Canon 2xEF II and 1.4 II staked together

[phillane]

I remember reading somewhere about using these two extenders together and maintaining AF on a canon 300 EF 2.8 USM IS. Any one have any tips or experience in this area?

[Alfred Forns]

Hi Phil Just stack them together I used to use them on my 500 & 600 Remember you got lots of magnification and need the shutter speed !!!

I don't have Canon any more and do miss that feature, with Nikon you can not stack. btw they only fit in a particular order, don't recall !!! btw with a pro body you do maintain AF at f4.0 !!!

[Doug Brown]

They can be used together and maintain AF on 1-series bodies only. You will not get AF with the XXD or Rebel series. The only way they fit together is in the following order: body, 1.4x, 2x.

[Steve Canuel]

I use stacked TCs with my 40D and 400 DO quite frequently (mostly because I like the challenge). Combo does not AF though. Of course image quality depends on personal preference and intended use but I've gotten a few that enlarged nicely to 8x10 prints. I do tend to process these images on the softer side but I have a preference for that anyway. I just posted a stacked TC image in the Avian forum (RWBB).

[Magnus Thornberg]

The autofokus works for me pretty good in good lightning! I have 40D EF300/2.8L IS USM with stacked Soligor 1,4x and Canon EF 2x MkI. It even worked in this weather!

http://www.fotosidan.se/gallery/view...587996&target=

But the sharpness isn´t 100%!

/Magnus

[Jasper Doest]

Sharpness can be good when you stop down to f/11 of f/13, but you'll lose a lot of light doing that. AF works on 1D serie bodies, but is SLOW!

[Andy Wai]

They can be used together and maintain AF on 1-series bodies only. You will not get AF with the XXD or Rebel series. [...]

The way a reporting TC works is it tells the lens "you have a TC of this strength behind you". Then the lens tells the camera. If you look carefully, a Canon TC has 3 extra reporting pins on the lens side compared to the camera side. That also means it can tell the lens in front of it about itself, but it won't listen to another TC behind it. Therefore in a stack, the lens only knows of the TC right behind it and report that to the camera. In the case of 500/4 with a stack, the camera see 1000/8. For 300/2.8, the camera sees 600/5.6. So the former won't AF on non-1 series boides but the latter should be able to.

Don't have the 300/2.8 but on a 500/4, AF is crawling slow with the stack, even on a 1 series body. So I don't use it for anything but moon shots: a 500 with stack gets me close to frame filling moon shot on a 1.6x crop body. Since moon shots are normally done with manual focus anyway, no AF is a moot point.

Andy

[phillane]

Some shooters have suggested scotch taping three contacts for advanced focusing benefit however I hesitate to do so. Anyone hear of this or perhaps have tried this?

[Andrew McCullough]

My 20D had autofocus (very slow) with this combination. If I remember right, the camera only detected 1 TC.

Sorry, Andy W already said this.