Posts Made By: Dean Ketelsen

Hi All-
I thought you might be interested in seeing the result of this sequence I took from the picnic area of Kitt Peak National Observatory. Photos were taken every 2 minutes - from 1/1000 second while the sun was still up to a max of 40 seconds once it got dark. Tripod-mounted Canon 20Da taken with zoom set to about 35mm at F/4.5. Kind of a big file at 7.6 Meg...

http://alice.as.arizona.edu/~ketelsen/KPNO.gif

-Dean

Always my favorite at Whitewater Draw, AZ, though most go for the 17,000 cranes making a racket in the background. This little guy always seems to be around, this time just before sunset
-Dean

Hi Justin-

I'm betting you shot that pic with a UV or clear filter of some sort, right? If so, the "comet" is likely a reflection off the filter from the bright star Vega. Imagine, if you will, the lens focussing the bright star on the digital detector... Since these reflect some amount of light, the focused star's point goes back out the lens, is recollimated, reflects off the filter and forms another near focus spot (usually with some fuzz from lens aberrations) on the other side of the field center from the original focussed spot. Make sense? If you sent the full frame, your "comet" is very nearly symmentric across the field center from Vega, which is the big clue for me... I has happened before to me and why I ever shoot through filters while under the stars...

-Dean

Justin Fuller said:

Hi all,
Can anybody help me identify the object in the photo I've attached? I've crudely pointed to it. A quick scan on the Minor Planet Center and a google search of "Lyra Comet" hasn't turned anything up. Thanks for anybody that can help me

I have used mine a lot over the 14 months or so I've had it. It is certainly the easiest to use of the several tracking platforms I've got. The Astrotrac takes much longer to set up, though probably does a better job tracking. The venerable Byers Cam-Trak from the 80's is likely the best, but mine has some occasional electronic issues (takes 10m to start tracking), but will handle a 200mm lens.

The Polarie does "OK". The mount will handle up to 100mm pretty well, but not my Canon 70-200 F/2.8. I use the optional Polaris alignment scope for the ultimate accuracy. Have used both the mini-USB plug for long time-lapse sequences, but use the AA batteries too for convenience. A few of my adventures are at:

http://theketelsens.blogspot.com/2013/08/my-god-its-full-of-stars.html

A nice shot of the Catspaw w/135 lens:
http://2.bp.blogspot.com/-MPM4ef8SH9Q/VAFilXayGvI/AAAAAAAAKLA/Ih5OYlgckRY/s1600/Cat_Paw_8_frame_stack_smC.jpg

A spectacular 9-frame Milky Way mosaic:
http://theketelsens.blogspot.com/2013/09/more-star-b-que-2013.html

And the time-lapse I mentioned, using the Polarie half-speed option:
http://theketelsens.blogspot.com/2013/04/a-windy-starry-night.html

I hope you enjoy...
-Dean