HarryImp
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70-300 Is USM With Teleconvertor Help Please

Fri Jul 22, 2011 3:16 pm

Hi all

I have got a 70-300 IS USM f/4-5.6 but fancy a bit more reach. I thought a 1.4X TC was out of the equation because I lose AF. However I was speaking to someone to day who showed me had a 75-300 III USM with a Kennko 1.4X teleconvertor and the AF was totally unaffected??

So would i be able to use a TC or not???


Harry
 
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lgw340
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RE: 70-300 Is USM With Teleconvertor Help Please

Fri Jul 22, 2011 3:31 pm

You can use a Kenko tele converter which will be fine for reading regs etc but will not be good enough for uploads here. The Canon EF 1.4x and 2x will not fit the 70-300 IS.
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HarryImp
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RE: 70-300 Is USM With Teleconvertor Help Please

Fri Jul 22, 2011 3:34 pm

Will the AF still work???


May I ask why it wont be good enough for uploads on here??
 
othic
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RE: 70-300 Is USM With Teleconvertor Help Please

Fri Jul 22, 2011 3:38 pm

AF will NOT work

/othic
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HarryImp
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RE: 70-300 Is USM With Teleconvertor Help Please

Fri Jul 22, 2011 3:41 pm

Hmm ok... well how come this bloke with a 75-300 III USM managed too? I thought the same as you but it baffled me!!

Harry
 
legoguy
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RE: 70-300 Is USM With Teleconvertor Help Please

Fri Jul 22, 2011 7:07 pm

Depending on which Kenko 1.4x converter it is, autofocus may work. I believe the older converter will allow the camera to attempt to autofocus, but half the time may not work unless the conditions are quite bright and contrasty, i.e nice bright sunlight.

I have had two Kenko teleconverters, both 1.4x. The older version allowed autofocusing whilst from memory the newer version (PRO 300) did not. As with any teleconverter, taping up several connecting pins allows the camera to try autofocusing but the accuracy of the focusing may not be 100% and this method it not really recommended. I think I read that it can perhaps burn out the autofocus motor in the lens.

As LGW340, the Canon 1.4x and 2x extender's do not physically fit on the Canon 70-300mm IS USM, they only fit on L range lenses. Kenko teleconveter do however fit, but the results can be iffy. From the resulting images, you might get one or two good shots as the 70-300mm is a good lens, but the majority will not be the best of quality.

I hope this helps a bit,

Dave
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ckw
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RE: 70-300 Is USM With Teleconvertor Help Please

Fri Jul 22, 2011 11:51 pm

With Canon convertors, there is a pin which communicates with the lens to determine the effective aperture. On non-pro cameras, Canon has decided that accurate auto-focus cannot be acheived at apertures smaller than f5.6, hence they have built in an autofocus limiter.

3rd party manufacturers do not normally incorporate this extra pin, hence the camera will not be limited in attempting to autofocus.

The problem is that the autofocus process is not a simple on/off - it depends on light and contrast. In some situations (good light and contrast) the 300 f4-f5.6 will work fine with a convertor, in others it won't.

Its a bit like limiting the top speed of certain cars - they CAN go faster, but certain components (usually the tires) cannot guarantee the necessary level of safety beyond a certain speed. Go beyond that speed in a straight line, you're probably ok - start cornering hard and you're in trouble.

Cheers,

Colin
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vikkyvik
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RE: 70-300 Is USM With Teleconvertor Help Please

Sat Jul 23, 2011 12:06 am

Quoting ckw (Reply 6):
Canon has decided that accurate auto-focus cannot be acheived at apertures smaller than f5.6, hence they have built in an autofocus limiter.

Is that with a lens + TC?

Just curious, as I use my F3.5 18-55 lens all the time with my 1000D (no TC, obviously).
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lgw340
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RE: 70-300 Is USM With Teleconvertor Help Please

Sat Jul 23, 2011 7:43 am

The lens WILL AF with the converter.
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HarryImp
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RE: 70-300 Is USM With Teleconvertor Help Please

Sat Jul 23, 2011 8:19 am

Ok thanks


So it will work?? Or not all the time?? Which Kenko convertor will I want?

What difference will it make to the quality of the picture??? I want good pictures, but i dont think will ever be up to Airliners standard for a while yet anyway. So i am just concentrating it for my own benefit atm. Wht visual changes will i see??


Harry






Harry
 
eggohoek
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RE: 70-300 Is USM With Teleconvertor Help Please

Sat Jul 23, 2011 11:33 am

If you stick down the last 3 detectors of Kenko TC you get AF. But you get very bad picture quality if you use Canon 70-300 IS with TC. If you need extra focal length better choice to buy a lens with 400 mm focal length.

