Tyler, Just WOW! Have a list of questions, perhaps they will get answered at the meeting. How accurately are you polar aligned versus exposure length? Is the G11 still set up each session or do you now have a fixed position? What were the exposures? My DSLR can take darks and do the subtraction itself is that adequate or should I not use that feature and take a separate dark set? Lot more questions but I'll wait. In awe, Steve
Steve and Jim, I will try to answer some of your questions in this email. I image from my back yard patio and start from scratch each time. I carefully align the Losmandy G-11 each time, using the polar alignment scope, which gets me close enough that alignment is rarely an issue in my images. I never take the time to do a drift alignment. When I get an observatory built (this spring I hope), I will take the time to get the mount perfectly aligned, but I just don't think it matters all that much when autoguiding at the focal lengths I use. The alignment needs to be close, but not perfect. The horsehead is a bright object, so I didn't need to collect massive amounts of data to get a decent image. This shot includes: 45 minutes of luminance data - 9x5 min subs - unbinned 20 minutes each of RGB data - 4x5 min subs - binned 2x2 That's it. I didn't use any darks on this data, but used flats to even out the field and remove the dust donuts. I tried using CCDStack to combine the frames and preprocess. I was quite happy with the result. It has a data rejection feature that is really effective at removing hot and cold pixels. Don't get the wrong idea about dark frames. I nearly always use them. But I tried the data rejection this time and it worked out OK. I have read that using a single dark frame can actually introduce noise rather than diminish it. My guess is that a series of dark frames may work better. But, the noise varies greatly with sensor temperature, which is not selectable on a DSLR. You may need to experiment with the DSLR to see what works best. On my Nikons, the dark subtraction is done after the image is collected, effectively doubling the time it takes to get a single exposure. I would be tempted to try collecting a single dark frame to use later, and then spend more time collecting photons from the target object. I think spending half of your imaging time collecting dark frames is a mistake. On another issue... I always "dither" using the autoguider, which makes processing much easier. Dithering moves the scope slightly between frames so that hot and cold pixels on the chip move relative to the object being photographed. That way, the defects don't line up. They are easier to identify and remove using automated methods like median or sigma combine. I hope some of this is helpful to someone. Cheers, Tyler
Very helpful, Tyler. I have one more question: I haven't tried dithering yet but I intend to. Do you have to pause between photos to reacquire a guide star? Many thanks, Joe --- On Sun, 2/8/09, Tyler Allred <tylerallred@earthlink.net> wrote: From: Tyler Allred <tylerallred@earthlink.net> Subject: Re: [Utah-astronomy] Horsehead and Flame To: "'Utah Astronomy'" <utah-astronomy@mailman.xmission.com> Date: Sunday, February 8, 2009, 9:03 AM Steve and Jim, I will try to answer some of your questions in this email. I image from my back yard patio and start from scratch each time. I carefully align the Losmandy G-11 each time, using the polar alignment scope, which gets me close enough that alignment is rarely an issue in my images. I never take the time to do a drift alignment. When I get an observatory built (this spring I hope), I will take the time to get the mount perfectly aligned, but I just don't think it matters all that much when autoguiding at the focal lengths I use. The alignment needs to be close, but not perfect. The horsehead is a bright object, so I didn't need to collect massive amounts of data to get a decent image. This shot includes: 45 minutes of luminance data - 9x5 min subs - unbinned 20 minutes each of RGB data - 4x5 min subs - binned 2x2 That's it. I didn't use any darks on this data, but used flats to even out the field and remove the dust donuts. I tried using CCDStack to combine the frames and preprocess. I was quite happy with the result. It has a data rejection feature that is really effective at removing hot and cold pixels. Don't get the wrong idea about dark frames. I nearly always use them. But I tried the data rejection this time and it worked out OK. I have read that using a single dark frame can actually introduce noise rather than diminish it. My guess is that a series of dark frames may work better. But, the noise varies greatly with sensor temperature, which is not selectable on a DSLR. You may need to experiment with the DSLR to see what works best. On my Nikons, the dark subtraction is done after the image is collected, effectively doubling the time it takes to get a single exposure. I would be tempted to try collecting a single dark frame to use later, and then spend more time collecting photons from the target object. I think spending half of your imaging time collecting dark frames is a mistake. On another issue... I always "dither" using the autoguider, which makes processing much easier. Dithering moves the scope slightly between frames so that hot and cold pixels on the chip move relative to the object being photographed. That way, the defects don't line up. They are easier to identify and remove using automated methods like median or sigma combine. I hope some of this is helpful to someone. Cheers, Tyler _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://gallery.utahastronomy.com Visit the Wiki: http://www.utahastronomy.com
