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Thread started 23 Jul 2010 (Friday) 19:26
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AF with 2x TC?

 
The ­ Ran
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Jul 23, 2010 19:26 |  #1

I'm going to town tomorrow and the camera store had a 2x TC for £40 and if it's still there I'd like to buy it. My questions are will my 20D be able to focus with it? I'll be using it with my 70-300mm f/4-5.6, so that would make it f/11 at the long end. Will it be limited to really good light, or will it just flat out refuse to focus? Obviously I'll try it out before I buy, but of course I won't be able to take it out of the store and the lighting conditions out of the windows might not be too great.

I've heard, maybe erroneously, that the Canon 2x TC purposely tells the camera not to focus but a non-reporting TC still allows focussing. I can't remember what make this TC is but it's not Canon.

Another question I have, although perhaps more suited to the lens section, is will a cheap converter substantially affect image quality? Note that I'm not using L glass here.


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Gary2027
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Jul 23, 2010 20:39 |  #2

No, it will not AF. You would need a f2.8 lens in order to use the 2x converter with your 20D.

When people talk about non-reporting TC's, they usually mean the 1.4x converters which they use with f5.6 lenses. I used to have a Tamron TC like that. As a general rule they work well with the sharpest of zooms, and the prime lenses.

On a lens like the 70-300, it might look just OK, but I'd bet most people would not be very happy with those results. People tend to use them most with the 400 f5.6 prime which is quite sharp to begin with, and can hold up with the teleconverter. As you can imagine though, it works best in very good lighting so the AF system has plenty of contrast.




  
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sandpiper
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Jul 23, 2010 20:58 |  #3

The Ran wrote in post #10592288 (external link)
My questions are will my 20D be able to focus with it? I'll be using it with my 70-300mm f/4-5.6, so that would make it f/11 at the long end. Will it be limited to really good light, or will it just flat out refuse to focus?

All bodies bar the 1D require f/5.6 or faster lenses to AF properly (the 1D can manage down to f/8 ). A slower lens does not necessarily mean that it won't AF but that it is going to struggle to find sufficient light to do so. If you are shooting in strong sunlight, it may well work fine but with less light it will suffer from slow AF or may hunt quite a bit before finding focus, or may not work at all.

In your case, you will be two stops outside the official limits for AF so I would hazard a guess that AF is going to be unlikely to work, or hunt like mad if it does make an attempt.

The Ran wrote in post #10592288 (external link)
I've heard, maybe erroneously, that the Canon 2x TC purposely tells the camera not to focus but a non-reporting TC still allows focussing. I can't remember what make this TC is but it's not Canon.

That is correct in that a Canon TC will not attempt to focus past f/5.6 on your camera, a non-reporting TC will attempt to focus, but at f/11 you are really pushing the boundaries.

Note that a Canon TC can be turned into a non-reporting TC by simply taping over some pins.

The Ran wrote in post #10592288 (external link)
Another question I have, although perhaps more suited to the lens section, is will a cheap converter substantially affect image quality? Note that I'm not using L glass here.

Sorry, but yes it will substantially affect image quality. Even a top end 2x TC, on L glass, will show a little deterioration in IQ - a cheap 2x TC on a cheapish lens will be very noticeable. I have a Canon 2x TC and it works great on my 300L f/2.8 with minimal IQ loss, however bolt it to the back of my 100-400L and things get fuzzy pretty quickly. I will use the 1.4xTC on the 100-400L but not a 2x, even a really good one.




  
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The ­ Ran
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Jul 23, 2010 21:33 |  #4

Well that's a shame, no point me bothering with it then. I was just after a cheap way to replace my ****ty 400mm. I'll have to ask them if they have any 1.4x TCs instead making it 420mm and f/8 so it's got more chance of focussing (or is that still not a good idea on a 20D?), or I could tear apart the 400mm and somehow find a way to adjust the aperture manually.


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lannes
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Jul 23, 2010 23:28 |  #5

The Ran wrote in post #10592805 (external link)
Well that's a shame, no point me bothering with it then. I was just after a cheap way to replace my ****ty 400mm. I'll have to ask them if they have any 1.4x TCs instead making it 420mm and f/8 so it's got more chance of focussing (or is that still not a good idea on a 20D?), or I could tear apart the 400mm and somehow find a way to adjust the aperture manually.

I don't think the Canon 1.4x and 2.0x extenders will work on the 70-300 zoom, they require the lens to have a recessed rear element.

