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Using EF extenders with non-EF long lenses


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Earlier this week, a thread called <a


msg_id=00Ezae&tag=">Long Glass --> Nikon Manual Focus Lens + Nikon-to-

EOS converter + Canon 2X II</a> made me aware that you can't use non-

EF lenses on an EF extender, even though you can use the same lens

(with appropriate adapter) on the body without the extender. It

seems that the presence of an EF Extender requires a recognized EF

(or EF-compatible) lens in order for the EOS camera to work

properly. Well, this was a challenge to me, as I recently bought a

Nikkor*ED 400/3.5 lens for use on my 20D with 1.4x and 2x Canon

extenders. So, after pondering things for a while, I made an

insulating annulus, or ring, out of matte-finish acetate sheet

plastic (used for drafting and etc.) which fits inside the 20D body

and covers the contact points so that they don't connect with the EF

Extender. I made a few test shots on my 20D with a Tamron SP 300/5.6

on a Canon Extender EF 1.4x and it works like a charm.


<p>For a 20D, the outer diameter of the insulating ring is 53.5 mm

and the inside diameter is 42.5 mm. The ring fits snugly inside the

20D body just below the mount assembly and covers the lens

contacts. Since it fits evenly all of the way around the inside of

the mount barrel, you don't have to worry about it slipping out of



<p>This also works on an Elan 7 (EOS 30) full frame film body, but

the outer diameter of the ring should be a bit larger to give a snug

fit. You may suspect that since the inner diameter of the insulating

ring (42.5mm) is less that the diagonal of the full frame image

(44mm) that this solution would cause vignetting, but I don't think

so. The attached photo shows the insluating ring lying on an

Extender 1.4x. Since the ring does not cover any parts of the

extender's rear element, it should not be in the optical path.

Similarly, the ring should not cause a problem with internal flare,

but only experience will show if this is true. Note that the photo

shows the ring lying on top of the 1.4x extender, but the ring

actually goes inside of the 20D body, not between the body and lens

mount surfaces (I can't show a picture of this, as I can't figure out

how to get the 20D to take a picture of itself without a lens on

it). Also, the 20D-sized insulator ring fits nicely inside a set of

58mm filter stacking caps, which is where I'll keep mine (I cut four

of them in about 15 minutes) while I'm out stomping around with my

big glass. I'm not sure how well this approach will work in the long

run, but it's a step in the right direction. Now, if I can only sell

enough photos to afford some really big glass that doesn't need this

kind of kludge (600/4 L, here I come...).


<p>If I have a chance, I'll try to write up a more detailled

description with better pictures and post it on my site - I'll let

you know. I can hardly wait to get my Nikkor*ED 400/3.5 back from

the clinic (not to mention my recently squashed 70-200/2.8 L IS).

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One of the biggest reasons not to use an EF extender with a lens which it isn't designed for is because of the protruding front element. All of the big Canon glass has a deeply recessed rear element which allows for clearance of the extender. I imagine that your 400/3.5 may be similar in this respect. Be careful which lenses you try to use this on. If the rear element on the lens isn't recessed far enough, you could ruin both extender and lens.



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Jim, understood. The protruding front element for long lens teleconverters is common to Pentax, Nikon and Canon (plus probably other brands as well). The Tamron SP 300/5.6 fits both EF extenders with no problem, even though it's a relatively slim lens. One of the main reasons that I felt comfortable getting the Nikkor*ED 400/3.5 is that the Nikon teleconverters which are designed to work with it have effectively the same front element geometry as the Canon extenders (and the Pentax "L" teleconverters, too).
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Even if the EF converter doesn't quite fit, you can insert a slim extension tube between

converter and lens. With a 400 mm, you might (?) still be able to focus to infinity, depending

how how much 'slop' there is in the lens infinity focus (many ED lenses will focus 'past

infinity' to allow for thermal expansion, etc.). For subjects reasonably close, 12 mm of

extension will be perfectly fine.

