Learn how to go from unrecognizable raw images from a DSLR camera

To

Milky Way in Cassiopeia

If interested register by contacting Jim Foy or by signing up on the website (registered website members only)

Dates for 2010 astrophotography classes:

Tuesday, January 26 2010 from 7 to 9 PM (Board Room)

Tuesday April 27 2010 from 7 to 9 PM (Board Room)

Tuesday September 21 2010 from 7 to 9 PM (Board Room)

Mark your calendar and plan to attend if you are interested in learning more about astrophotography. The class will be interactive and will start with methods and ideas for using a DSLR camera.

DLSR Class Outline:

Equipment

One shot Camera

• Suitable for Moon, Meteor showers, Sun dog, Moon dog, Aurora, conjunctions, constellation bright stars, etc

• Exposure time <10 sec

DSLR

• Camera choice (Canon or Nikon)

• Main advantages versus one shot is longer exposures (bulb feature), better lens, and more manual control options

• Canon recognizes astrophotography as a use

• Free software for camera control

• Fewer cables needed than Nikon

• If budget allows, purchase camera with live video feed option, which makes focus easier and more reliable than viewing through the lens.

Tripod

• Need for exposures >1/60 sec

• Use for star trails, aurora, planet conjunctions

• Limited to about 5 sec at shortest focal length (18 mm), because of elongated stars

Simple barn door type tracking mount

• Web contains plans for building

• Low cost alternative

Tracking mount

• Increase exposure time to minutes

• Spend time to achieve accurate polar alignment can increase exposures to several minutes

• Autoguide for best star shape

Software

• Control camera

• Digital development processing of photos

Long exposure astrophotography (several minute sub-exposures – use example of Cassiopeia/Milky Way Photo)

• The key difference between daylight photography and astrophotography is signal to noise

• Day light pictures give large signals, which are not significantly effected by defects in the CCD chip and optical train

• Deep sky photography produces images with signals closer to the noise from CCD chip defects

• Light pollution produces gradients

• Optical train clearly visible

• Good news is these can be removed by the use of correction frames and software

Dark frames (example)

• Correction frames (20-30) shot at same time and temperature as light sub-frame with lens cap on and a hood over the lens to ensure total darkness

• Corrects for minor difference between adjacent pixels: some are brighter than others

Bias frames (example)

• Corrects for minor differences across the CCD chip

• Correction frames (20-30) shot at shortest shutter setting at same temperature as light frame with lens cap and hood covering the lens

Flat frames (example)

• Corrects for optical train and dirty optics/CCD chip

• Use light box

• Made light box from battery powered light, translucent plastic sheets, foam filled cardboard and glue

• Correction frames (>4, 20 to 30 better) shot at same focal length, ISO setting and Fstop setting as light frame.

• Expose for time sufficient (5 sec for Nikon D60) to achieve about 50% of maximum camera output (Nikon D60 is 12 bit CCD so maximum is 4056)

Light frame sub-exposures

• Key is to take several (>15) 5 to 10 minute sub exposures of the object

• Correct the frames with bias, darks and flats

• Stack images to give a smoother image with better signal to noise.

Digital processing of photos (example)

• Histogram

• Levels and color balance

• Stretching photo with curves

• Removing gradient (Gradient XTerminator)

• Reducing noise

• Correcting stars

• Sharpening

• Adjust photo appearance-season to taste

If you plan to attend any of the classes please contact me. Depending on interest and progress of the classes, an additional class may be held in December 2010. The classes are free and open to all NSAAC members.