Hello, firstly i hope my post is in the correct section. My question is i am using a canon 750d with a Tamron 70-300mm vc lens , can i use a teleconvertor with this camera and lens, if so which would be the best TC to purchase. Many thanks in advance, Chris.
Teleconvertors
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rob-nikon
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I don't use canon but can give you an idea about teleconverters as they work the same on all brands. They were designed for fast primes like f2.8 and f4 lenses. A 1.4x teleconverter will lose one stop of light (ie f2.8 to f4, f4 to f5.6, f5.6 to f8) but increases focal length by 0.4 (ie 300mm becomes 420mm), 2x teleconverter loses two stops of light (ie f2.8 to f5.6, f4 to f8) but doubles the focal length (ie 300mm becomes 600mm). Generally teleconverters degrade the image quality, the 1.4x teleconverter degrades the image quality less than the 2x teleconverter but is very lens dependant. The same can be said for auto focus speed, the 1.4x teleconverter slows the auto focus speed less than the 2x teleconverter, but again is very lens dependant. Generally the 1.4x teleconverter will affect the lens performance less than the 2x teleconverter but the compromise is a reduced focal length increase compared to a 2x teleconverter. The lens you are using also plays a part too, generally the faster the lye affect the lens performance. Teleconverters will affect a f2.8 lens less than a f4 lens, a f4 lens will be affected less than a f5.6 lens. There is also the possibility a teleconverter may not fit on the lens too. Some rear elements protrude too far back and would cause the rear element to come into contact with the teleconverter glass element. Regarding brands the general rule of thumb is canon lens canon teleconverter, sigma lens sigma teleconverter etc. There is the kenko teleconverter that some rate highly, it may be worth looking into over a canon of nikon one.
As you are using a tamron lens it's most likely a kenko teleconverter *may* fit it. Whether it's worth it is another question. I'm guessing your lens is already at f5.6 so you would be at f8 if a 1.4 teleconverter did fit. Auto focus could potentially not work as it may be beyond the cameras ability (most cameras are f5.6 max apart from some of the modern higher end cameras that may work up to f8, that is the case with nikon but I'm not sure with canon). Image quality may also take a hit too, potentially rendering images unusable. Sorry if this all sounds negative, unfortunately teleconverters do sound fantastic but there are some potential pitfalls you need to be aware of before going down this route and potentially make an expensive mistake.
As you are using a tamron lens it's most likely a kenko teleconverter *may* fit it. Whether it's worth it is another question. I'm guessing your lens is already at f5.6 so you would be at f8 if a 1.4 teleconverter did fit. Auto focus could potentially not work as it may be beyond the cameras ability (most cameras are f5.6 max apart from some of the modern higher end cameras that may work up to f8, that is the case with nikon but I'm not sure with canon). Image quality may also take a hit too, potentially rendering images unusable. Sorry if this all sounds negative, unfortunately teleconverters do sound fantastic but there are some potential pitfalls you need to be aware of before going down this route and potentially make an expensive mistake.
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Grumps1974
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Sound advice from Rob. I agree with him in all respects. Because you use a Tamron lens Canon teleconverters will not be compatible neither will Sigma. To my knowledge the only make you could use is a Kenko.
I had a Kenko 1.4 and used it with a Tamron 70-300 on a 5D mk3. The comments about the autofocus are correct. I suspect the combination of Tamron and Kenko teleconverter would mean you could only use manual focus on your body. I found the results a little mixed with the Kenko. Some times they were usable and sometimes they were not. I found the most acceptable results came if I did not use the combination at maximum zoom. Keeping to about 250 on the Tamron was the max. Using the 1.4 conversion this gave an actual length of 350mm. Even here the results were often not quite as good as using the Tamron lens on its own and zooming in in post production.
In the end I sold the teleconverter as I found I was not using it.
Still the Kenko's do come up for sale from time to time for £50-60 so you could buy one and see for yourself. If you don't like it you can always sell it.
I had a Kenko 1.4 and used it with a Tamron 70-300 on a 5D mk3. The comments about the autofocus are correct. I suspect the combination of Tamron and Kenko teleconverter would mean you could only use manual focus on your body. I found the results a little mixed with the Kenko. Some times they were usable and sometimes they were not. I found the most acceptable results came if I did not use the combination at maximum zoom. Keeping to about 250 on the Tamron was the max. Using the 1.4 conversion this gave an actual length of 350mm. Even here the results were often not quite as good as using the Tamron lens on its own and zooming in in post production.
In the end I sold the teleconverter as I found I was not using it.
Still the Kenko's do come up for sale from time to time for £50-60 so you could buy one and see for yourself. If you don't like it you can always sell it.
StewartR
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Rob has it right despite being a Nikon user, and that's because the fundamental issues surrounding teleconverters are driven by physics, not branding.
Your lens will have a maximum aperture of f/5.6 at the 300mm end, so a 1.4x teleconverter (if it would fit) would make it 420mm f/8. Your camera would not autofocus. This is something which Canon cameras enforce in the firmware. A few high-end cameras (1D series, 5D III, 7D II) would, but yours wouldn't. A 2x teleconverter would make your lens 600mm f/11 and no camera would autofocus with it.
You also need to check very carefully whether any given teleconverter will actually fit. Canon design theirs with protruding front elements, so the lens has to have a recessed rear element in order to fit. That way they can restrict usage to lenses which they consider will not be too seriously degraded by the teleconverter. Their equivalent to your Tamron 70-300mm is *not* compatible with teleconverters. This strongly suggests that a Canon teleconverter (or extender in Canon speak) will not physically fit on your lens. It also suggests that even if a third party teleconverter like a Kenko does fit, the image degradation is likely to be severe.
Your lens will have a maximum aperture of f/5.6 at the 300mm end, so a 1.4x teleconverter (if it would fit) would make it 420mm f/8. Your camera would not autofocus. This is something which Canon cameras enforce in the firmware. A few high-end cameras (1D series, 5D III, 7D II) would, but yours wouldn't. A 2x teleconverter would make your lens 600mm f/11 and no camera would autofocus with it.
You also need to check very carefully whether any given teleconverter will actually fit. Canon design theirs with protruding front elements, so the lens has to have a recessed rear element in order to fit. That way they can restrict usage to lenses which they consider will not be too seriously degraded by the teleconverter. Their equivalent to your Tamron 70-300mm is *not* compatible with teleconverters. This strongly suggests that a Canon teleconverter (or extender in Canon speak) will not physically fit on your lens. It also suggests that even if a third party teleconverter like a Kenko does fit, the image degradation is likely to be severe.
mikew
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Know nothing about Canon as ime a Nikon user,i have the Sigma 150-600 although i could use a converter i use a Nikon 1 series for more reach instead,could this be a option within the Canon range,smaller sensor but no light or IQ loss.