Joe, One of the things I like about using MaxIm DL to collect the data is that it will dither for you. You can set a limit for the number of pixels it can move, and it randomly moves the guide star on the chip by a few pixels between each frame. I'm sure that many other software packages will do the same. Tyler PS - I should be careful about offering advice about imaging with DSLR's because that is not what I do. Even using a color astro camera requires somewhat different processing steps. There are many people who are experts at DSLR imaging. I should send people their way for "Real" advice. Bye. _____________________________________________ -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Joe Bauman Sent: Sunday, February 08, 2009 10:19 AM To: Utah Astronomy Subject: Re: [Utah-astronomy] Horsehead and Flame Very helpful, Tyler. I have one more question: I haven't tried dithering yet but I intend to. Do you have to pause between photos to reacquire a guide star? Many thanks, Joe --- On Sun, 2/8/09, Tyler Allred <tylerallred@earthlink.net> wrote: From: Tyler Allred <tylerallred@earthlink.net> Subject: Re: [Utah-astronomy] Horsehead and Flame To: "'Utah Astronomy'" <utah-astronomy@mailman.xmission.com> Date: Sunday, February 8, 2009, 9:03 AM Steve and Jim, I will try to answer some of your questions in this email. I image from my back yard patio and start from scratch each time. I carefully align the Losmandy G-11 each time, using the polar alignment scope, which gets me close enough that alignment is rarely an issue in my images. I never take the time to do a drift alignment. When I get an observatory built (this spring I hope), I will take the time to get the mount perfectly aligned, but I just don't think it matters all that much when autoguiding at the focal lengths I use. The alignment needs to be close, but not perfect. The horsehead is a bright object, so I didn't need to collect massive amounts of data to get a decent image. This shot includes: 45 minutes of luminance data - 9x5 min subs - unbinned 20 minutes each of RGB data - 4x5 min subs - binned 2x2 That's it. I didn't use any darks on this data, but used flats to even out the field and remove the dust donuts. I tried using CCDStack to combine the frames and preprocess. I was quite happy with the result. It has a data rejection feature that is really effective at removing hot and cold pixels. Don't get the wrong idea about dark frames. I nearly always use them. But I tried the data rejection this time and it worked out OK. I have read that using a single dark frame can actually introduce noise rather than diminish it. My guess is that a series of dark frames may work better. But, the noise varies greatly with sensor temperature, which is not selectable on a DSLR. You may need to experiment with the DSLR to see what works best. On my Nikons, the dark subtraction is done after the image is collected, effectively doubling the time it takes to get a single exposure. I would be tempted to try collecting a single dark frame to use later, and then spend more time collecting photons from the target object. I think spending half of your imaging time collecting dark frames is a mistake. On another issue... I always "dither" using the autoguider, which makes processing much easier. Dithering moves the scope slightly between frames so that hot and cold pixels on the chip move relative to the object being photographed. That way, the defects don't line up. They are easier to identify and remove using automated methods like median or sigma combine. I hope some of this is helpful to someone. Cheers, Tyler _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://gallery.utahastronomy.com Visit the Wiki: http://www.utahastronomy.com _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://gallery.utahastronomy.com Visit the Wiki: http://www.utahastronomy.com
To All. By way of clarification on the earlier post.... that exposure info should have read as follows... *** 45 minutes of luminance data - 9x5 min subs - unbinned and *** 20 minutes each of RGB data - 4x5 min subs - binned 2x2. The exposure lines ran together when I viewed the message. Cheers, Tyler _____________________________________________ -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Tyler Allred Sent: Sunday, February 08, 2009 9:04 AM To: 'Utah Astronomy' Subject: Re: [Utah-astronomy] Horsehead and Flame Steve and Jim, I will try to answer some of your questions in this email. I image from my back yard patio and start from scratch each time. I carefully align the Losmandy G-11 each time, using the polar alignment scope, which gets me close enough that alignment is rarely an issue in my images. I never take the time to do a drift alignment. When I get an observatory built (this spring I hope), I will take the time to get the mount perfectly aligned, but I just don't think it matters all that much when autoguiding at the focal lengths I use. The alignment needs to be close, but not perfect. The horsehead is a bright object, so I didn't need to collect massive amounts of data to get a decent image. This shot includes: 45 minutes of luminance data - 9x5 min subs - unbinned 20 minutes each of RGB data - 4x5 min subs - binned 2x2 That's it. I didn't use any darks on this data, but used flats to even out the field and remove the dust donuts. I tried using CCDStack to combine the frames and preprocess. I was quite happy with the result. It has a data rejection feature that is really effective at removing hot and cold pixels. Don't get the wrong idea about dark frames. I nearly always use them. But I tried the data rejection this time and it worked out OK. I have read that using a single dark frame can actually introduce noise rather than diminish it. My guess is that a series of dark frames may work better. But, the noise varies greatly with sensor temperature, which is not selectable on a DSLR. You may need to experiment with the DSLR to see what works best. On my Nikons, the dark subtraction is done after the image is collected, effectively doubling the time it takes to get a single exposure. I would be tempted to try collecting a single dark frame to use later, and then spend more time collecting photons from the target object. I think spending half of your imaging time collecting dark frames is a mistake. On another issue... I always "dither" using the autoguider, which makes processing much easier. Dithering moves the scope slightly between frames so that hot and cold pixels on the chip move relative to the object being photographed. That way, the defects don't line up. They are easier to identify and remove using automated methods like median or sigma combine. I hope some of this is helpful to someone. Cheers, Tyler _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://gallery.utahastronomy.com Visit the Wiki: http://www.utahastronomy.com
Hi all, I'll do my best to let you know each Friday what I blogged about over the past week. Here's today's: This past week in the Trib's Astronomy Blog: Traffic cops in space? When satellites collide. One Small Step. Neutron star takes center stage. Protecting the Night Sky. http://blogs.sltrib.com/frontier Comments always welcome. Thanks for reading! Sheena McFarland State Government Reporter The Salt Lake Tribune 90 S. 400 West, Suite 700 Salt Lake City, UT 84101 Office: (801) 257-8619 Cell: (801) 510-5567 Fax: (801) 257-8525 smcfarland@sltrib.com
participants (4)
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Joe Bauman -
Sheena McFarland -
Stephen Peterson -
Tyler Allred