canon 1.7x convertor

[rene7]

Recently picked this 1.7x Jessops Canon A/F convertor in a local Charity Shop for £20, Sadly I didn't have a camera with me to try it out.
I've tried it with several Canon lenses it works fine but dies not Auto focus - any ideas why?
The lenses I tried it with were all fast lenses 135-F2, 400 - f2.8, and 85 f 1.8 so ought to have worked OK they all Auto focus with my Canon ef 2x convertor
Ta
Rene

[Simpo Two]

It might lack the required electrical connections. Does it have the same number of contacts as the Canon version?

[S1bs]

I'm guessing that the Jessops extender is quite old, possibly originally made for EOS film cameras rather than digital cameras

(Not sure who would have actually produced this, as it would have just been re-branded as Jessops for sale in the UK)

There is a known issue with very old EF 3rd party lenses.

If you google 'Old sigma lenses EF mount' you'll see a lot of discussions.

Basically, makers like Sigma / Tokina / Cosina etc have to reverse engineer the lens mount chips in order to make EF mount lenses as Canon won't share any technical information with them.

When Canon update something on the electrical connections of the mount or the AF chips, sometimes the non-Canon lenses don't have the full communication capabilities to deal with the new signals.

To be honest, if you already have a Canon 2X - that would be so much better quality than your Jessops one anyway.

The amount of light that you will gain at 1.7x compared to 2x is very small - about a third of a stop I think? So your 135mm lens would be a 270mm f4 on the high quality Canon extender compared to a 230mm f3.4 on the budget Jessops 1.7 extender. A tiny gain in aperture but with a much reduced optical performance.

Hope this helps

[rene7]

S1bs
Thanks for that, I use both the 1.4 & 2x canon convertors a lot, and always envied Nikon users with the additional choice of a 1.7x convertor, I didn't know anyone had made a 1.7x for canon so when I saw this - I took a punt, quality is fine - using manual focus and live view to assist focussing even with the Canon 'L' 800mm lens
of course A/F would be better but for what i paid I'm well pleased with it
It was worth asking on here, maybe someone else uses one and can clarify why no A/F
>
Simpo2
The connections look identical to those in the canon convertors
TA
Rene

[Simpo Two]

rene7 said:

Simpo2
The connections look identical to those in the canon convertors

So much for my cunning idea! Nor being a Canon person I can only suggest it's broken or a contact is dirty.

My lens contacts are always OK but the hotshoe needs a regular wipe with meths, maybe because it's usually exposed to the elements.

[Tony1963]

I’d go with the incompatibility with later Canon cameras. I had exactly this with an otherwise lovely Sigma lens on my 5D3. One reason I only buy Canon.

[rene7]

I've had a good search online - couldn't find another 1.7x for sale or even mentioned, nearest looking in appearance to my 1.7x Jessops is this kenko 1.4x which has a similar removal button, and identical print font, so my guess would be the Jessops 1.7x was made by Kenko [in Japan]
Optical Quality using a convertor is down to many factors - after a brief tryout with my 600 & 800mm lenses I reckon it's optics are similar to a canon 2x, but of course with less magnification and saving at least 1/3 stop, [very significant with these long lenses] so I got a bargain even for a 'manual' focus Canon A/Fconvertor
Thanks to everyone who replied - I'm really surprised no-one else has a 1.7x If you see one for sale cheap then IMO its a bargain if like me you'll use it only on long lenses.
TA
Reme

[Smollet]

Tbh until I saw this post I wasn’t aware a 1.7 option existed and assumed it was a typo.