** I've been hosting my images on a WordPress blog for the past 2 years. However, WordPress has recently made it very difficult to share full resolution images, so I decided to upload everything on AstroBin. **

2020 was honestly extremely frustrating, and I almost gave up astrophotography. I had invested a lot in quality optics and high-precision collimation tools, but the images from my high resolution ONTC Newtonian setup were never ‘good’. I wasted hours and hours of precious clear sky time on testing, and could not identify the root cause.

That’s why I decided to explore the opposite end of the telescope spectrum in 2021: camera lenses. Several manufacturers produce lens adapters that fit both a lens bajonet (e.g. Canon EF mount, or Nikon F-mount) and astrocamera screwed treads (e.g. M42). However, these adapters are completely passive pieces of metal: they cannot control the electronics inside modern camera lenses. A small business in Russia called Astromechanics has developed a smart lens adapter for Canon EF lenses, that can operate the focus motor and aperture blades through an ASCOM interface. I bought the M42x0.75 model for my ZWO ASI1600mm-C camera and paired it with a Sigma 105 mm f/2.8 EX DG macro lens.



The construction of the lens adapter is very solid. Manufacturing tolerances appear to be controlled well, as both my Canon EF 50 mm f/1.8 and Sigma 105 mm f/2.8 lenses fit very snug to the adapter without noticeable play. This is important, as any lens movement (sag) will result in a tilted focal plane and out-of-focus stars, especially on fast optics.Focus position can be controlled through ASCOM, while the aperture must be set in the lens driver window. I tried to use autofocus curves in SGP, but results were not consistent. The focus motor inside my Sigma lens does not have absolute positioning, and tends to slip. Focus was often better after manually adjustment (couple steps up or down). The lens is also soft at maximum aperture (f/2.8), and sharpness improves significantly by stopping down to f/4 or f/5.6. The images below were captured with a red filter.



Sigma used low-dispersion glass in the lens design (EX-series) to reduce chromatic aberrations, but RGB filters clearly do not focus at the same positions.My plan was to shoot a huge mosaic in the Summer of 2021, but all we got was clouds and rain. It’s been over 100 years since we had this much precipitation in a Belgian Summer! So I focused on a couple less ambitious projects instead. The first was a single field of 9×7 degrees wide in the constellation Cepheus. The resulting image shows multiple nebulae, with the popular ”Elephant Trunk” nebula in the lower left, and much harder red ”Bat nebula” (Sh2-129) and extremely faint blue ”Squid nebula” (Ou4) in the top right.

Ou4 is barely visible above the noise floor, even with 7.5 hours of exposure time through a 3nm OIII filter. Processing starless data was a must. This type of low-brightness objects would really benefit from darker sites.