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11-13-2013, 07:24 PM   #1

Join Date: Dec 2011
Location: Nevada
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Yet another night sky question.

All the night sky stuff I've read says shoot wide open. I have a number of lenses, Rokinon 8mm. Sears 50mm 1.7, Sears 50mm 1.4, Pentax DAL 18-55mm. All seem to sharpen up when stopped down, So, wide open or bump the ISO?

11-13-2013, 10:19 PM   #2
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Join Date: Mar 2008
Location: Prince George, BC
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Depends how and why you are shooting. If just a fixed lens on a tripod with no tracking and you wish to capture stars as individual points then keeping the lens as wide open as possible will help keep the exposure time down. If using tracking such as the O-GPS1 unit from Pentax then you are able to stop down the lens a bit if you so wish. An equatorial tracking mount will allow you to stop down even more. The main reason to stop down is to shoot in the sweet spot of the lens away from deficiencies such as vignetting and to gain a bit of sharpness. It should be noted that the new K-3's processing is so fast that it is now feasible to turn on in-camera lens corrections during astrophotography. If doing star trails where you will potentially be doing long exposures then the smaller the aperture, the narrower the star trail will be.


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