Sigma 150mm loses AF with Sigma 2X convertor?

[Miyagi-san]

I was going to post this in "lenses" but figured it would be better suited here. Sorry if I'm wrong! :)

I just got my Sigma 150mm2.8 and Sigma 2X convertor....

I could have sworn I read on the board here that you can use the 2 together and retain AF....but it is definitely not working when I mate the combo up to my 300D....the LCD displays max f5.6 though....

Not a big deal really, as this is a lens that will see a lot of MF anyway :D But just making absolutely sure that it indeed should not be working?

Thank you!

[racketman]

My Sigma 150 can AF with my Sigma 1.4 TC but sometimes I have to turn the camera off and on again to ge the AF working. Its a slow focusing lens at the best of times - dont use it for birds / sport!

[LordV]

Suspect that's correct- think the AF suspends operation if the effective max aperture is F5.6 or smaller and it sounds like the aperture is being reported correctly for the lens combo. With a 1.4X TC the effective aperure is wider and the AF can work. This is done to protect the AF motor as it will hunt very badly in the effective low light situation.
Brian V.

[Miyagi-san]

ahhhh, I see. That makes sense, oh well...not a big loss. Just as quick to MF on a macro lens anyway :D

Thanks! finally getting out today to test this baby out.... :D

[photobitz]

It should actually work... you may find however it won't work well in low light. Also, the 300D is not renowned for low-light focus ability. I'd say you'd see a vast improvement on a 20D/30D which have better AF assist beams. Same was true for my EOS500 and EOS50 film bodies. The EOS50 would focus where the cheaper bodies would just hunt around.

[Lester Wareham]

No it should work, my EF 200/2.8 + EF 2X II still AF's OK. It must be some Sigma compatibility issue.

[CyberDyneSystems]

It definitely SHOULD work, as f/5.6 or larger is the point from which AF should work. (including f/5.6)

However, Sigma lenses and Canon Bodies have a number of oddities in this regard, and this is just the most recent "AF with T-con" oddity I have heard of.

The T-Con Sticky thread if EF lens forum discusses some of the others, it seems that with Sigma lens + T-con + Canon body we can not actually guarantee many combos to work.

P.S. I did move this to the Lens forum, but I left a re-direct in Macro.. so people will see the thread in both forums.

[asylumxl]

nobody mentioned the seletape trick?

[Lester Wareham]

nobody mentioned the seletape trick?

Well he shouldn't need to use it, but it might work in this case. I tried it with a 300/4 + 2X and it was rubbish.

It may also be worth him checking all the connectors are clean on lens, tcon and body just in case Sigma have got it right.

[Mr. Clean]

My Sigma 70-200 2.8 + 2X TC worked on my 30D. Maybe it's a 300D compatability issue :p

[Miyagi-san]

hmmm, well thanks for the additional input. after reading it, i grabbed camera, lens and convertor and tried again.....

tried everything, different focus settings, turning camera off and on....

it definitely does not work. i will chalk this up as one of those things that may happen when with a teleconvertor. all contacts are clean and the convertor is brand new, lens focuses as it should without it...

oh well, i've heard a horror story or two about taping connectors....not worth even a small chance of risk with a lens of this type.

thanks again everyone, i wish the weather would warm up!

[photobitz]

Just curious... does it work OK with any other lenses? Perhaps you have a dud TC where not all the pins make contact or there's a broken circuit or something?

[Miyagi-san]

Just curious... does it work OK with any other lenses? Perhaps you have a dud TC where not all the pins make contact or there's a broken circuit or something?


Good suggestion, as I didn't even think to try that....however it will not physically mate up with anything else in my arsenal :p

Included in the instruction manual is a chart of lenses that displays what lenses will work with it, and if they will have AF or MF...and the 150mm I am trying to use with it is not even listed in the chart.

thought I did my research on this one....thankfully as it's a macro lens it's not a big issue. would be nice if it worked though

[photobitz]

Personally, I would still want to use the 150mm for non-macro too, although probably not with a 2x TC... Could you take it to a shop and try it out with another lens that is on that chart? If it won't AF at 2.8, there aren't many lenses left to use it with are there? (and still get AF that is)