Teleconverters - any good?

[ianmeads]

Hi

I'm very new to the DSLR activity and have a Canon EOS 450D with a Canon 18-55mm IS and a Tamron 70-300mm, f4-5.6 DI lenses.

I was to start taking more wildlife shots but lack the lens to do it and the funds to do a great deal about it. Therefore a friend suggested getting a teleconverter which, while perhaps not being perfect, will let me get closer and learn the skills for when the big lens can be bought.

I was looking at the Kenko Teleplus MC4 DGX 2x Canon AF Teleconverter as a possible. I know that I'll lose some stops but I have a few questions that I'd be grateful for some advice on:

Will it work with my camera and lens combination?
Will I loose anything else such as auto-focus?
Are they any alternatives (around the same price) worth considering eg the Jessops 2X Converter?

Sorry if these are stupid questions but I'm confused with all the options!

Thanks in advance for any help.

Ian

[chris-p]

Hi Ian, welcome to the forums

I don't know about the Jessops one but the Kenko one will work and you won't loose autofocus (it's an AF teleconverter).

I've never actually used a t-con myself but I think that a 2x one means you'll loose 2 aperture stops so you'll need pretty good light with your 70-300 as you'll only get f/11 at 300mm. having said that, on a bright day it shouldn't be a problem at all.

If the Tamron has a stabiliser in that will help as well, if not just try to keep your shutter speed above the reciprocal of the focal length (ie, at 300mm try to keep shutter speed above 1/300th).

[ianmeads]

Thanks very much - may have to treat myself!

[OldBoy]

Using a teleconverter on that lens you will loose auto-focus. I use converters 1.4 and 2x on my F2.8 or F4 lens and still have auto-focus. On Canons anything over F5.6 and you lose auto-focus and with nikons it's F6.3 unless it's a pro camera and it's good for F8.

[chris-p]

Just as well you came along OB - I assumed that an AF Tcon meant working AF!!

[flake]

AF Tcon means that it will support Auto focus when the camera is able to.

However you have a more significant issue when trying to pair this lens with a teleconverter, and that is that it simply isn't compatible (according to the WEx site). Not all lenses are unfortunately.

The Tamron is something of a bargain basement lens and if you have some spare cash it might be better to think about a 70 - 200 f/2.8 Sigma or a 100 - 300mm f/4 second user. You will get far better results than with the Tamron.

Even if it were possible to use this lens with a TC I think trying to use it as a 140 - 600mm would be a nightmare. Long lenses are very unforgiving as the depth of field becomes very limited, and shutter speeds need to be quite fast, hand holding in all but the brightest light will be out of the question. Your widest aperture will be f/11 which is anything but fast, you might be able to use it for images of the moon, but anything which moves will be impossible.

My advice is to seriously consider changing this lens to something more suitable, another cheap way would be the Sigma 50 - 500mm which again isn't tremendously fast, but it's much better than what you are thinking of.

[OldBoy]

Originally Posted by chris-p

Just as well you came along OB - I assumed that an AF Tcon meant working AF!!

Yes, AF Tcon will auto-focus but only when the maxium F-number is F6.3 or less with it attached. So a F2.8 lens would give you a F5.6 with the teleconverter. If it's an F4 lens then it would go to F8 which means only semi-pro or pro cameras would still retain auto-focus.

[flake]

Originally Posted by OldBoy

Yes, AF Tcon will auto-focus but only when the maxium F-number is F6.3 or less with it attached. So a F2.8 lens would give you a F5.6 with the teleconverter. If it's an F4 lens then it would go to F8 which means only semi-pro or pro cameras would still retain auto-focus.

For a Canon it's a minimum of f/5.6 so far as I know it's also the same for a Nikon The Sigma 50 - 500mm f/4.5 - 6.3 retains autofocus by telling the camera body that it is an f/5.6 and fools it into retaining autofocus.

There's a thread on Flikr about this here

I'm sure we've discussed this before Oldboy when you asked how the Bigma managed to retain autofocus at f/6.3

[lifecapture]

You could buy the kenko and try taping over a combination of pins to trick the camera, though dont expect stellar performance. The degradation in quality will be awful, thats not a brilliant piece of glass you have there, go for a 1.4x converter your keeper rate will go up.