Teleconverter and extension tube together?

codrus

What happens if you put an extension tube between a teleconverter and a lens? Does it irretrievably screw up the image, or will it focus? Presumably it's not useful as a focus-to-infinity lens, or they'd do that instead of having the teleconverter only work on lenses with a recess in the back, right?

--Ian

ziggy53

codrus wrote:

What happens if you put an extension tube between a teleconverter and a lens? Does it irretrievably screw up the image, or will it focus? Presumably it's not useful as a focus-to-infinity lens, or they'd do that instead of having the teleconverter only work on lenses with a recess in the back, right?

--Ian

I don't know of a lens that will focus to infinity "while" using an extension tube.

Extension tubes mess with the geometry of the subject vs image plane. Some lenses are really only designed to accurately focus at a fixed distance from the image plane. Those lenses will typically produce optical distortions and/or color aberrations when used with extension tubes or incompatible teleconverters. Zoom lenses are particularly vulnerable.

The problem is that of "convergence". Complicated lens designs typically only converge the image at a fixed distance to the image/film plane.

"True" macro lenses are typically fairly accommodating of both extension tubes and compatible teleconverters.

Diopter close focus lenses are typically better to use on complicated zoom lenses than using extension tubes. Some longer zooms are also compatible with teleconverters. I use both the Canon EF 70-200mm, f2.8L USM and the Canon EF 70-200mm, f4L IS USM with a 500D diopter close-focus lens and, occasionally, an EF 1.4x II teleconverter.

When the lenses are set at infinity, both lenses yield very nice close-focus and near-macro images. Focussing the lens to closer distances allows higher magnifications but with some loss in image quality and reduced distance to the subject.

One of the nice things about using a 500D diopter is that, when the lens is set at infinity, you maintain a 500mm working distance from the subject. This allows ample distance for arranging the flash(es) as well as not spooking insects (or getting too close to the dangerous ones).

ziggy53

Sorry, after reading your question again it appears I misunderstood.

Using an extension tube "between" a lens and a teleconverter is possible and some folks use that method to allow the use of a teleconverter on a lens which is otherwise physically incompatible. It does reduce the distance to subject at infinity setting and usually degrades the edges and corners of the image. Sometimes the net result is OK for the combination but it really depends a lot on the "particular" lens and teleconverter combination used.

At any rate, only a short extension tube is typically used.

codrus

ziggy53 wrote:

Sorry, after reading your question again it appears I misunderstood.

Using an extension tube "between" a lens and a teleconverter is possible and some folks use that method to allow the use of a teleconverter on a lens which is otherwise physically incompatible. It does reduce the distance to subject at infinity setting and usually degrades the edges and corners of the image. Sometimes the net result is OK for the combination but it really depends a lot on the "particular" lens and teleconverter combination used.

Thanks Ziggy, that was indeed what I was asking.

FWIW, I just tried it with my Canon 1.4x TC and (just arrived!) Kenko tubes. The 12mm tube isn't quite long enough to separate the TC from the various non-TC-compatible lenses that I have, and with the 20mm they won't focus out to infinity, so it looks like none of my other lenses are useful that way. (Sigma 50-150, Canon 50/1.8, 17-55, and an old cheap 75-300 non-IS)

I hadn't actually planned on using it that way (the TC is for my 70-200) but was just looking at the various bits sitting on the desk and started wondering...

--Ian

Photoskipper

Putting an extension tube between the TC and lens is do-able but no AF and the focal lenght is very limited for all the lens I tried.

Here is one of the old lens - 70-300 for example.