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Trifid Nebula, m20

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Posts Made By: Dave Erickson

February 28, 2016 06:12 PM Forum: Home Observatories

Areal shot of my rig

Posted By Dave Erickson

Here is an areal shot of my observatory taken this weekend 20160226. I was on site replacing a slit drive in the big dome, the on 6' dome in the foreground. The Technical Innovations new design is a major improvement over the operational for years 10 years ++ prior design...

June 15, 2016 10:17 AM Forum: CCD Imaging and Processing/Deep Sky

Gamma Cygni IC1318 area Color

Posted By Dave Erickson

Here is an image processed from narrow band data collected between May 29 and June 8 2016. Field is roughly 4X6 degrees.

July 21, 2016 09:04 AM Forum: CCD Imaging and Processing/Deep Sky

Sh2-171 and NGC7822

Posted By Dave Erickson

July was a good month for imaging during the dark of the moon. I got 18 nights and took close to 400 subframes. One of the imaging projects was Sh2-171.

Sh2-171 and NGC 7822 is a young star forming region in the constellation of Cepheus. The nebula is said to be some 900 pc distant. Some of the younger components of the system are thought to be no more than a few million years old.

The color image combines (4) Narrow band filters with
(13) 1200 second exposures for each Cyan ( OIII ), Green ( HAlpha ), and Red ( NII + SII ).

a higher resolution image is available at:

July 22, 2016 02:22 PM Forum: CCD Imaging and Processing/Deep Sky

Deneb and Friends color

Posted By Dave Erickson

Roughly 4X6 degrees centered on Deneb. The image includes the Pelican Nebula at the lower right. North is to the left. This image was aquired over several nights July 5-12, 2016.

TO me the pelican on its side with the nebula above looks like one of the travertine hot springs from Mammoth Hot springs in Yellow Stone National Park.
A higher resolution image can be found at:

July 24, 2016 03:50 PM Forum: CCD Imaging and Processing/Deep Sky

Cyguns Mosaic (4) Panes color

Posted By Dave Erickson

Most of last month was spent collecting the data for this mosaic. A total of (60) subframes at 20 minutes each or 20 hours of integration. using a 12" focal length F/4 astrograph. SHO+ StrY filters were used.

The mosaic covers roughly 6X10 degrees. The image includes SNR G82.2+5.3, Pelican Nebula, Sadr nebula area, NGC6888 and the Soap Bubble to name a few.

North is to the left...

Larger image at:

August 17, 2016 03:38 PM Forum: CCD Imaging and Processing/Deep Sky

Milky Way -21 deg dec COLOR

Posted By Dave Erickson

Here is a swath of the milky way at one of my favorite declination -23 degrees.
Taken with a 55mm F/4 Pentax lens at F/4, a good old lens although a bit slow. This 5 panel mosaic is taken from 3-camera astrograph data from a couple of years back. Finally decided to assemble some mosaics.

Higher resolution can be viewed at...

September 12, 2016 02:45 PM Forum: CCD Imaging and Processing/Deep Sky

Soul nebula, Heart nebula, Double Cluster, G132.7+

Posted By Dave Erickson

4)Panel Mosaic. This image was processed to highlight the background hydrogen cloud that is rarely imaged but present everywhere in the mosaic including the area surrounding the double cluster.

The more than 90 hours of integration are from 2015 and 2016.

higher resolution at:

September 23, 2016 09:53 AM Forum: CCD Imaging and Processing/Deep Sky

California Nebula NGC1499

Posted By Dave Erickson

California Nebula NGC1499 I added some data recently and reprocessed this image of the California Nebula.

November 7, 2010 05:12 PM Forum: Telescope Making

Figuring Dall/Kirkham primary.

Posted By Dave Erickson

Hi Joe,
Using the data from your Astromart forum posting I laid the design out in Zemax, and the system performance is good as expected. Although this is a reflective system I weighted the spot diagram below for the dark adapted (scoptopic) eye to get the Ary disk about the right size. There are geometric spot traces for on axis, 0.25” off axis and 0.5” off axis. This is the radial distance from the field center. As expected coma is the dominant aberration. Performance is good on axis and this will make a very good imaging instrument for planets, double stars, etc. as it is nearly diffraction limited over a 0.5” diameter full field. I get better performance with the primary secondary spacing of 45.900” and the modeling represents that very minor change…

For figuring this mirror, as you know it will be less correction than a parabola by a factor equal to the conic constant (K). For a parabola each knife edge position is calculated, K=-1 or 1.0*( r2 / R) where r is the zonal radius from the center of the mirror and R is the radius of curvature of the mirror. If moving both the knife edge and source use K*(r2/2R). For your scopes elliptical primary the conic constant K is -0.7578 and you’ll need to calculate the zones as 0.7578*(r2/R).

Conic Constant -0.7578
Radius of Curvature 116
Zonal increment 0.5
Parabola r^2/R
0 0
0.5 0.00163319
1 0.006532759
1.5 0.014698707
2 0.026131034
2.5 0.040829741
3 0.058794828
3.5 0.080026293
4 0.104524138
4.5 0.132288362
5 0.163318966
5.5 0.197615948
6 0.23517931
6.5 0.276009052

I looked at using the 2 foci of the ellipse as a null test but as expected the long focus (conjugate) of the ellipse is 895” almost 75 feet away with the short focus of the ellipse being 62” or 5 feet away. Thus if you placed a slit or point source 895” away and a knife edge 62” away you would cut the light uniformly across the aperture, i.e. it will null.

Well the images didn't make the posting and I couldn't attache a pdf so if you are interested send me an email to the address below and I'll forward the pdf to you...
Hope this helps…

Dave Erickson

February 5, 2012 08:22 AM Forum: CCD Imaging and Processing/Deep Sky

2011 observations

Posted By Dave Erickson

Hi Charles,
Great movie, nice website, thanks for sharing...
Dave Erickson