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06-01-2014, 11:03 AM   #1
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GPS Astrotracer and aperture

Hi. I have been reading various tutorials about taking night sky photos, and they all say that you will need a lens that has a minimum f-stop number of 2.8. I am assuming that this is because you need to have to shutter open for a little time as possible to let enough light in without the start leaving little trails. Is that correct?

Now I was wondering ...if you use an astrotracer, does that mean that you can use a smaller aperture, and slower shutter since the stars are being followed and the trails won't be an issue? I am looking at buying some lenses for my pentax K-5 and I plan to take night sky photos, and I need to know if the f.2.8 maximum aperture still applies when using the astrotracer?

Thank you in advance!

06-01-2014, 11:44 AM   #2
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The purpose of the astrotracer is to let you use slower shutter speeds. It moves the camera sensor to compensate for the earths movement.
So yes, you can use smaller apertures. Keep in mind that if you have the earth in your shot, you will get earth trails instead of star trails. :P
06-01-2014, 01:33 PM   #3
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A small aperture allows you to have a lower iso. With my 12-24 the smallest aperture is f4, so the other day when shooting non existent meteors I had it set to 15 seconds, f4 and 6400 iso. That would be sensitive enough to capture the short duration of the meteor trail without elongated stars. An f2.4 lens would work at iso 3200. That makes a big difference in noise.
06-01-2014, 02:29 PM   #4
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QuoteOriginally posted by derekkite Quote
A small aperture allows you to have a lower iso.
Do you mean small aperture or low f/number?


Steve

06-01-2014, 03:07 PM   #5
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QuoteOriginally posted by stevebrot Quote
Do you mean small aperture or low f/number?


Steve
Oops, large aperture, small number.
06-01-2014, 03:23 PM   #6
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Ok thanks, that's good advice I can use until get my astrotracer )

Was just really wondering if there were any lens limitations if using an astrotracer. Im guessing the answer is no as you can just leave the shutter open longer. And the focal length obviously need to be fairly wide.

Would anyone recommend the Tamron 17-50 2.8 for night sky?

Thanks.
06-03-2014, 06:56 PM   #7
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Using the Astrotracer, I would recommend shooting at f5.6 and the lowest ISO possible (e.g. ISO 100, 200, or 400). And depending on WHERE you point your camera in the heavens, I find I can generally shoot up to 150 secs (sometimes longer). Longer focal length lenses would have shorter duration perhaps closer to 60 secs or so, so you might have to up the ISO for them.

Michael
06-03-2014, 07:11 PM   #8
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QuoteOriginally posted by derekkite Quote
so the other day when shooting non existent meteors
Glad I wasn't the only one

06-04-2014, 02:55 AM   #9
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QuoteOriginally posted by MJSfoto1956 Quote
Using the Astrotracer, I would recommend shooting at f5.6 and the lowest ISO possible (e.g. ISO 100, 200, or 400). And depending on WHERE you point your camera in the heavens, I find I can generally shoot up to 150 secs (sometimes longer). Longer focal length lenses would have shorter duration perhaps closer to 60 secs or so, so you might have to up the ISO for them.

Michael
Thanks Michael
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