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James, this is an ingenious way of dealing with the same problem that leads to the recommendation to fit Extenders and extension tubes to the lens first, then fit the whole assembly to the camera body. Since not everyone may be aware of what the problem is, here's the background. If you fire the shutter on an EOS body, whether film or digital, it completes its cycle with no lens attached, or with a lens attached, but NOT if there is only an Extender or extension tube attached with no lens, in which case the shutter locks up. This is what a former colleague of mine calls 'a design feature of negative utility'. The camera is unaware of the presence of your lens on its own, so fires properly without the Extender, but with the Extender it recognises that the Extender is fitted but again thinks there is no lens, and to prevent it from locking up you need either to prevent it from recognising the Extender, which is what you have done, or to reassure it that a lens is indeed present, which is not a viable solution unless you are a third-party manufacturer with a good guess about the electronic requirements and the wherewithal to implement them.
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Sounds like a great idea.


I had tried taping the 1.4x's pins, which did not work, like I said in the other thread, but I did not want to mess with taping the pins in the camera.


Let's hope the 400mm 3.5 works well optically with the EF 2x. So far info around the net said its best companion is the Nikon TC-300 or 301, rather big and cumbersome to carry around, not to mention adding much more length and shake problems.


The 400mm 3.5 is about as much weight and size I'm willing to lug around. No 600mm f4 for me.

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Nam, I also hope it works well with the 2x Extender. 400mm x2 x1.6 = 1280mm equivalent angle of view on a 20D; should be great. I often used a SMC Pentax 500/4.5 with 2x teleconverter on Pentax film bodies, but it had too much CA on the 20D, so I sold it. I really miss having the reach, so the 400/3.5 on 20D should keep me happy for a while.
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You can defeat the problem of EOS bodies recognizing the TC and locking up if there is no EF lens attached by not fully rotating the TC into the locked position.


The danger here is that the the lens and camera are not locked together to there's a danger of then coming apart if they rotate.


However it's a "quick fix" if you find yourself trying to mate, for example, an EOS body with a TC attached to a telescope or an EOS body with TC attached to a manual focus lens adapted to an EOS mount.

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Nam, the SMC Pentax 500/4.5 and 400/5.6 ("K" version) are both manual aperture lenses, and so don't have the aperture control lever which has to be removed from virtually all other K-mount lenses (as they have auto apertures). I continue to use a very sharp SMC Pentax 18/3.5 which had a successful leverectomy. This has probably lowered its resale value for Pentax users, but would be neutral or perhaps beneficial for Canon users. A recent posting on <a href="http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00ExzY">Conversion pieces for old M42 thread lenses</a> includes a brief description of the two ways to mount Pentax-K lenses on EOS bodies (in both cases, the aperture lever must be removed, if present).


<p>I think the Pentax-K "gems" of interest to EOS users should include the 15/3.5, 18/3.5 (which I have), A* 85/1.4, A* 135/1.8 and A*ED 200/4 Macro. The Pentax-A*ED 85/1.4 is about the same price as the Canon EF 85/1.2 L (both in used Mint condition), and a used A* 135/1.8 is generally quite a lot more expensive that the EF 135/2 L, so I'm not sure that it makes sense to buy them, but they are certainly "keepers" if you have them before getting into EOS. The A*ED 200/4 Macro has an absolutely magnificent reputation, and goes for about the same price as a new EF 180/3.5 L. I also use a few older SMC Takumar lenses on my 20D with generally fine results, including the 50/4 macro, 85/1.8, 100/4 bellows, and 135/2.5. In the long term, I plan to replace the 85 and 135 with a Carl Zeiss (Contax) Planar T* 85/1.4 and a Canon EF 135/3 L, but I'll probably buy a second 20D body first. The 50/4 macro is a fine backup to my EF 100/2.8 USM macro, and quite a bit smaller if you have to travel light.


<p>Bob, the insulating ring that I describe allows you to mount and use non-EF lenses on an EF extender without "backing off" the mount and without using an extension tube or spacer. It allows you to fully lock the lens and extender on the camera and get the camera's normal behaviour for non-EF lenses, exactly as if the extender were not present (except of course for the increase in effective focal length).

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