Mississauga Centre RASC

86th Meeting

                                                                                                Members’ Night       

Day:                Friday June 8, 2007

Chair:                Terry Hardman

Speakers:            Randy Attwood 

                          William Callahan 

Introduction to Astrophotography

Randy Attwood presented a talk about astrophotography, an extensive topic about equipment, exposures, wide angle sky shots of constellations, and the challenge of shooting through a telescope; computers, webcams and CCD cameras.  Astrophotography is rewarding and one can use simple equipment to begin with.  One needs patience and practice. 

To get started, consider film vs. digital, SLR or point-and-shoot.  A tripod is necessary for exposures of several seconds, as is a cable release for wide angle shots of constellations, the Moon, and conjunctions.  Light pollution is a challenge. There may be a problem focusing to infinity.  With a digital camera, the result can be seen immediately as opposed to film.  Randy showed create use images of star trails which appear after 30 seconds as well as fogging from light pollution.  For longer exposures, use a barn door tracker, piggybacking on a telescope, or an illuminated reticle for very good pictures.  Computer enhancement of digital images is done with Registax or Adobe Photoshop. 

More advanced is photography through the telescope with an attachment or the afocal method.  Turbulence in the atmosphere can create problems. The effect of rotation of the Earth is multiplied.  To get over these problems, webcams can be used and individual frames selected.  A digital SLR can be attached to the telescope.  Deep sky imaging needs longer exposures and  accurate guiding through a second telescope or off-axis using a CCD guider. 

In review, decide what to use, consider a digital SLR, buy a telescope which fits astrophotography.  Books, magazines, websites , yahoo groups, Starfest etc. are all good resources.

Collimation of Telescopes

William Callahan described the collimation of telescopes.  Collimation is the is the process of aligning the optical components of a telescope in order to get the best performance out of a telescope. It is especially critical for high magnification viewing (planets) to give contrast.  Every telescope needs to be collimated, but Newtonians and reflectors should have this done every time.  

The very first time, there is often confusion because of the many circles within circles that are seen.  The optical tube should be horizontal so as not to drop objects onto the primary mirror.  Screws should turn freely. The first time, collimation should be done in the daylight.  A Cheshire and sight tube are the only optical tools needed but a laser is useful although it has its limitations.

For a Newtonian, the secondary mirror is first centered and rotated so that it looks round and its centre is pointed at the centre of the primary.  The optical axis of the primary is then centered onto the secondary using the Cheshire or laser. Steps are repeated until all parts are aligned.  Once the first steps are complete, they will not have to be repeated very often. Only the primary mirror alignment is done every time the telescope is set up. For a SCT and refractor, an artificial star and high power eyepiece are used.

References:                                                      www.skyandtelescope.com/howto/diy/3306876.html  

  (best site) www.catseyecollimation.com/mccluney.htm                                      

   www.backyardastronomy.com/appendix/cleaning.pdf 

Observing

Randy Attwood mentioned that the Space Shuttle had gone up. Heavens.com website shows the location of the shuttle and ISS. The best chance to see both is at the undocking around June 17.  

An observing committee has been formed with William Callahan as chair and Vic Cooper and bob Anderson as members.  A survey is being carried out to find what people are observing.

William spoke about observing and asked the membership to complete the survey. It is necessary to become part of the yahoo group because this is the was to communicate among the members.

Randy said that people join the club in order to observe  and we intend to set up observing sessions. He also discussed the upcoming Starfest weekend.

Submitted by Chris Malicki, Secretary  Chris Malicki, Secretary                               back to Miss Centre. meeting reports page
Mississauga Centre RASC