The most popular budget Sigma tele lenses are the Sigma 50mm – 500mm f4 – f6.3 and the Sigma 150mm – 600mm f5 – f6.3, and whilst they are classed as budget they are still quite expensive compared to other types of lenses. Whilst expensive these lenses are within the budget of most photographers, and when you consider the top end tele lenses cost several times more (and you will have to part with several thousand bucks) it is easy to see why these lenses are popular among photographers who want/need a tele lens.
The reach of these lenses is pretty impressive but if you need a little extra reach you can add a tele-converter to get even closer. There are a few different types of tele-converter available however compatibility issues can arise, especially when using third party models. Because of the compatibility issues I would always recommend using a Sigma tele-converter for Sigma lenses, even if it is a little more expensive than other third party converters.
Some third party converter manufacturers, such as Kenko, claim their converters will work with certain lens/camera combinations, and when it comes to the crunch the results are inconsistent. I would never risk buying a Kenko tele-converter to use with my Sigma lenses and I would never recommend any one else buys one for their Sigma lens either. The risk of inconsistent results, and the potential waste of money simply isn’t worth it.
There are different models of Sigma tele-converter available and each is available in 1.4x and 2x versions. When using a 1.4x tele-convert the lens becomes a stop slower and when using a 2x tele-converter the lens becomes 2 stops slower.
The reduction in light when you use a tele-converter will also affect the camera’s autofocus and, unless you are using the 1.4x converter on a top end camera, you will lose autofocus and have to focus manually. Having to focus manually will affect you but whether it is a deal breaker or not will depend on a number of factors, such as how comfortable you are at focusing manually, whether you need autofocus or not and the subjects you are shooting to name just a few.
The precise tele-converter model you need depends on what lens you intend to use it with.
Keen photographer addicted to cameras, lenses and everything photography related. Feel free to follow me in my photography ramblings, and if you have any thoughts, comments, queries or anything else to add I would love to hear from you.