teleconverters( new title so maybe someone can tell me)

[jann1033]

is there an appreciable difference between the image quality of kenko or sigma or tamron vs canon when used on a rebel xt? any pros or cons for either( except price)

also on the kenko website it says with the 1.4 you'd lose one stop and need at least f4 lens...on sigma and tamron it says for there 1.4 you need at least f2.8 lens...anyone know why? so the f4 70-200 wouldn't work with tamron or sigma?

also has anyone ever used them for macro( as it suggests on the kenko site) i like the lens i have but not the adapter to make it 1:1( not sure if it's me or the adapter that has the problem) so i was wondering what a 1:1.4 ratio( or what ever it would end up being,) would look like

 

[MarkBarbieri]

There is a quality difference between the Canon and the off brands.

With a 1.4x teleconverter, you will lose 1 stop of light. That's a basic rule of optics, not something that converter makers can do something about. Because most consumer DSLRs cannot autofocus reliably beyond f/5.6, you can't use a 1.4x teleconverter on an lens slower than f/4.0. If you did, the autofocus mechanism wouldn't have enough light to work with.

Some of the off-brand teleconverters cheat. They pass along the information from the lens without telling the camera that they are there. In those cases, the camera doesn't know and will continue to try to autofocus beyond f/5.6. If you are looking at something with enough contrast, the autofocus may work. I've been told that you can make the Canon teleconverter cheat the same way by taping over one of the electrical contacts.

The restriction to f/2.8 sounds to me like it is coming from someone selling a 2x teleconverter. In that case, you lose two stops. Once again, the result of using a 2x teleconverter on an f/2.8 lens is an f/5.6 lens.

One other thing to be aware of is that the Canon teleconverters protrude into the lens a bit. They will only work with lenses designed to accept them. that is generally all of the wider aperture telephoto lenses that Canon sells. I don't think that you can use a Canon telecoverter on your 28-135 lens regardless of f-stop because it physically won't fit.

Another thing to be aware of with teleconverters is that they magnify all of the deficiencies of your lens. I have both the Canon 1.4x and the 2.0x teleconverters. When I pair them with my 70-200 f/2.8 lens (which is a very nice lens from an optical standpoint), the 1.4x still looks good, but the 2.0x shows very noticable image degradation.

 

[0bli0]

a little bit more info... Canon teleconverters only work with certain 'L' lenses. on the otherhand, the Kenkos work with all lenses. as Mark pointed out, where a maximum apeture is greater than 4.0 (or 5.6 on a 1 series body), auto-focus does not work - and that's regardless of what brand of TC used.

there are many different brands of teleconverter - including Canon and Kenko (the Tamron is made by Kenko as well). Kenko/Tamron have 2 different ranges. there is the standard black ones which only have (from memory - i'm too lazy at the moment to look it up) 5 elementt groups. they also have a pro/SP range (white) which has 7 elements. this one is visibly much better than the standard one, although the 2.0x version is still pretty soft and loses 2 stops of light (again as Mark said).

sorry i was going to say more but i just spent 9 painful hours in Apia, Samoa and another 6 or so in Honolulu because our plane caught fire getting here - plus the 16 hours of air travel. i've forgotten what else i was going to say. if i remember in the morning i'll continue.

 

[jann1033]

yikes about the plane..that would be one scary flight

i am guessing all the other electronics would work, just not the focus? i noticed the 2 different versions

thanks

 

[0bli0]

yeah it was kinda scary - especially when we hit turbulence during the emergency landing. the landing lights illuminated the clouds so it was suddenly bright and the plane was shaking violently. people started screaming.


yes, all of the other functions - aperture, etc. work fine.

 

[MarkBarbieri]

i just spent 9 painful hours in Apia, Samoa and another 6 or so in Honolulu because our plane caught fire getting here - plus the 16 hours of air travel. i've forgotten what else i was going to say. if i remember in the morning i'll continue.

I'd like to go to Hawaii, but not quite like that.