The legendary 50 mm f/1.8 lens has to be one of the most popular prime lenses for many photographers. Is often nicknamed ‘plastic fantastic’ or ‘nifty-fifty’; since it combines a very wide aperture with an inexpensive construction, which makes it an excellent alternative for the typical 55mm f/5.6 kit-lens. I bought a Canon EF 50mm f/1.8 in 2010 and captured many daytime photos with it. That said, I never used it for astrophotography until recently.
The field of view with my ASI1600MM is 20×15 degrees, absolutely massive for a “telescope”. My large 800mm FL f/4 Newtonian has a field of view of only 1 degree! So what do you shoot with such a setup? I picked an obscure field on the border of the constellations Perseus and Auriga; plenty of stars to check the lens performance. Plus, the DSS red plate showed several large and very rarely imaged nebula in the field.
My Astromechanics EF adapter could control focus and I was able to get a nice V-curve in SGP’s autofocus routine after tweaking some settings. The lens has a lot of optical aberrations when used full open at f/1.8, however I found performance acceptable when stopped down to f/4. Humidity was 100% during the night. Luckily, the lens stayed clear with just a simple dew strap and I was able to collect a little over 7 hours of hydrogen-alpha data.
This was also the first time I tried the Normalize Scale Gradient script in PixInsight to stack the subs. The first sub was taken at an object altitude of 32 degrees and shows a strong light pollution gradient. I used the best sub-frame (object at 88 degrees) as reference for the script and it worked very well to reduce the impact of the light pollution gradient in the final stack.
The image below was fully calibrated and only treated with a 2-degree ABE before stretching (click for full resolution).
There are a whopping 12 Sharpless objects in this single image! I’ve made a starless inverted version to show where they are located, along with a short description of each object:
Sh2-205 – Large, faint diffuse
Sh2-206 (NGC 1491) – also known as Fossil Footprint Nebula
Sh2-207 (PK 151+02.1)
Sh2-208
Sh2-209
Sh2-210
Sh2-211 – very small
Sh2-212 – open cluster NGC 1624 lies embedded in the emission nebula
Sh2-216 (PK 158+00.1) – one of the largest known planetary nebula, 2 degrees apparent diameter
Sh2-217 – molecular cloud
Sh2-219 – small HII region
Sh2-221 (SNR 160.4+02.8) – very large supernova remnant
BFS44 – does not have a Sharpless number but appears to be a separate object and and is almost never described
The Canon EF 50mm f/1.8 II is very sharp in the center at f/4, at least with the H-alpha filter. I have not yet tested the broadband performance. 2X Drizzled crops show nice round stars and a good amount of small details in the nebulae.
It is possible to see several stars of the open cluster NGC 1624 and some dark lines inside Sh2-212 after careful stretching and sharpening of the data. Note that these details are blown out in the full field of view, which was stretched much harder to show all the faint nebulosity in other areas.
Here’s another version at 50% resolution which was processed with Starnet and noise reduction to enhance the brightness of the large nebula. It also improves visibility of the large dark dust clouds in the top right.
Date: 10 November 2021
Telescope: Canon EF 50mm f/1.8 II @f/4
Location: Herent, Belgium (Bortle 7)
Camera: ZWO ASI1600MM-C
Ha 3nm: 44 x 600s
Total time: 7.3h
For reference: my friend Axel captured some H-alpha data on Sh2-205 and Sh2-206 with his 200mm lens setup last winter. This is 100 minutes of data from Paris, France. The nebulosity is clearly very faint! There’s some great detail in the bright filaments of Sh2-206, click for higher resolution.
Astro Virus 