Cassiopeia Observatory

D7000 DSLR Imaging: Flame & Horsehead Nebulae

Posted: 17 December 2012

As forecast (see my previous report), clouds and rain did arrive on Thursday, 13 December, 2012, so I wasn't able to observe the Geminid Meteor Shower at its peak. Received 0.8" rain by sunrise on Friday, with an additional 0.2" during the day on Friday, for a total of 1" from the winter storm. Some snow fell after sunrise and but very little of it stuck around. Had a little more rain on Saturday from a second storm, and an additional 0.6" early Sunday morning. Sunday afternoon I wiped off rain water from the dome and did a little maintenance on the POD door seal. A small crack had developed in the rubber seal in one corner, letting rain water drip inside the observatory at the door. Nothing major; just a nuisance that was easily fixed.

Finally, the sky cleared late Sunday afternoon, 16 December 2012, and the observatory was opened at 2218 MST, 37°F. The humidity was 73%. At 2228 MST, as I was preparing to view an object in the 8" LX200-ACF, I saw two Geminid meteors. I then viewed M42 at 77X. At 2244 MST, I began preparing the D7000 DSLR for prime focus + focal reducer + Off-Axis Guider (OAG) imaging of the Flame and Horsehead Nebula.

At 2253 MST, I did a focus test with Bahtinov Mask on the star Betelgeuse. I then did some framing test exposures at 1 minute, ISO 6400. Both nebulae easily showed in this short exposure, making framing easy. I found an excellent guide star to use with the OAG and did six guided 5 minute, ISO 6400, exposures. When I checked the images on the camera, two were discovered to have a satellite trail through the Flame Nebula. So, I did two more guided 5 minute, ISO 6400, exposures, making a total of 6 good exposures to stack (using Keith's Image Stacker) for an effective exposure length of 30 minutes.

This image is one of the unedited, guided 5 minute, ISO 6400, exposures, to show a before-stacking example:

Notice the reflection (lower right) of the star Alnitak (upper left). I edited most of the reflection out before stacking. This is the stacked image:

I completed imaging at 2355 MST. I removed the camera but left the focal reducer attached. I then began observing with the 26mm eyepiece to try for the Horsehead Nebula. The Flame Nebula was easily seen but the Horsehead remained elusive, even when bright stars were slewed out of the field-of-view. I added a O-III filter and could just barely see the Horsehead Nebula.

The observatory was closed at 0024 MST, 38°F. When I closed the dome I noticed that there was frost on the dome.

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