouds and some tree tops in view, and maybe a moon in the daytime sky. Set the focus to somewhere between 20ft and infinity (make sure it's set to manual), and shoot a series of pix at various focal lengths all at f4 (you want to shoot wide open for astrophography). Load 'em onto your computer and pixel peep to your heart's content.</blockquote>

[QUOTE="BackdoorArts, post: 625949, member: 9240"] One other thing mentioned is aperture and its impact on depth of field. When you zoom in the depth of field narrows, so depending on your distance to subject that subject [I]may[/I] go out of focus because your DoF has been reduced. That said, if you look at hyperfocal distances on your lens, at 16mm & f4 you get everything from just over 5ft to Infinity in focus. At 35mm & f4 you get everything from 20ft to Infinity in focus. So, for astrophotography, if your focus is set to anything over 20ft then [B][I]theoretically [/I][/B]you can zoom in and out across the entire focal length without refocusing. My recommendation would be to test that out on a nice day with high clouds and some tree tops in view, and maybe a moon in the daytime sky. Set the focus to somewhere between 20ft and infinity (make sure it's set to manual), and shoot a series of pix at various focal lengths all at f4 (you want to shoot wide open for astrophography). Load 'em onto your computer and pixel peep to your heart's content. [/QUOTE]

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