Tonight I tried my hand at photographing a few Deep Sky Objects. The Hartman mask was extremely useful for focusing, but after tonight it’s clear that I’m going to need to control the D50 by tethering it to the laptop to get best results. Manipulating the zoom controls for the LCD is awkward at best. I may need to spend some time just practicing focusing on a few different stars.

Saturn was actually the first target before the DSOs. I captured a couple of images at ISO 800 and 4 sec exposure that included the moons Titan, Tethys, Dione, and Iapetus (Rhea was transiting and lost in Saturn’s glare). I reduced the exposure time several steps, but it was hard to see much detail in the LCD (another argument for tethered control), so I moved on.

Next I tried M13, the globular cluster in Hercules. This actually turned out to be the best subject of the night. One of the photos had some jitter from the wind shaking the telescope (did I mention it was occasionally quite breezy?). Most were fairly good, however, with nearly round stars — limited by the sharpness of the focus, most likely. Click the image to see a very large full-sized photograph. If you look closely you can see stars of several different colors in the cluster. M13: FL 2032mm, ISO 800, 30sec exposure, f/10.

M13

Next came M57, the Ring Nebula in Lyra. I captured several images, but they all showed noticeable wind jitter. I’m certain this is telescope vibration and not tracking error because the motion vector varies from one photograph to the next. I merged the four best frames in Registax, stretched to compensate for the motion vector, applied a gamma correction to increase the brightness, then reduced the image size to improve the apparent sharpness of the focus. M57: FL 2032mm, ISO 800, 30 sec exposure, f/10.

M57 - The Ring Nebula

The next target I tried was M27, the Dumbbell nebula. However, even with a 30 sec exposure at ISO 800 there was almost no trace of any nebulosity in the photo, so I moved on.

I decided to re-balance the telescope forward to compensate for the extra weight of the camera on the back. This, of course completed wrecked the scopes alignment so I had to restart. After alignment I focused the camera on Mizar (ζ UMa). It’s a nice blue double, but it’s included here for more than aesthetic reasons. According to SNP, the separation between Mizar A and B is 14 arc-seconds. In the unprocessed photo, the distance between the centers of the stars is approximately 19.3 pixels (along a diagonal). This puts the resolution for the camera at about 0.725 arc-seconds per pixel. By comparing similar measurements of other doubles I should be able to calculate the actual resolution more accurately. Mizar: FL 2032mm, ISO 800, 1/2 sec exposure, f/10.

Mizar A and B

After rebalancing I Attempted several images of the Whirlpool galaxy M51. The cores of M51 and its companion galaxy both appeared tiny and featureless over several photographic attempts.

Location: at home in Tomball, TX
Cloud cover: 0%
Transparency: above average (4/5)
Seeing: est. avg (3/5)
Darkness: no moon, city glow
Wind: light, less than 5 mph
Temperature: 65º+
Humidity: 45%-60%
Dew Point: 45º-55º
Time: 9:00 pm – 10:15 pm CDT
OTA: 8″ SC

Started by observing M13. Some faint individual stars appeared in averted vision. Seemed larger apparent diameter than other GCs I recall.

Next stopped at Saturn. Rhea and Titan were easily visible. Two stars (mag 10 and mag 12-13) also in the field that I mistook for Iapetus and Dione (respectively).

I wanted to spend some time observing an airy disk to estimate seeing conditions. I started with Arcturus. Very bright center, yellow-orange color. Ring pattern was usually discernible. Focusing was somewhat challenging due to variations in distortion. Radial streaks or spikes also visible. Needed 7.9mm ep to observe diffraction rings.

Also noticed there was a diffraction line across the entire FOV when using the 45º erecting prism diagonal. Line appeared with different EPs, did not appear with 90º reverse-image prism diagonal.

Finally tried observing airy disk for Spica. Blue color was striking contrast to Arcturus’ yellow-orange. Observed similar variations and distortions of airy disk as observed with Arcturus. Also noticed that the tips of the radial spikes in one direction had an orange tint. I moved the star across the FOV to see if the effect was an off-axis abberation, but the orange tips retained their orientation independent of Spica’s position in the field. Spica was about 45º altitude, so it didn’t seem like it would be an atmospheric effect. My other guess was that Spica might be a double star and that the secondary might be spectral type G or K. A quick google search shows Spica is indeed a binary double, but I haven’t yet found any info on the separation or the spectral class of the companion.

I’d say the seeing was about 4/10 on the Pickering scale, often varying between 3 and 5.