Using a Sigma Art 40mm F1.4 for astrophotography
Tired of doing mosaïcs for wide-field astrophotography? Well, a 40mm photo lens might do the job! Big question is: How good is the lens and is it good enough for astrophotography? Obviously, I cannot pass judgment on lenses I have not tested but I can tell you of my experience with a Sigma Art 40mm F1.4 DG HSM. I bought this lens second hand but in mint condition with the idea to use it for really wide field astrophotograhy. Indeed, my Newtonian has 1560mm Focal lengyh, my Askar FRA300 300mm so I needed something really short but bright if at all possible. I had heard good things about it, but there is a large gap between using a lens for day-time photography and using it for imaging the sky… While most people will tend to use a DSLR behind the lense, I really wanted to use my faithful ASI6200MC for better sensitivity and bandwidth (especially to be able to have Hydrogen Alpha band).
The camera is mounted through a Canon EF mount to a male M54 thread adaptor. Backfocus from lens to sensor with this setup is around 42mm and seems to work well enough for me. I could not find any Electronic Focuser kit (ZWO EAF) for this lens so focus has to be done manually. To focus, just monitor stars HFR while adjusting the focus crown by tiny amounts. Once you have optimum focus, draw a line with a Typex corrector pen for next time… Lens shutter is adjusted electronically, so the only way to adjust it is to connect it to a camera, adjust it and disconnect the lens from the camera. Ok, all of this is very nice, but what result can you expect to achieve with this lens? So here we are with Orion (my favorite contellation):
This picture https://c14edgehd.com/wp-content/uploads/2026/01/Orion-scaled.jpg was actually taken with the lens shuttered at F2.0. It is the result of about 5Hours cumulated exposures of 240 Seconds. My basic aim was to capture Barnard’s loop so I deem this shot a success! Obviously this is the final processed image so you might say I am cheating a bit! You’re probably dying to find out what the stars look like on the raw image, so there it is:
There is quite a bit of sagittal aberration but nothing a pixinsight and a BlurXterminator can’t correct. So, all in all, this lens really does the job!