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04-17-2016, 05:53 AM   #991
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QuoteOriginally posted by colonel00 Quote
Yeah, I get that they are brighter but that shouldn't actually make them larger, should it? Perhaps it was part of your PP that caused this result?
Stars are point-like sources of light, but photograps of these are not 'points'. They are images of diffraction patterns, consisting of concentric bright and dark circles whith a diameter that depends upon the absolute aperture (size of entrance pupil) and focal length of your optics. The larger the f-number, the larger the image of the diffraction pattern.

The bright circles decrease rapidly in brightness with the distance from the center, and we often only capture the innermost central part, but he brighter the star, the more of this diffraction pattern you may/will actually capture.


Last edited by Stone G.; 04-17-2016 at 06:17 AM.
04-17-2016, 11:54 AM   #992
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QuoteOriginally posted by Stone G. Quote
Stars are point-like sources of light, but photograps of these are not 'points'. They are images of diffraction patterns, consisting of concentric bright and dark circles whith a diameter that depends upon the absolute aperture (size of entrance pupil) and focal length of your optics. The larger the f-number, the larger the image of the diffraction pattern.

The bright circles decrease rapidly in brightness with the distance from the center, and we often only capture the innermost central part, but he brighter the star, the more of this diffraction pattern you may/will actually capture.
Beside the diffraction paterns, the atmosphere is not a steady medium. Air is circulating in many directions, depending of altitude, and the light pass is nothing like a perfectly straight line. Also, there is dust, ice cristals, and these gases, with different refraction index, which make the light to bend and scatter even more. Anyone can see the star twinkling with his eyes, and this is a result of all these phenomena.

In a long exposure, this twinkle are translated in movements of the stars images in any direction, all recorded by the camera, and finally forming a round ball of light, bigger or smaller, depending on the luminosity of the star. You can clearly see that the bigger star twinkle much more than the small ones. That's because the scattered light from the small stars is to little for the eye, or the sensor, to give a circle of the same size.

Last edited by JimmyDranox; 04-17-2016 at 12:00 PM.
04-18-2016, 05:06 AM   #993
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QuoteOriginally posted by JimmyDranox Quote
In a long exposure, this twinkle are translated in movements of the stars images in any direction, all recorded by the camera, and finally forming a round ball of light, bigger or smaller, depending on the luminosity of the star.

True; less than perfect seeing will smear out and distort objects in the sky - both visually and photographically. This is the rationale behind adaptive optics. But even in empty space, with a large aperture telescope you will find that brighter stars forms larger images, as this Hubble image demonstrates:


Hubble Space Telescope Images | NASA
04-20-2016, 09:40 AM   #994
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Question for those with experience using the GPS tracker with their camera's. If you're using the astro tracker (or what ever the correct name is), is it only used for stars, or can it also be used for planets and the moon?

04-20-2016, 11:04 AM - 1 Like   #995
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QuoteOriginally posted by eccs19 Quote
Question for those with experience using the GPS tracker with their camera's. If you're using the astro tracker (or what ever the correct name is), is it only used for stars, or can it also be used for planets and the moon?
For acceptable images of the planets you need a large telescope or at least an extreme tele lens. For both the Astrotracer is not useful and other techniques apply much better (e.g. webcam and telescope) Furthermore e.g. Jupiter is so bright that you do not need a tracker. Also the brightness the moon leads to exposure times that make Astrotracer unnecessary.
04-20-2016, 12:34 PM   #996
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QuoteOriginally posted by Pete_XL Quote
For acceptable images of the planets you need a large telescope or at least an extreme tele lens. For both the Astrotracer is not useful and other techniques apply much better (e.g. webcam and telescope) Furthermore e.g. Jupiter is so bright that you do not need a tracker. Also the brightness the moon leads to exposure times that make Astrotracer unnecessary.
Perfect. Thanks for the information. Greatly appreciated.
04-20-2016, 03:34 PM - 1 Like   #997
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QuoteOriginally posted by eccs19 Quote
is it only used for stars, or can it also be used for planets and the moon?
personally I use only for stars......however I was surprised that Sagitta had used his during one of the eclipses (ferget if solar or lunar) but it made sense that a much longer than usual exposure time was needed and as I recall he did a very nice series of the event........I would tag him to explain but do not know how
04-23-2016, 07:03 PM - 4 Likes   #998
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Great Orion Nebula I shot a couple of months ago. I stacked 60 shots of 30 second exposures at ISO 80. I attached my K-5 at prime focus to a Skywatcher Maksutov-Newtonian 190mm telescope with a mount tracking the rotation of the earth assisted with an autoguider. Used Deep Sky Stacker to add all exposures together, and photoshop and Oloneo for final processing.

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04-24-2016, 01:57 AM   #999
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QuoteOriginally posted by Eric Seavey Quote
Great Orion Nebula I shot a couple of months ago. I stacked 60 shots of 30 second exposures at ISO 80. I attached my K-5 at prime focus to a Skywatcher Maksutov-Newtonian 190mm telescope with a mount tracking the rotation of the earth assisted with an autoguider. Used Deep Sky Stacker to add all exposures together, and photoshop and Oloneo for final processing.

Very nice result! You managed to cover the whole dynamic range of the nebula from the faitest parts to the extreme bright trapezum star region! Did you use different luminance layer masking in Photoshop or any HDR technique or is it all "from the sensor".


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04-24-2016, 08:10 AM   #1000
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QuoteOriginally posted by Eric Seavey Quote
Great Orion Nebula
amazing! wonderful job
04-24-2016, 08:57 AM   #1001
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QuoteOriginally posted by Pete_XL Quote
Very nice result! You managed to cover the whole dynamic range of the nebula from the faitest parts to the extreme bright trapezum star region! Did you use different luminance layer masking in Photoshop or any HDR technique or is it all "from the sensor".


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Pete/Aaron,
Thanks! All exposures were 30 seconds. However, by stacking them, the noise gets really low, and I am able to extract the faint parts with a very steep S-curve in DDS without blowing out the stars. I used Oloneo to tonemap the 16-bit image and pull out more contrast.
08-26-2016, 06:48 PM - 1 Like   #1002
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The Pentax K-5 is definitely a great camera for astro photography! Here I shot the Trifid (with M21 in the corner) and the Lagoon Nebula.
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08-27-2016, 12:16 AM   #1003
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QuoteOriginally posted by Eric Seavey Quote
The Pentax K-5 is definitely a great camera for astro photography! Here I shot the Trifid (with M21 in the corner) and the Lagoon Nebula.
WOW! Lots of kudos!
What setup besides the K5 did you use?


Regards, Pete
08-30-2016, 07:03 PM   #1004
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Beautiful capture of the Triffid and the Lagoon.
08-31-2016, 03:25 PM - 1 Like   #1005
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QuoteOriginally posted by Stone G. Quote
Thank you dqniel,

I believe that my best answer will be to direct you to my page with Astrotracer sample images:

DSLR Astophotography: Astrotracer Images with Pentax GPS Unit O-GPS1

On the more general level, I also have this page on camera settings to refer to:

Camera Settings for Astrophotography

Good luck - and have fun!
Amazing group of shots. Inspiring!
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