DSLR for

Astrophotography with a DSLR Camera Alan Erickson Southwest Astrophotography Seminar November 2013 DSLR for . . . DSLR for . . . •  Beginner DSLR for . . . •  Beginner •  Nightscape [copyrighted photo removed] hBp://www.shainblumphoto.com/Astrophotography DSLR for . . . •  Beginner •  Nightscape •  Suburban DSLR for . . . • 
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Beginner Nightscape Suburban Dark Sky Planetary One Shot Color DSLR for . . . • 
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Beginner Nightscape Suburban Dark Sky Planetary One Shot Color Narrowband H-­‐alpha DSLR CMOS vs CCD DSLR CMOS vs CCD Cameras have different design goals. DSLR CMOS vs CCD Cameras have different design goals. •  Low cost •  Low power consumpNon •  Fast read-­‐out DSLR CMOS vs CCD Cameras have different design goals. •  High sensiNvity •  Low cost •  Low power consumpNon •  Low noise •  Dynamic range •  Fast read-­‐out •  Low, repeatable dark current DSLR One Shot Color DSLR One Shot Color Bayer Matrix, aka color filter array DSLR One Shot Color Bayer Matrix, aka color filter array DSLR One Shot Color DSLR Modifica?on DSLR Modifica?on DSLR Modifica?on DSLR Modifica?on DSLR Modifica?on Camera ModificaNon Services •  Gary Honis: ghonis2.ho8.com •  Hap Griffin: www.hapg.org •  Astro Hutech: www.hutech.com DSLR Modifica?on DSLR Modifica?on Signal & Noise Signal & Noise Signal is the light coming from the object and sky background. Signal & Noise Signal is the light coming from the object and sky background. Noise is random variaNons in the recording of the signal and in reading the image from the sensor. Signal & Noise Signal is the light coming from the object and sky background. Noise is random variaNons in the recording of the signal and in reading the image from the sensor. Signal to noise raNo is the most important indicator of image quality. Signal & Noise Three main sources of noise: •  Read noise. Constant. Signal & Noise Three main sources of noise: •  Read noise. Constant. •  Thermal noise. Accumulates during exposure. Signal & Noise Three main sources of noise: •  Read noise. Constant. •  Thermal noise. Accumulates during exposure. •  Shot noise. The square root of the signal. Signal & Noise ISO ISO ISO is a camera se]ng to control the amplificaNon of the image as it is read from the sensor. ISO ISO is a camera se]ng to control the amplificaNon of the image as it is read from the sensor. ISO 800 or 1600 are typically good se]ngs for astro-­‐imaging. ISO ISO is a camera se]ng to control the amplificaNon of the image as it is read from the sensor. ISO 800 or 1600 are typically good se]ngs for astro-­‐imaging. These high ISO se]ngs do not introduce noise. ISO Na?ve ISO se]ngs are the typical numbers 100, 200, 400, 800, 1600, etc. ISO Na?ve ISO se]ngs are the typical numbers 100, 200, 400, 800, 1600, etc. These are implemented as a true amplifier se]ng during read-­‐out. ISO Na?ve ISO se]ngs are the typical numbers 100, 200, 400, 800, 1600, etc. These are implemented as a true amplifier se]ng during read-­‐out. In-­‐between ISO se]ngs such as 160, 320, 640, etc. are computed by the camera a`er converNng the sensor image to digital. These offer no benefit when shooNng in camera raw format. ISO The unity gain ISO is the ISO at which one electron volt corresponds to one digital unit. ISO The unity gain ISO is the ISO at which one electron volt corresponds to one digital unit. The unity gain ISO may not correspond exactly to one of the available ISO se]ngs. ISO The unity gain ISO is the ISO at which one electron volt corresponds to one digital unit. The unity gain ISO may not correspond exactly to one of the available ISO se]ngs. The best ISO se]ngs for astro-­‐imaging will be those nearest the unity gain ISO. ISO Using an ISO se]ng that is too low will lose subtle detail in the image, due to using a range of digital values that is too small. . . ISO ISO Using an ISO se]ng that is too high will sacrifice dynamic range. It will cause unnecessary gaps in the range of digital units used. It may blow out bright features. . . ISO ISO To learn more about unity gain ISO and many other technical aspects of DSLRs, visit Roger N. Clark’s website: clarkvision.com Lenses Lenses Use ~18mm lens for wide field images of the Milky Way and landscape. [copyrighted photo removed] hBp://www.shainblumphoto.com/Astrophotography Lenses Use ~50-­‐80mm lens for capturing constellaNons. Lenses Use ~200-­‐300mm lens for extended objects. Lenses Use