Check out the list of compatible lenses

http://en.wikipedia.or​g/wiki/Canon_Extender_​EF (external link)


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MOkoFOko
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Jul 24, 2010 02:01 |  #6

Any 1.4x or 2x TC for $40 or 40 quid... is likely JUNK. There are only two TC brands/models worth getting, and they're 4x-6x as expensive ;)

I don't even need to know what model they've got in that shop... it's obviously going to SERIOUSLY degrade IQ--that price is a dead giveaway. You don't get stellar optics at bargain-basement prices.


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yogestee
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Jul 24, 2010 02:03 |  #7

MOkoFOko wrote in post #10593743 (external link)
Any 1.4x or 2x TC for $40 or 40 quid... is likely JUNK. There are only two TC brands/models worth getting, and they're 4x-6x as expensive ;)

I don't even need to know what model they've got in that shop... it's obviously going to SERIOUSLY degrade IQ--that price is a dead giveaway. You don't get stellar optics at bargain-basement prices.

and which ones are they??


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MOkoFOko
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Jul 24, 2010 02:06 |  #8

yogestee wrote in post #10593749 (external link)
and which ones are they??

The Canon TCs and the Kenko Pro300 DGs. The DGX's have major compatibility issues and aren't recommended. The sigma TCs are just plain disappointing...


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yogestee
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Jul 24, 2010 02:17 |  #9

MOkoFOko wrote in post #10593753 (external link)
The Canon TCs and the Kenko Pro300 DGs. The DGX's have major compatibility issues and aren't recommended. The sigma TCs are just plain disappointing...

What about Tamron SP 1.4X (the white model)??


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Jul 24, 2010 02:35 |  #10

yogestee wrote in post #10593779 (external link)
What about Tamron SP 1.4X (the white model)??

I seriously looked into that one at one point to better match my 70-200mm... It's impossibly hard to find, and the used ones that pop up seem to be 80% Nikon. They sell for more than the Kenko pro300 dgs as well--so not worth really mentioning. The 300 dgs are just as well built, they're a newer design, and they're slightly cheaper (keaphoto--$147 shipped).

The only tests I've seen have the SP about on par with the original Kenko pro300 (precursor to the pro300 DG). Definitely not bad, just.... rare. I'd like to have one myself--but if I really want a white one to match my L lens, I may as well get the weather-sealed canon for $100 more!!!


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Jul 24, 2010 02:39 |  #11

the one & only 2x TC that I ever bought was so bad, I removed the optics in it and only use it as a macro extension tube.


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lannes
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Jul 24, 2010 04:03 |  #12

MOkoFOko wrote in post #10593814 (external link)
The only tests I've seen have the SP about on par with the original Kenko pro300 (precursor to the pro300 DG). Definitely not bad, just.... rare. I'd like to have one myself--but if I really want a white one to match my L lens, I may as well get the weather-sealed canon for $100 more!!!

Do you mean these pieces of junk, their just rebranded kenko's

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Jul 24, 2010 05:53 |  #13

lannes wrote in post #10593932 (external link)
Do you mean these pieces of junk, their just rebranded kenko's

QUOTED IMAGE

Ever used one??

I've owned the SP 1.4x for around five years.. They are far from junk!!

Note- They've been around for years and probably not rebranded Kenkos..


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Jul 24, 2010 11:07 |  #14

yogestee wrote in post #10594097 (external link)
Ever used one??

I've owned the SP 1.4x for around five years.. They are far from junk!!

Note- They've been around for years and probably not rebranded Kenkos..

These are my Tamron's, I don't find them as sharp as the Canon extenders, I've been trying them on the 135L and the 200 f/2.8L and I'm not getting as good results as the full canon combination.

I guess the real advantage is that you can use them with any lens, as they don't have a protruding front element like the Canon's do.

They do however do look like the Kenko, even down to the vertical body cut outs.

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Even the rubber grip pattern (large squares) on the 2.0x Tamron is the same as the Kenko grip pattern

This article discusses that the Tamron TC's are made by Kenko for them and are just rebranded.
http://www.camerahobby​.com/Access-LensAccessories.htm#2 (external link)

So don't pay more the Tamron version unless you like the off white finish.

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Jul 24, 2010 11:12 |  #15

lannes wrote in post #10594944 (external link)
These are mine, I don't find them as sharp as the Canon extenders, I've been trying them on the 135L and the 200 f/2.8L and I'm not gettng as good results as the full canon combination.

I never got one to test, but I wouldn't doubt if that's right. They have been compared to the pro300 (pre-DG)--and indeed, people said they had identical optics. The jump from the pro300-->pro300dg was supposedly an optical improvement, with the pro300dg-->pro300dgx being exactly the same.

In the lone side-by-side comparison I saw, the Canon TCs and Kenko Pro300DGs had the same IQ. It's pretty much echoed by everyone else who weighs in on the topic.


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AF with 2x TC?
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