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General Photography
Low Light & Night
Star Photography One on One
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<blockquote data-quote="Wahugg" data-source="post: 133617" data-attributes="member: 10685"><p>When you are using a bigger focal length, you are zooming in on the stars, thus their movement is also 'enlarged'. Maybe Dave can explain it better then me, though I can provide an example below.</p><p></p><p><img src="http://i894.photobucket.com/albums/ac148/wahugg/Sharable/4D47E297-8673-4A21-9679-09154B5D90A1-616-0000003CD67B60CF.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p>This image was taken at 18mm and 20 seconds on a Dx sensor. (400/18mm=22.22 theoretical max exposure time) Since I fall under 22 seconds, there is no noticeable star streaks. However if I were to zoom in on the picture, simulating a bigger focal length, star steaks become noticeable because your making the stars bigger.</p><p></p><p><img src="http://i894.photobucket.com/albums/ac148/wahugg/Sharable/ex.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p>This is the same image above, but I zoomed in on the star field in the middle. See the streaks? The streaks have only become noticeable because of the simulated larger focal length.</p><p></p><p>-Wahugg</p><p></p><p>Edit:</p><p></p><p>Originally when I was doing research on night photography, I kept on seeing a reference to the Rule of 600. The Rule of 600 is the formula (600/focal length = theoretical max exposure time). I found this formula to be inaccurate for me and I later figured it was so inaccurate due to my cameras having crop sensors. So I simply took 600, divided it by the 1.5x crop factor of the Nikon DX sensor, and got 400. Thus the Rule of 600 is for FX, and the Rule of 400 is for DX.</p></blockquote><p></p>
[QUOTE="Wahugg, post: 133617, member: 10685"] When you are using a bigger focal length, you are zooming in on the stars, thus their movement is also 'enlarged'. Maybe Dave can explain it better then me, though I can provide an example below. [IMG]http://i894.photobucket.com/albums/ac148/wahugg/Sharable/4D47E297-8673-4A21-9679-09154B5D90A1-616-0000003CD67B60CF.jpg[/IMG] This image was taken at 18mm and 20 seconds on a Dx sensor. (400/18mm=22.22 theoretical max exposure time) Since I fall under 22 seconds, there is no noticeable star streaks. However if I were to zoom in on the picture, simulating a bigger focal length, star steaks become noticeable because your making the stars bigger. [IMG]http://i894.photobucket.com/albums/ac148/wahugg/Sharable/ex.jpg[/IMG] This is the same image above, but I zoomed in on the star field in the middle. See the streaks? The streaks have only become noticeable because of the simulated larger focal length. -Wahugg Edit: Originally when I was doing research on night photography, I kept on seeing a reference to the Rule of 600. The Rule of 600 is the formula (600/focal length = theoretical max exposure time). I found this formula to be inaccurate for me and I later figured it was so inaccurate due to my cameras having crop sensors. So I simply took 600, divided it by the 1.5x crop factor of the Nikon DX sensor, and got 400. Thus the Rule of 600 is for FX, and the Rule of 400 is for DX. [/QUOTE]
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