1.4 and 2x Extenders

[dave henri]

I recently purchased both the 1.4 and 2x extenders. I noticed that

you can mount the 1.4 to the camera, then the 2x, then the lens, but

not the other way around, (2x to the camera). When I do this I only

see 2 stops reduction, not 3, as I should. Does anyone know if this

is proper use of the extender combo? I've read otherwise where a 12mm

extension tube was placed between them, but they seemed to fit just

fine as is.

 

I appreciate all comments.

[dglickstein]

According to the manuals, you attach the extenders to the lens first and then attach it to the body--do not attach the extender to the body without the lens.

 

dG

[bobatkins]

The older TCs needed the 12mm extension. The new (II) TCs don't - as long as you stack them in the right order.

 

Whatever the camera says, you get 3 stops reduction with stacked 2x and 1.4x TCs. The camera should compensate exposure automatically, even if the readout is wrong.

[robin_sibson1]

Dave, you have already realised that you can only combine the Extenders in the order Camera-Extender1.4x-Extender2x-Lens. This can be done with either the original Extender1.4x or the Extender1.4xII, but only with the Extender 2xII. If you use the original Extender2x you need a short extension tube between the Extenders and are liable to lose infinity focus, but that is not required with the Extender2xII, which has a different optical design.

 

Extender-compatible lenses have three extra pins on the back, and the Extenders have three matching pins on the front. The pin closest to the normal pins is a common pin. In the Extender, one or both of the other pins are connected to it; that's ALL that happens in the Extender. This gives three possible combinations. The Extenders use two of these combinations, the third is used by the Life Size Converter, which connects to the 50/2.5 macro lens in the same way. When an Extender is put on a lens, and then the lens is put on the camera, the lens polls the connections from the common pin to the other two extra pins for open/closed circuit, and deduces from this which Extender is fitted, if any (all open circuit = no Extender). It then adjusts its aperture and focal length reporting and its AF parameters to suit.

 

If you stack Extenders, then the lens will recognise the Extender2x, but there is no way that the Extender1.4x can be recognised (there are no extra pins on the back of the Extender2x, and even if there were the open/closed circuit logic has no spare option that it could use to report stacked Extenders to the lens), so the lens will report its focal length as multiplied by 2.0 not 2.8 and its aperture as reduced by 2 stops not 3. However, TTL metering will still work, because at the apertures you are now talking about no full aperture correction is needed. If you start with a fast enough lens on a capable enough camera body, AF will still work, and the presence of the Extender2x will slow the AF down to a point where no extra correction for the additional presence of the Extender1.4x is needed.

 

Stacked Extenders are known to be workable, but in addition to the reduced maximum aperture there is also a significant loss of optical quality, so it is probably not a good idea for regular use.

 

To the camera, a lens+Extender combination is simply a different lens. My 135/2 on the Extender1.4x is seen by the camera as a 189/2.8, for example. However, the camera sees an Extender on its own as an alien life-form, and will usually lock up if the shutter is fired. That's the reason why it is normally recommended to fit the Extender to the lens and then put the combination on the camera.

[bill_goldman]

Obviously, Canon does not recommend stacking extenders and therefor has not implemented a scheme to have the camera recognize the combination. The detailed comments above tell the whole story.

[mark_chappell]

What Robin says. With stacked extenders, IS will continue to function (if it's an IS lens), but

you will lose AF if the lens speed is slower than f2 (with most cameras) or f2.8 (with the 1D

series, the EOS 3, and the 1v). You can always manually focus but due to the rather dim view

from the loss of 3 stops, this can be a challenge. I avoid stacking converters as a general

principle, but every so often I'll do it for a very distant subject (this is always with a 500/4 IS

lens). IF I manage to focus correctly, I think the results are slightly better than what I'd get if

I just used a 2X extender and then cropped -- but not a lot better. And often I don't nail the

focus even though I 'bracket' focus (focus, shoot, intentionally defocus and refocus, shoot,

etc.).

[david_ceruti]

Robin

 

Great comprehensive answer! One of the reasons I spend so much time on this site

 

Thanks

 

David Ceruti

[dave henri]

Robin,

 

thank you very much for the comprehensive answer. It explains the non-recognition of the 1.4 teleconverter when placed behind the 2x. I don't usually stack them, but was fooling around with the combination of the two extenders and the lens, checking the difference in aperture reporting.

 

I guess another way to compensate with the stacked teleconverters is simply to apply some exposure compensation to keep the histogram in proper position, and just use the same exposure comp on a film body once you understand the adjustment when using this lens setup.

 

Thanks again.

[robin_sibson1]

Dave, to a first approximation you should not need any exposure compensation; the TTL metering will take care of it. Only if you are using a separate meter do you need to compensate for the fact that with stacked Extenders the reported aperture is incorrect.

 

There is a more subtle effect: when you use a wide-aperture lens the metering system may not be able to 'see' all the light coming through it, and compensation may be necessary. For details of this, read, for example, Geoffrey Crawley's articles in the BJP about the metering system in the Canon F-1, when full-aperture metering was new and exciting. However, this compensation is not needed below about f/4, and you are quite safe when using stacked Extenders!