Wednesday, 22 February 2017

depth of field - Why should I use the widest aperture for star photography?



In the article, Photographing Stars Using a Kit Lens, the author talks about keeping the widest aperture, e.g. ƒ/3.5. But it's my understanding that a wide aperture means a smaller area will be in focus. I want to capture the whole sky, so ideally it should be ƒ/16 or ƒ/22, correct?


I tried ƒ/3.5 and it worked like a charm.


So, can anybody please put a light on this? What exactly is going on here?



Answer



Even though the distance of various stars from your camera on Earth can vary by astronomical distances, they are all far enough away that the light from them enters your lens as collimated rays. This means you don't need much depth of field because the lens must be focused to precisely infinity for any and all of them to be in sharpest focus.


The reason the wider aperture can help is because it allows more light through and that in turn allows a faster shutter speed for the same exposure value/allows collecting more light in the same amount of time. If your camera is stationary this allows you to capture dimmer stars without creating star trails.


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