kenko teleconverters

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quanta

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ok, stupid question and i hope *** wont mind :D
i own a 450D and a 55-250mm IS lens. can you guys tell me whether the kenko tele extenders (all or any specific ones) work with this combo?
i am just looking to extend my range and thought this would be the cheapest option (if it works).
 
They might fit, I don't know, but you will not be able to autofocus. Teleconverters reduce the maximum aperture of the lens and once the aperture goes smaller than f5.6, the camera will turn off the autofocus.
 
Sorry, but they wont fit.
 
I thought the Kenko teleconverters worked with most lenses. The 1.4x would lose you a stop but if your lens was f4.5 then you would retain your autofocus. Sure somebody will correct me if that's wrong.
 
From the B&H website-quote-

'Teleconverters are best used with longer telephoto lenses and are not recommended for lenses wider than 50mm, e.g. 28-105mm. However, full AF operation is only possible with lenses with open aperture of f/2.8 or brighter. Please be aware that AF will work properly only if there is enough light and contrast on the subject to activate the camera's AF sensors. Manual focusing is recommended when using lenses with smaller open f-stop value than those given above.
Note: Not compatible with the Canon Digital-only EF-S lenses, 18-55 f/3.5-5.6, 17-85 f/4-5.6, 60 f/2.8 macro etc.'

The minimum lens I would use with a TC would be a 70-200mm L USM.
The 55-250mm IS is NOT compatable.
 
When adding a 1.4TC, whilst your focal length increases, your f-ratio decreases. Canon AF mechanisms on all but the top pro cameras work to F5.6. Putting a 1.4TC means that focus will only be retained one stop better or at f4. The 55-250 moves past F4 at 74mm so whilst you may be physically able to mount the 55-250 with TC on the lens, you'll lose auto focus at 74mm x 1.4 = 103.6mm. Given the lens can get to 250mm without the TC, it's probably a fruitless exercise ;)
 
arad85 said:
When adding a 1.4TC, whilst your focal length increases, your f-ratio decreases. Canon AF mechanisms on all but the top pro cameras work to F5.6. Putting a 1.4TC means that focus will only be retained one stop better or at f4. The 55-250 moves past F4 at 74mm so whilst you may be physically able to mount the 55-250 with TC on the lens, you'll lose auto focus at 74mm x 1.4 = 103.6mm. Given the lens can get to 250mm without the TC, it's probably a fruitless exercise ;)
Click to expand...

What he said!

Additionally, as EF-S lenses are designed for smaller sensors, the rear element extends past the mount, meaning a TC won't physically fit :)
 
Jazzmonkey said:
I thought the Kenko teleconverters worked with most lenses. The 1.4x would lose you a stop but if your lens was f4.5 then you would retain your autofocus. Sure somebody will correct me if that's wrong.
Click to expand...

I got a 1.4 Kenco PRO300 last week. I have it on my D300s with a 70 - 300mm Nikkor.
Minimum aperture is f.8. Auto focus works fine.
Problem may occur on a very dull, though.
 
thanks guys. very useful (and depressing :P) info. so my other cheap option is to get the longer canon lens or the bigma :thinking:
not sure whether i want to go those ways anyway..
 
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