TC's made first of all to prime lenses, but you can use TC with Canon 70-200 L series (1,4x will better like 2x).
I tried 70-200 f4 L IS with Kenko 1,4x and that combo gives better quality like 70-300 IS. But the better choice if you don't use TC with zoom lens (buy a zoom with 400mm).
 
trvyyz
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RE: 70-300 Is USM With Teleconvertor Help Please

Sat Jul 23, 2011 3:13 pm

I had used this lens with a tamron 1.4x convertor in the past. it does autofocus, but hunted crazily, so annoying that you feel to opt for MF instead. The picture quality will not be that great anyways.
 
ckw
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RE: 70-300 Is USM With Teleconvertor Help Please

Sat Jul 23, 2011 11:51 pm

Quoting vikkyvik (Reply 7):
Quoting ckw (Reply 6):
Canon has decided that accurate auto-focus cannot be acheived at apertures smaller than f5.6, hence they have built in an autofocus limiter.

Is that with a lens + TC?

Just curious, as I use my F3.5 18-55 lens all the time with my 1000D (no TC, obviously).

Sorry, sometimes this gets confusing. The smalller the NUMBER the larger the APERTURE - so 3.5 is a larger aperture than 5.6, f16 is a smaller aperture than f8 - by smaller and larger I'm refering to the diameter of the iris, which determines the amount of light reaching the AF mechanism.

Canon has set aribratry limits on AF - any aperture smaller than f5.6 (f8, f11, f16 etc) will not focus on a non-pro camera. Pro cameras can still AF at f8

Quoting HarryImp (Reply 9):
So it will work?? Or not all the time?? Which Kenko convertor will I want?

What difference will it make to the quality of the picture??? I want good pictures, but i dont think will ever be up to Airliners standard for a while yet anyway. So i am just concentrating it for my own benefit atm. Wht visual changes will i see??


Yes, it will work. Sometimes. And it may be slow and hunt a lot.

In terms of quality, you will see less sharpness and contrast. I'm afraid you can't have a definitive answer to this - what is acceptable in terms in image quality is a personal thing,

Cheers,

Colin
Colin K. Work, Pixstel
 
vikkyvik
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RE: 70-300 Is USM With Teleconvertor Help Please

Sun Jul 24, 2011 9:01 pm

Quoting ckw (Reply 12):

Ah sorry that was my mistake. However my real question was whether you were referring to lens + TC specifically. Hard to imagine that Canon consumer cameras won't focus at F8. I use my camera out to F16 and beyond with AF all the time!
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McG1967
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RE: 70-300 Is USM With Teleconvertor Help Please

Sun Jul 24, 2011 9:24 pm

Quoting vikkyvik (Reply 13):
However my real question was whether you were referring to lens + TC specifically. Hard to imagine that Canon consumer cameras won't focus at F8

If you are using a Canon 400mm F5.6L, and you add a 1.4xTC to it, then the largest aperture with this combo of lens & TC becomes F8. The only Canons that will Autofocus with this combo at an F8 aperture is a pro camera.

If you are using a Canon 300mm F4L IS and you add a 1.4xTC to it, then the largest aperture with this combo of lens & TC becomes F5.6. The Canon consumer range should autofucus with this combo at an aperture of F5.6.
 
ckw
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RE: 70-300 Is USM With Teleconvertor Help Please

Sun Jul 24, 2011 11:28 pm

Quoting vikkyvik (Reply 13):
Ah sorry that was my mistake. However my real question was whether you were referring to lens + TC specifically. Hard to imagine that Canon consumer cameras won't focus at F8. I use my camera out to F16 and beyond with AF all the time!

Bit of confusion here - what we are talking about is the maximum aperture of the lens. Regardless of which aperture you set, autofocus is performed with the lens wide open - it only shuts down to the your selected aperture at the moment of exposure.

Canon (and indeed ALL AF cameras) require a certain amount of light (or strictly speaking contrast) to accurately focus. The key figure is the f stop of the lens wide open. If you add a 2x convertor, this figure is reduced by 2 stops (an f4 lens becomes an f8) , by 1 stop for a 1.4 convertor.

Cheers,

Colin
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vikkyvik
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RE: 70-300 Is USM With Teleconvertor Help Please

Mon Jul 25, 2011 12:46 am

Quoting McG1967 (Reply 14):
Quoting ckw (Reply 15):

Ohhh, OK, I am vastly less confused now  

I did know about cameras focusing at the widest possible aperture, but it didn't register that that would change with a TC (probably since I've never used a TC).

Thanks again.
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