Tele-Converter: will it work?

[philc]

I have a Sony Alpha 550 DSLR and a Sigma APO DG 70-300mm f4-5.6 lens. I would like to buy a 1.4 X teleconverter to extend this lens. Is there one which will work in Auto modes with this combination? And would it also work with my Sigma APO 170-500mm f5-6.3 lens?

[thefonz78]

I think Sigma make teleconverter so they should work with that.

[Markulous]

I use the Kenko Pro300 DG 1.4x and find it very good (as good as the Canon Mk II 1.4x which is twice the price so I sold it!) and it'll work (don't necessarily recommend from these guys!) Kenko PRO 300 AF 1.4x Teleconverter for Minolta and Sony

Don't know the Sigma TC but it'll work Sigma 1.4X Teleconverter EX APO DG

And that's the good news! No probs with light meter working to set the aperture/speed but AF probably won't work (TCs will take the max aperture over the 'magic' F/8 limit where AF is usually switched off as the camera manufacturer reckons you're unlikely to get sufficient contrast for AF to work well)

Having said that, I don't know if Sony sets this F/8 limit and the "tape trick" will probably work to fool the camera (put a piece of sticky tape over a couple of the TC pins so camera fails to recognise the TC attached and allows AF to work - I use this on my Canon/Kenko/Sigma combo)

[MattUK]

http://www.sigmaphoto.com/sigma-lens...tability-chart

[OldBoy]

Originally Posted by philc

I have a Sony Alpha 550 DSLR and a Sigma APO DG 70-300mm f4-5.6 lens. I would like to buy a 1.4 X teleconverter to extend this lens. Is there one which will work in Auto modes with this combination? And would it also work with my Sigma APO 170-500mm f5-6.3 lens?

Sorry, but the Sigma converter won't work with that lens. As a general rule teleconverters will only work with F4 lenses or above. Kenco might work but it will be manual focus only.

[philc]

Many thanks to the 4 of you for your replies.

Thefonz78encouraged me by suggesting the Sigma TC would work but Mallik gave me a link to a Sigma compatability chart which failed to include either of my lenses; OldBoy stated straight out that the Sigma TC will not work with my lenses; and the link Markulous gave also fails to list my lenses.!

So that seems to leave me with the Kenco possibility which I shall explore more closely. Markulous, please be kind enough to explain more precisely what the "tape trick" is. Which of the TC pins? On the TC itself I presume? Do uyou use gaffer tape or something thinner?

Thanks again everyone. I thought it wasn't quite straightforward!

[Cathus]

I've got a Sigma 1.4TC which I have used with my Sigma 50-500, you lose a stop of light and autofocus, unless you have lots of light it's not really worth the trouble.

[Markulous]

Yeah, think the Sigma suffers from the same problems as the Canon, namely that the lens assembly protrudes from the TC and so can foul certain lenses. The Kenko doesn't have this disadvantage and so I use it on all my lenses (though yet to try it with the MPE 65mm!!)

The "tape trick" works very well and I use it regularly - I've even stacked 2 x 1.4x TCs and still maintained AF (and, more importantly, achieved halfway decent pics - near as good as any without any TCs)! Yes, you lose 1 stop per 1.4x TC and yes, you need pretty good light (as the AF depends on contrast differences for accuracy) and yes, you lose some IQ but when needs must...........

Here's more info on TCs and how to perform the "tape trick"
Kenko 2x Teleplus Pro 300 Teleconverter

BTW, think the latest TC is the DGX version of the Kenko Pro300 1.4x

[OldBoy]

Originally Posted by Markulous

Yeah, think the Sigma suffers from the same problems as the Canon, namely that the lens assembly protrudes from the TC and so can foul certain lenses.

On the Stigma 50-500mm F4-6.3 you have a switch to lock it 100mm before fitting the converter to stop it going below that. It works a treat with the 1.4 converter fitted but it's manual focus only even on a pro camera. As Cathus says, you do need bright sunlight to get the best out of it. It's one of the exceptions I stated above, as most lenses won't work with a converter if they are more than F4, and if they did the results may not be worth the trouble.

[Markulous]

Originally Posted by OldBoy

<snip> as most lenses won't work with a converter if they are more than F4

As stated above (twice!), they can be made to "work" (by which I assume you mean AF as shutter/aperture's fine and obviously they do magnify by 1.4x!)

Originally Posted by OldBoy

<snip> and if they did the results may not be worth the trouble.

As stated above (twice!), they are definitely worth the trouble (personally, never found they've not been worth the trouble, and worked well - even stacked!)