f/4 or slower for good edge performance. An excepNonal lens can go faster. Lenses Use f/4 or slower for good edge performance. An excepNonal lens can go faster. Prime lenses tend to perform beBer for the price, compared with zoom lenses. Mounts Mounts For non-­‐tracking exposures, any steady camera tripod will work. [copyrighted image removed] hBp://apod.nasa.gov/apod/ap090909.html Mounts Camera tracking mounts, such as iOptron SkyTracker and Vixen Polarie are good performers, achieving several minutes of good tracking at 200mm focal length. Exposure Exposure For non-­‐tracking exposures, star trailing will limit exposure Nme. [copyrighted photo removed] hBp://www.shainblumphoto.com/Astrophotography Exposure For non-­‐tracking exposures, star trailing will limit exposure Nme. Rule of 600: The maximum Nme in seconds before stars begin to trail noNceably is 600 / focal length. Exposure For tracked exposures, try to expose long enough to raise the sky background well above the margin of read noise. Exposure For tracked exposures, try to expose long enough to raise the sky background well above the margin of read noise. This is indicated by a substanNal margin on the le` side of the histogram. Exposure Use exposure Nme and aperture to achieve this, before resorNng to a higher ISO se]ng. Exposure Under very dark sky condiNons, it may not be possible to raise the histogram this much. Exposure Use a shuBer release device to start the exposure. Some devices have a programmable Nmer for taking a series of shots. Or tether to a laptop to control the camera. Exposure Adding a delay between exposures can let the camera cool a`er the acNvity of image read-­‐out. On the order of 30-­‐60 seconds. Exposure Adding a delay between exposures can let the camera cool a`er the acNvity of image read-­‐out. On the order of 30-­‐60 seconds. Mirror lockup feature can introduce a glow. Test for it on your camera. Avoid it, or use it with the dark frames for consistency. Exposure Adding a delay between exposures can let the camera cool a`er the acNvity of image read-­‐out. On the order of 30-­‐60 seconds. Mirror lockup feature can introduce a glow. Test for it on your camera. Avoid it, or use it with the dark frames for consistency. Turn off the LCD display on the camera to reduce heat and dark current or noise. Acquiring Images Acquiring Images Tethered ShooNng Various astro-­‐imaging applicaNons support DSLR cameras. Backyard EOS is dedicated to Canon DSLRs (Nikon support planned for 2014). Canon EOS UNlity can also be used to focus with Live View and automate the shots. Acquiring Images Acquiring Images Focusing Camera lens infinity mark and auto focus are not reliable for focusing on the sky. Use Live View on a bright star and focus manually, or with Backyard EOS focus controls. Acquiring Images Dithering When taking mulNple exposures for stacking, dithering involves moving the telescope / camera slightly between exposures. Acquiring Images Dithering When taking mulNple exposures for stacking, dithering involves moving the telescope / camera slightly between exposures. This causes the image to be placed at slightly different posiNons on the sensor. Acquiring Images Dithering When taking mulNple exposures for stacking, dithering involves moving the telescope / camera slightly between exposures. This causes the image to be placed at slightly different posiNons on the sensor. Aligning & stacking can then reject sensor defects. Acquiring Images Dithering With a guided mount, dithering can be done automaNcally by so`ware, such as Maxim DL or Backyard EOS with PHD Guide. Acquiring Images Dithering With a guided mount, dithering can be done automaNcally by so`ware, such as Maxim DL or Backyard EOS with PHD Guide. For an unguided mount, adding a geared head, such as the ManfroBo 410 Junior, makes it very easy to tweak the camera direcNon. Acquiring Images Planetary Except for the moon, planetary imaging needs very long focal length of 2000-­‐3000mm (telescope + Barlow). Acquiring Images Planetary Live View and video modes make DSLRs capable planetary imagers. Backyard EOS has a planetary feature that captures video, which can then be imported into Registax. Acquiring Images Acquiring Images Planetary See this arNcle for more info: Jerry Lodriguss, Sky & Telescope May 2012, Planetary Imaging with Your DSLR Camera Filters Filters H-­‐alpha Many nebulae emit strongly in the H-­‐alpha emission line. A modified camera with an H-­‐alpha filter aBached is effecNve at capturing