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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 21 Sep 2011 (Wednesday) 14:26
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Teleconverter for 7D?

 
General_T
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Sep 21, 2011 14:26 |  #1

Hi,

I see TC's for EF Lens, is there any for an EF-S lens?


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cedew
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Sep 21, 2011 14:36 |  #2

I don't think all TCs work with all lenses, might want to look into that. You'll also need to look at taping pins or buying a non-reporting TC if the TC brings light loss down to f/8.




  
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OneJZsupra
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Sep 21, 2011 14:47 |  #3

cedew wrote in post #13140352 (external link)
I don't think all TCs work with all lenses, might want to look into that. You'll also need to look at taping pins or buying a non-reporting TC if the TC brings light loss down to f/8.

I've always had a question about this..... Using a lens the 17-40 f/4 with a TC if it brings the light loss down to F8 will it also had the same effect of the lens being stopped down to F8?

To clear up what I'm asking about is most lenses seem to be it's sharpest around F8. While the light loss is equal to F8 does that also mean you'll have the increases sharpness of being stopped down to F8 or no?

I'm also wondering about the effects of DOF due to having a TC.

Now I guess a simple answer would be whether or not adding a TC actually stops down the aperture (changing the max aperture) or not.

Thanks again and sorry for the noob question.

-Chris


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cedew
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Sep 21, 2011 14:55 |  #4

I've never been super clear on this either. Your aperture is not physically changed, but the light gathering ability is hindered by adding more stuff between the lens and body, roughly equating to a 1-stop loss on your typical 1.4x TC. By the way, one stop from f/4 is f/5.6, f/8 would be 2 stops. You don't have an increase in sharpness just from losing light, which is what a TC does, ignoring the detrimental effects of adding more glass. I don't think you should have an affect on DOF, because again, you're suffering light loss in a different way than actually changing your aperture. All my opinion, could be way off.




  
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LiberationFrequency
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Sep 21, 2011 14:56 |  #5

TCs, in general, are moreso designed for telephoto lenses. Using a TC on a wide lens will show very very noticeable image degradation. Its not like stopping a lens down at all, but rather like adding another element along the line.




  
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Silverfox1
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Sep 21, 2011 15:05 |  #6

theextremist04 wrote in post #13140299 (external link)
They work for all lenses, assuming it's fast enough. EF or EF-S doesn't matter. Your sig says you just have the 17-55, do you actually have a lens worth using a TC with?

Can you please tell the folks what EF-S lenses a teleconverter is compatible with ?


https://photography-on-the.net/forum/showthre​ad.php?t=41922

Regards, Ron ;)


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OneJZsupra
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Sep 21, 2011 16:18 |  #7

cedew wrote in post #13140450 (external link)
I've never been super clear on this either. Your aperture is not physically changed, but the light gathering ability is hindered by adding more stuff between the lens and body, roughly equating to a 1-stop loss on your typical 1.4x TC. By the way, one stop from f/4 is f/5.6, f/8 would be 2 stops. You don't have an increase in sharpness just from losing light, which is what a TC does, ignoring the detrimental effects of adding more glass. I don't think you should have an affect on DOF, because again, you're suffering light loss in a different way than actually changing your aperture. All my opinion, could be way off.

Got ya, Thanks for clearing that up for me, I was thinking that it didn't have the same effects but wanted to be clear. Thanks again.


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phreeky
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Sep 21, 2011 22:06 |  #8

cedew wrote in post #13140450 (external link)
I've never been super clear on this either. Your aperture is not physically changed, but the light gathering ability is hindered by adding more stuff between the lens and body, roughly equating to a 1-stop loss on your typical 1.4x TC. By the way, one stop from f/4 is f/5.6, f/8 would be 2 stops. You don't have an increase in sharpness just from losing light, which is what a TC does, ignoring the detrimental effects of adding more glass. I don't think you should have an affect on DOF, because again, you're suffering light loss in a different way than actually changing your aperture. All my opinion, could be way off.

When you increase focal length but keep the same aperture then your f/stop changes. So yes, your actual f/stop changes, it's not just a reduction in light transmission (although that can also contribute to your exposure, but much less so).

I'm not aware of any TCs that fit EF-S lenses, however plenty will fit APS-C designed lenses from the third party manufacturers.




  
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cedew
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Sep 21, 2011 22:48 |  #9

^^^ Isn't that pretty much what I posted? Just to be clear, the aperture is the physical mechanism of which the f/stop is derived, true?




  
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phreeky
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Sep 21, 2011 23:05 |  #10

cedew wrote in post #13142875 (external link)
^^^ Isn't that pretty much what I posted? Just to be clear, the aperture is the physical mechanism of which the f/stop is derived, true?

Well your post made it sound like it was simply a reduction in light transmission simply because you're placing something between the lens and body, rather than the f/stop changing.

Yes the f/stop is derived from focal length/aperture.




  
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raksphoto
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Sep 22, 2011 00:10 |  #11

General_T wrote in post #13140292 (external link)
Hi,

I see TC's for EF Lens, is there any for an EF-S lens?

I'm going to take a chance, and go out on a limb here ... the general answer is no.

Part of the reason is that EF-S lenses intrude into the camera body further than a EF lens, to create a smaller image circle onto the sensor for (most) FoVCF 1.6X Canon EOS cameras.

That's going to be physically incompatible with TCs.

A secondary reason is that TCs are nominally designed to give telephoto lenses more "reach," and the EF-S line presently does not have a strong showing in the telephoto department. The single one main lens being the inexpensive "thrifty two-fifty," e.g. the 55-250mm.


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EF 135mm f/2L | EF 100mm f/2 | EF 85mm f/1.8 | EF 50mm f/1.2L | EF 35mm f/1.4L EF 100mm f/2.8L IS USM MACRO

  
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General_T
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Sep 22, 2011 08:13 |  #12

Hi,

Thank you all for the responses.

I currently have only the one lens and was just curious about the possibility. I would like to get the CANON EF 70-200MM F2.8L IS II USM LENS (who wouldn't) in the not to distant future and was wondering if a TC would do enough so that I wouldn't be wanting a separate 400mm telephoto zoom lens.


Canon 5D Mk III | 24-105 F4 L IS USM | 100 F2.8 L Macro IS USM | 70-200 MK II F2.8 L IS USM|580 EX II

  
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cedew
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Sep 22, 2011 08:23 |  #13

phreeky wrote in post #13142987 (external link)
Well your post made it sound like it was simply a reduction in light transmission simply because you're placing something between the lens and body, rather than the f/stop changing.

Yes the f/stop is derived from focal length/aperture.

I gotcha, that actually is what I was thinking, placing something between the lens and body is changing the focal length, yes?




  
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mcdevittphotos
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Sep 22, 2011 08:39 |  #14

I have never had too much luck with my 2X teleconverter. I lost all auto focus.


J McDevitt
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Canon 7D, 24-70 L2.8, 70-200L 2.8

  
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nikmar08
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Sep 22, 2011 10:03 |  #15

Using the search feature and reading stickies like the link posted by Ron can be helpful too. I usually find a wealth of information in them!!


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Teleconverter for 7D?
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