Are Teleconverters worth investing in.

The Canon converters have a protruding front element - and cannot be fitted on many Canon lenses.
For the Canon lenses intended to work well with Canon converters with good technique you should be able to get greater image resolution than by cropping by an equivalent amount.
With converters on a DSLR you get a darker viewfinder, slower AF, and a longer equivalent focal length with more risk of camera shake - so your camera technique needs to be good to get the best out of them.
I do not know if Canon converters work with your Sigma Zoom - but a Sigma converter should.
Which macro? Not many macros from any manufacturer accept Canon converters.
An alternative is Kenko brand converters. They do not have a protruding front elements and work with a very wide range of lens. They cost less than Canor or Nikon converters - and are not far behind Canon/Nikon optical quality.
For the Canon lenses intended to work well with Canon converters with good technique you should be able to get greater image resolution than by cropping by an equivalent amount.
With converters on a DSLR you get a darker viewfinder, slower AF, and a longer equivalent focal length with more risk of camera shake - so your camera technique needs to be good to get the best out of them.
I do not know if Canon converters work with your Sigma Zoom - but a Sigma converter should.
Which macro? Not many macros from any manufacturer accept Canon converters.
An alternative is Kenko brand converters. They do not have a protruding front elements and work with a very wide range of lens. They cost less than Canor or Nikon converters - and are not far behind Canon/Nikon optical quality.

Quote:I do not know if Canon converters work with your Sigma Zoom
No they will not work, you will also need an extender that does not report aperture as AF will cease to work with a 2x and to be quite frank I would not even bother trying as the hit to image quality even with a 1.4x may be too extreme.
Canon extenders can be made to work with third party macro lenses by adding a 12mm tube between the lens and extender when a bit extra magnification is needed...

I got a 2nd hand kenko, so it could be very old. But the quality i got was about the same as i'd get from a digital zoom of the same subject. If i was to get one i'd choose it in conjunction with a particular compatible long lens or two.
Also of course they lose light so your 1/400 might become 1/100 sec all other things equal.
Also of course they lose light so your 1/400 might become 1/100 sec all other things equal.

I have a Canon 1.4X extender; Canon do not call them Teleconverters. The Canon devices are limited for use with certain lenses only. I bought mine to use with my 70-200mm f2.8 L and the performance with it fitted is hardly any different. All of the camera and lens functions operate normally using the extender. In this case the 1.4X give me 280mm but reduces the maximum aperture to f4. The 2X extender would reduce the max aperture to f5.6. The lens and camera will focus fast at f2.8 and F4 but not quite so slick at f5.6 which is why I chose the 1.4X.
Dave
Dave

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The Canon converters have a protruding front element - and cannot be fitted on many Canon lenses.
Hi Len Thanks for the advise the Kenko lens was what I was looking at getting this one seems to be more versatile and less expensive. so thanks for the advise.
Apologies for the late reply.
I cannot give hands on feedback - as I do not use Canon.
Overall I expect Canon TC's to be similar in performance to my Nikon converters.
I have not used Kenko converters for many years.
When I used them they were better than the old 1970's Nikon manual focus converters and a little behind (at a distinctly lower price) Nikon AF converters.
Kenko converters can be attached to almost all lenses but you are unlikely to get AF at f8 combinations.
ML bodies have reasonable AF ability with an f11 combination - with a much brighter viewfinder than with a DSLR.
Overall I rate ML as better than a DSLR for macro.
The Kenko instructions used to mention not to expect good quality with focal lengths shorter than 100mm.
My advice is to be realistic when using TC's.
If you do not have a long enough focal length lens I find using a converter helpful - because it puts more AF points on the subject.
For macro skittish subjects like butterflies there is the advantage of more working distance between the front of the lens and the subject.
AF points become irrelevant if you try to use a combination with too small an aperture for AF.
With extremely good technique I retain more resolution with Nikon converters than cropping by a similar amount.
Cropping by the equivalent of a 1.4 converter reduces MP on the image to 50%, and with a 2x to 25%.
It is usually distinctly easier to get good results with a 1.4x than a 2x converter.

Nikon offers a range of converters for various purposes and it's a matter of buying the right one. Is this the same for Canon?
For example the TC301 has a protruding front element which prevents its use with all but a few lenses but it performs very well with those lenses that it fits.
In general, wide angle lenses don't work well with converters. With a macro lens, the converter allows you to get much closer.
For example the TC301 has a protruding front element which prevents its use with all but a few lenses but it performs very well with those lenses that it fits.
In general, wide angle lenses don't work well with converters. With a macro lens, the converter allows you to get much closer.

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Quote:For example the TC301 has a protruding front element which prevents its use with all but a few lenses but it performs very well with those lenses that it fits.
Not much use to the O.P. though as they're using Canon, as stated.

"Worse still" - the TC301 is pre AF or even electric signal transmission - with no hope of it working either on a Sigma lens in Nikon fit - or a Nikon 200-500.
Canon, Nikon and ML converters have protruding front elements - limiting them to lenses with enough space at the back to accept a protruding front element converter.
Kenko converters do not have protruding front elements making it possible to fit them to almost all lenses, apparently with a moderate trade off in image quality.

FYI: my teleconverter experience is limited to a Nikon x1.4 Mk II which I use primarily for nature photography; although there well be an effect on image quality it is so insignificant that I can see no evidence either at 100% or in large prints.
To be fair I only use my teleconverter with prime lenses and haven't attempted to try it with a long zoom as I believe amongst other properties the teleconverter magnifies any deficiencies within the lens.
To be fair I only use my teleconverter with prime lenses and haven't attempted to try it with a long zoom as I believe amongst other properties the teleconverter magnifies any deficiencies within the lens.

Quote:FYI: my teleconverter experience is limited to a Nikon x1.4 Mk II which I use primarily for nature photography; although there well be an effect on image quality it is so insignificant that I can see no evidence either at 100% or in large prints.
To be fair I only use my teleconverter with prime lenses and haven't attempted to try it with a long zoom as I believe amongst other properties the teleconverter magnifies any deficiencies within the lens.
Using a TC also magnifies the number of pixels on the subject when you do not have a long enough focal length lens - considerable offsetting optical limitations.
If you have a pro grade zoom which accepts your TC (which is all this TC fits) - why not give it a try during the current Covid lock-down.