Ansel Adams Wilderness Astro Landscape

Started Sep 24, 2017 | Discussions thread
OP Wayno Regular Member • Posts: 405
Re: Ansel Adams Wilderness Astro Landscape

MacUser2 wrote:

Contrary to what is written on a great many web sites, the crop factor must never be used in calculating the exposure time. The crop factor does not actually change the focal length, it is equivalent to opening an image in Lightroom and then cropping it.

The only physical parameters that should be considered are the pixel pitch, the focal length of the lens and the declination of the star(s). The photographic astronomers developed an equation to calculate the best exposure time (The Plate Scale Equation) which can be applied to determine the time for a point of light to transit from one pixel to the next pixel. In your case this is 3.4 seconds for a star on the celestial equator. Generally, you can push your exposure time to 2 to 3 times this value.

The Rules of 600, 500, 400, 300, etc are only approximations. Roger Clark recommends using the Rule of 200, it is much better, but it still is only an approximation because it does not consider the pixel pitch or the declination. But it will produce much better results than the other "Rules".

Putting all the tech talk aside, I really admire your photograph.

Thank you for your knowledgeable response -- really appreciate the information.

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