the signal. Filters H-­‐alpha Ideally, the H-­‐alpha image should be extracted directly from the camera raw file, and not run through debayering with the blue and green values. Filters H-­‐alpha The extracted H-­‐alpha exposures can be stacked on their own, and the master scaled up to match the regular RGB image. Filters H-­‐alpha The extracted H-­‐alpha exposures can be stacked on their own, and the master scaled up to match the regular RGB image. Then the H-­‐alpha master can applied as a luminance layer over the RGB image, or blended with the red channel to enhance it. Filters Light PolluNon Suppression Light polluNon is unwanted signal that blankets the scene unevenly, causing gradients. Filters Light PolluNon Suppression Light polluNon is unwanted signal that blankets the scene unevenly, causing gradients. It can limit exposure Nme by overwhelming the sensor with unwanted signal. Filters Light PolluNon Suppression Light polluNon is unwanted signal that blankets the scene unevenly, causing gradients. It can limit exposure Nme by overwhelming the sensor with unwanted signal. Being signal, it contributes to shot noise. Filters Light PolluNon Suppression Light polluNon suppression filters exclude bands of spectrum occupied by street lighNng. Filters Light PolluNon Suppression Light polluNon suppression filters exclude bands of spectrum occupied by street lighNng. With the light polluNon suppressed, exposures can be longer, collecNng more of the wanted signal. Filters Light PolluNon Suppression Light polluNon suppression filters exclude bands of spectrum occupied by street lighNng. With the light polluNon suppressed, exposures can be longer, collecNng more of the wanted signal. A good filter minimizes the impact on color balance. Filters Light PolluNon Suppression Sky glow is an auroral effect caused by ionized atoms in the upper atmosphere. Filters Light PolluNon Suppression Sky glow is an auroral effect caused by ionized atoms in the upper atmosphere. The glow is in specific narrow bands of the spectrum, strongest in green and red. Filters Light PolluNon Suppression Sky glow is an auroral effect caused by ionized atoms in the upper atmosphere. The glow is in specific narrow bands of the spectrum, strongest in green and red. The filter suppresses sky glow as well as light polluNon. Filters Light PolluNon Suppression Filters Light PolluNon Suppression Top brands are IDAS LPS and Astronomik CLS. Filters Light PolluNon Suppression Top brands are IDAS LPS and Astronomik CLS. May not work with wide angle lenses wide open, due to the steepness of the light cone. Filters Diffusion / Fog Brighter stars become larger, making constellaNons more recognizable. [copyrighted image removed] hBp://asterisk.apod.com/viewtopic.php?f=29&t=22079&p=137505&hilit=joshua+bury#p137505 Filters Diffusion / Fog Can hold the filter in front of the lens for just part of the exposure. Experiment. [copyrighted image removed] hBp://asterisk.apod.com/viewtopic.php?f=29&t=22079&p=137505&hilit=joshua+bury#p137505 Processing Processing In-­‐Camera Features Don’t use in-­‐camera features such as noise reducNon or auto dark frame. Processing In-­‐Camera Features Don’t use in-­‐camera features such as noise reducNon or auto dark frame. Noise reducNon can be accomplished to taste later in so`ware and do it as well or beBer. Processing In-­‐Camera Features Don’t use in-­‐camera features such as noise reducNon or auto dark frame. Noise reducNon can be accomplished to taste later in so`ware and do it as well or beBer. Auto dark frame wastes imaging Nme and is mainly mapping out defecNve pixels. Processing CalibraNon The usual calibraNon frames also apply to DSLR imaging: bias, dark, flat. Dark frames need to be made at about the same temperature as the lights. Processing Skipping CalibraNon Good debayering and image processing so`ware may obviate the need for calibraNon. Photoshop with Adobe Camera Raw, and Lightroom are very good at mapping out bad pixels. Processing Skipping CalibraNon Modest noise reducNon can be applied to each subexposure in Adobe Camera Raw or Lightroom, prior to stacking. Processing Skipping CalibraNon Adobe Camera Raw and Lightroom are good at removing vigne]ng, especially for camera lenses. Lightroom has a flat-­‐fielding plug-­‐in available from Adobe. Processing Lightroom Flat-­‐Fielding Processing Lightroom Flat-­‐Fielding Processing Lightroom Flat-­‐Fielding Resources Jerry Lodriguss astropix.com Tony Hallas astrophoto.com digital_astro Yahoo group