When we think of Astrophotography visions of large refractors coupled with dedicated astro cams, cooling technology, computers, guide scopes all come to mind. Hi-tech fancy equipment is nice but not entirely necessary to capture sights such as the picture above.
In full disclosure the nebulas were shot using some equipment primarily for Astrophotography. A CLS-CCD clip filter for Canon helped draw out the Horsehead and Running Man Nebulas while the Orion Nebula would be bright enough on it’s own to capture parts of it without a filter. Agena Astro carries the Optolong version of this filter starting at $115 plus shipping. There are different versions of a CLS filter and choosing one will depend on your setup. Using my modified camera (IR cut filter removed) the optimal filter would be a CLS-CCD. The CLS-CCD will remove enough light pollution to capture nebulas but will add back some of the IR Cut that was removed by the modification while allowing more useful light to pass through. In short it will provide more contrast to the objects you are capturing. Using a straight CLS filter will block the sodium light emissions given off by street lamps, buildings and surrounding areas but will also allow the IR spectrum to fully pass through causing your photos to become more “red” in color if your IR cut filter has been removed from the sensor. Another drawback to using the CLS only version in modded cameras are focus issues. IR light emissions as noted will pass through but your sensor cannot tell the different between IR light and good light with the cut filter taken out of the picture so to speak and you will end up focusing on the IR light, which will create a halo effect around your stars instead.
The Sigma 150-600mm lens is a great lens for long distance, nature and sport photography. I quite frequently use it to capture my sons baseball games. The dedicated sport version of this lens is just as good but carries a heftier price tag. The major difference is the sport is made to withstand the elements a bit better than the contemporary. The contemporary is lighter than the sport version which makes it a better astro choice if you’re choosing one over the other. Among long range lenses this is one of the sharper models on the market when it comes to detail quality. While looking for this lens you may find the older Sigma 120-400mm in comparison at significantly lower costs. Let me be the first to tell you there is absolutely no comparison when it comes to sharpness and details between the 120-400mm and 150-600mm both of which I have owned. The older version is much softer at the long end inevitably finding yourself frustrated with the results. If you’re looking to mold your astrophotography hobby with your sport/nature photography do yourself a favor and steer clear of the 120-400mm. The 120-400 is not a terrible lens it just won’t cut it for what you’re looking to do. I was pleasantly surprised at how much detail this captured for a non-dedicated astrophotography lens. Longer subs would have yielded more contrast but alas the freezing Chicago winter got the best of me.
The only issue I found using this lens was not having a dedicated focus knob and it’s a bit heavier in weight. The focus ring is on the lens tube and any slight movement will shake your setup immensely. Focusing becomes a very tedious task as you have to make very slight adjustments, wait for the lens to stop shaking, check your focus, and make more adjustments. Even with a Bhatinov mask it took me about 30 minutes to find a focus I was comfortable with. I was still not happy with the final focus after all that. There are motorized focus rings available that would probably solve that issue but to date I have never tried or have plans to try one on this lens.
I was able to crop in the Orion Nebula fairly close. Of course the final exposure is enhanced in photoshop but without the sharpness of the lens it would not be easy to crop without introducing artifacts in to the final image. There is some minor vertical banding that was evident. I do not believe this was a byproduct of the lens, instead it was more than likely camera sensor related since I see this on my other images with different scopes. I’ll be introducing dithering in the future with my new ASIAIR setup to help reduce those types of artifacts going forward.
The overall weight of the lens can be an issue. It’s no featherweight at 4.25lbs and will require a very balanced counterweight on lighter setups and additional camera gear. I about maxed out my Sky Watcher Star Adventurer and had to add an additional counterweight to help the mount co-exist with this lens. Probably not the most ideal situation to begin with but you make do with what you have at the time. Extending the focal length also extends the lens outward and will require re-balancing each time. Ideally the focal length will be set and locked in prior to balancing on lightweight mounts.
If you are on the fence about astrophotography and own or have access to a long lens take a stab at using it for a few sessions shooting the the brighter nebula such as Orion in the winter months. You will have some star trailing and won’t produce the full spectrum of light without mods but it will give you an idea if sitting out in the cold and waiting out long cloud patches is something you’re willing to be patient with.