IQ with extenders/tele converters

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Tricky69

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how good are they ?

I know they loose about 2 F stops, but how good is the glass / alignment in them

for example

if I had a 50/1.2 and a 2x tele converter it would work out at approx 100/2.5

or a 100/1.8 would be a 200/3.5

but how would the IQ be affected ?

is it worth considering ?
 
I think it depends on the quality of the lens and the quiality of the teleconverter.

I think from memory the trick is to keep the sum under f8

With that f8 in mind - the handy maths for working out if you are still going to be able to autofocus.......

A 2x teleconverter can be used on lenses with aperture at least f2.8 (becoming f.5.6)
A 1.4X teleconverter (and usually a 1.7X) can be used on a lens with an aperture of at least f4, (becoming f5.6 or f6.8)
lenses with maximum aperture of f5.6 might not autofocus with teleconverters much more than 1.4X

That said - a lot depends on the light.

Somebody else will probably know more.

I have a 2X and it works fine on a 200mm 2.8 but on my cheap 300mm it's not that good and requires manual focus.


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100/2.8 would go to 200/5.6 (2 stops)

Not typically very effective on wider lenses and 2x tend to have quite a big impact on quality on pretty much any lens.
 
Tricky69 said:
how good are they ?

I know they loose about 2 F stops, but how good is the glass / alignment in them

for example

if I had a 50/1.2 and a 2x tele converter it would work out at approx 100/2.5

or a 100/2.8 would be a 200/3.5

but how would the IQ be affected ?

is it worth considering ?
Click to expand...

Also depends on the lens. Canon TC's only fit to the L series lenses.

Canon UK
Extender is Canon's name for a teleconverter. These high-performance accessories multiply the effective focal length of an attached lens by 1.4x or 2x. For example, a 200mm lens with Extender 1.4x has an effective focal length of 280mm: with the Extender 2x, this increases to 400mm. Extenders are only compatible with selected EF lenses, including the EF 70-200mm f/2.8L USM, EF 70-200mm f/2.8L IS USM, EF 70-200mm f/4L, EF 100-400mm f/4.5-5.6L USM, EF 400mm f/4 DO IS USM and fixed length L-series lenses of 135mm or higher.
Click to expand...

So they won't work with either of your lenses, but the 3rd party manufacturer TC's might?

The TC's are really designed for the large fast L series primes. Peformance as mentioned, autofocus speeds significantly reduced, 1.4x TC, no real loss of IQs, but 2x TC does effect IQs. Also, on your 450D, you lose autofocus above f5.6 lens TC combo. So a 300mm f4 + 1.4x TC works, 300mm f4 with 2x TC won't autofocus, will only manual focus with Canon TC's.

You can get 3rd party TC's that don't tell the camera they're fitted, but these can cause the lens to hunt which can damage the lens.
 
pete.rush said:
Also depends on the lens. Canon TC's only fit to the L series lenses.

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Click to expand...

wow !!! how did I miss that ! thanks .... not a very well advertised fact !
 
pete.rush said:
Also depends on the lens. Canon TC's only fit to the L series lenses.
Click to expand...

Tricky69 said:
wow !!! how did I miss that ! thanks .... not a very well advertised fact !
Click to expand...

Mmm. You'd think Canon would do something obvious like mention it on their web site.







And funnily enough, they do.

Extenders are only compatible with selected EF lenses, including the EF 70-200mm f/2.8L USM, EF 70-200mm f/2.8L IS USM, EF 70-200mm f/4L, EF 100-400mm f/4.5-5.6L USM, EF 400mm f/4 DO IS USM and fixed length L-series lenses of 135mm or higher.
Click to expand...
 
I dont buy from the canon website *** ! ;)

I've seen and been tempted by the extenders a few times, and in a few places - but the 'L' only bit has never been in the large print !
 
The Kenko Pro 300 DG converters are of a similar quality to the Canon ones and will fit any lens, although you will get some weird results with shorter focal lengths and some zooms.

They can be picked up for about ££80-100 S/H or about £140-£160 new so they are a little cheaper than the Canon versions, and best of all they aren't white!
 
Peter10d said:
I use a Canon 2x tele con on a Canon 70-200L, and in my opinion the image quality is only slighty reduced. My bigger issue is the fact that only manual focus is available when this particular combination is used.
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Not if you are using a 1 series body!
 
Hairyduck said:
Can you not modify them as you can do with the Nikon ones?
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No. Not unless you chop half the glass off.

EdBray said:
The Kenko Pro 300 DG converters are of a similar quality to the Canon ones and will fit any lens, although you will get some weird results with shorter focal lengths and some zooms.

They can be picked up for about ££80-100 S/H or about £140-£160 new so they are a little cheaper than the Canon versions, and best of all they aren't white!
Click to expand...

Kenko won't fit EF-S lenses, which stick out too far. Not that the results would be any good as TC/Extenders only work well with high quality long lenses.
 
HoppyUK said:
Kenko won't fit EF-S lenses, which stick out too far. Not that the results would be any good as TC/Extenders only work well with high quality long lenses.
Click to expand...

I didn't know that, but then I wouldn't use a converter on a zoom (other than the telephoto Ls) and then only as a last resort.

So perhaps my statement should have read, Kenko converters will fit all manufacturers EF fit lenses.
 
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