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Pejadee 6 4 Spain
19 Jul 2017 5:16PM
Anyone recommend a teleconverter for use with a Tamron SP 70-300mm F/4-5,6 VC Di USD lens and a Canon 70D.
themak 7 1.0k Scotland
19 Jul 2017 5:52PM
I think the standard advice with slower lenses is don't, because AF will suffer or be lost, and if you must don't go over 1.4x. Kenko make pretty good ones at reasonable cost.
dark_lord Plus
17 2.8k 778 England
19 Jul 2017 9:50PM
Kenko have a good reputation.
You will lose optical quality, and it's up to you how much you're prepared to sacrifice as zooms suffer the most.
Even with a 1.4x you'll only get AF through part of the range as the effective aperture at the long end wil be f/8 when it'll be manual focus only. o AF at all with a 2x and the effective aperture will be f/11 at the long end so be prepared for using high ISOs even in good light.

If you want longer focal lenghts then consider a prime lens and there are good value used lenses to consider which will ultimately perform better.
A Canon EF 400 mm f/5.6 would be very handy on your 70D and worth saving for.
Philh04 Plus
15 2.3k United Kingdom
20 Jul 2017 9:16AM
As has been said, not a good idea, there are really less than a hand full of zooms that will work well with and extender (Canon speak for teleconverter). Most zooms are a compromise in design and as well as extending the focal length the extender will amplify any faults in the lens, you may well be better of cropping in to the image or trying to get closer.

Your manual focus skills will need to be good as you will be MF only with a relatively dim viewfinder (the 70D will stop AF when the aperture is smaller than f5.6).

As dark lord states you will also need to be prepared to use some high ISO's as you will need to stop down 1 to 2 stops also.
Pejadee 6 4 Spain
20 Jul 2017 2:07PM
Thank you for your comments gratefully appreciated I may just save up for a super lens it is a bit of a mine field so much tech now I remember back in the 60s when I had a Polaroid camera..........LOL
20 Jul 2017 3:41PM
Pejadee, your 70D has an APS-C sensor, which means that lenses with a stated focal length eg. 70-300mm act like they are about 1.5X "longer" than on a full-frame camera sensor, ie. 105-450mm. This is also known as the crop factor as your sensor only "sees" the cropped portion of the lens image image. This is good news for telephoto users, as it uses the best and least distorted portion of the image. If you are not getting enough reach from your current combination, you would be well advised to consider your overall needs, now and into the future. If your need is driven by a passion for the kind of photography that demands a longer lens, such as in bird and wildlife photography or action sports photography, you may "need" a longer telephoto lens. Quality lenses like the Canon EF 100-400 (Series 1) is an L series pro-quality lens that can be had second hand for often half that of the newest Series 2 model. (I paid AUST $1000 for mine and the current new model is over $2400). It has very effective multi-mode Image Stabilisation which can save a couple of valuable stops, sliding zoom collar (not twist type) AND it behaves more like 150-600mm on an APS-C camera like yours! Because it is a full-frame lens, it would remain a strong investment if you decided to move up to a full-frame body like the 5D or 6D series later. My 5D MkIII with this lens produces great results. Put it on a 50 Megapixel 5Ds and you can afford to lose heaps of the image. Don't forget to consider the benefits of a solid tripod and/or monopod and don't be afraid to up the ISO (experiment with it). I remember confronting this issue with my Tamron 18-270 on my Sony 77. I tried various teleconvertors but there is a limit to what can be squezed reliably out of any budget lens. Hope this helps.
Pejadee 6 4 Spain
20 Jul 2017 4:20PM
Thank you for that in depth information much appreciatedSmile

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