Long telephoto lenses can be some of the most expensive out there, and when you need multiple focal lengths, the cost can quickly become prohibitive. Teleconverters offer a way to get more reach from lenses you already own, but they also come with drawbacks you should be aware of. This excellent, in-depth video discusses teleconverters, their pros and cons, and when they are appropriate to use.
Coming to you from Jan Wegener, this great video discusses the use of teleconverters. Teleconverters almost always come in two options: 1.4x and 2x, which denote the factor by which they increase the focal length of whatever lens you attach them to. This can be a quite affordable way to get significantly more reach out of your lenses, but it is important to be aware of the drawbacks as well. First, a 1.4x teleconverter decreases your maximum aperture by one stop, while a 2x teleconverter decreases it by two stops. Second, you can generally expect to lose some autofocus performance and image quality, particularly when using a 2x teleconverter. And with the high resolutions of many modern sensors, you may decide that simply cropping in post is the better option. Check out the video above for the full rundown from Wegener.
It depends on the lens that you are using.
Teleconverters work extremely well with most of the big, fast primes, such as 500mm f4, 600mm f4, and 800mm f5.6. You know, the lenses that cost over $10,000.
When teleconverters usually suck is when people try to use them with their cheap little 150-600mm or 100-400mm zooms. If you want truly professional results and world-class image quality, don't even bother putting a teleconverter on a cheap little zoom telephoto. If you need more reach than what your little 100-400mm or 150-600mm zoom gives you, then get a huge fast supertelephoto prime and then use a teleconverter on that. Unless you're okay with sub-par image quality ..... then you can just do whatever you want.
That might depend on what part of the image matters most to you. I recently gained an understanding of MTF charts. A lot of times, the image quality of these "cheap" zooms really falls off towards the edges pretty significantly unlike that of superteles which stays pretty high throughout. If your subjects will be at the center most of the time, you might be ok with the cheaper zooms. One thing I don't like about cheaper zooms is the variable max f-stops. Once you add a converter, you're left with max apertures of f/11 or smaller. So many considerations. At the end of the day, the long teles are probably best. But, OMG, $12K-$13K!!!
TCs don't increase the focal length of the lens. They magnify part of the image, meaning they also magnify any weaknesses.
Cropping costs you quality as well.
On the upside, they don't change the minimum focusing distance.
Actually, they DO increase the focal length of the lens. It is an actual increase in FL that you get when you add a TC to the lens.
It really depends on the lens you add the tele converter to. My personal experience matches the guidance from this video. My Canon 100-400 II does extremely well with the 1.4X extender. So much so that for most of the past 2 years it was attached permanently to this lens. This setup was replaced recently with an RF 100-500. Is my RF at 500 a lot better than my 100-400+1.4X? Actually no. Both are very good at these limits. But again the use of extenders works for: small things that are not extremely far and in good light. If your subject is too far way…it will remain too far away.
Extenders do work extremely well with large primes. The problem there is…dealing with the large prime.