question abou telextender with macro lens

paddler4

My standard macro lens is the Canon 100mm L. This lens will not take a Canon telextender directly, but some folks have noted that you can mount the lens on a telextender if you place a 12mm extension tube between the two. I've experimented a bit with a Canon 1.4X II but wonder if anyone has learned more than I have about this.

As a very rough approximation, I found that the combination decreases MWD by about 1 cm. It increases maximum magnification to roughly 1.6:1. One can of course reach this level of magnification with a longer extension, without the telextender, but at the cost of a much shorter MWD. And for a given level of magnification, it gives a greater working distance than the lens alone.

Has anyone experimented to determine the optical quality of this combination? I have no idea what putting empty space between the lens and the extender does to image quality.

Thanks for any information.

Lord Vetinari

paddler4 wrote: »

My standard macro lens is the Canon 100mm L. This lens will not take a Canon telextender directly, but some folks have noted that you can mount the lens on a telextender if you place a 12mm extension tube between the two. I've experimented a bit with a Canon 1.4X II but wonder if anyone has learned more than I have about this.

As a very rough approximation, I found that the combination decreases MWD by about 1 cm. It increases maximum magnification to roughly 1.6:1. One can of course reach this level of magnification with a longer extension, without the telextender, but at the cost of a much shorter MWD. And for a given level of magnification, it gives a greater working distance than the lens alone.

Has anyone experimented to determine the optical quality of this combination? I have no idea what putting empty space between the lens and the extender does to image quality.

Thanks for any information.

I doubt the extension tube will affect the IQ. If you find the setup useful just try using it for a while.
Brian V.

paddler4

Brian,

Thanks. I'll do that, although at first I will probably try it only when I have time to do similar shots without it, just in case.

Dan

basflt

i dont doubt , im sure , the tube wont effect IQ , you could add more if you like

the extender will effect IQ slightly
dont know how much as i dont own Canon

i tried a similar setup w Nikon in the past , and had no complains

paddler4

i dont doubt , im sure , the tube wont effect IQ , you could add more if you like

I often use tubes in the standard position, behind the lens, so I understand their effects there. What puzzled me is placing them in front of an extender. Since the extender acts like an additional group of lens elements, this is placing the tube(s) between groups of lens elements. I don't think I have ever seen a technical discussion of this.

ziggy53

Teleconverters/tele-extenders are designed to be used with lenses which have a narrow angle of convergence. Primarily, this means true telephoto lenses through super-telephoto lenses. A few notable exceptions are the 70-200mm zooms with constant aperture (which also have a relatively narrow angle of convergence.) (In the case of Canon lenses, the EF 100-400mm f/4.5-5.6L IS USM is also considered "compatible", but only marginally acceptable IMO.)

While the Canon EF 100mm f/2.8 L IS USM Macro is not approved by Canon for use with its teleconverters, it is "safe" to use if you add at least the 12mm extension tube, as mentioned by paddler4 in the first post of this thread.

I believe that you can expect "some" (as in, "a little bit of") color misalignment (chroma aberration, CA) in the borders and corners and at large apertures, compared to not having the 1.4x teleconverter. Whether this is acceptable depends upon the subject, and whether you apply software correction in post.

Likewise, at large apertures and working with flat subject matter, you can expect softer corners as some field curvature sneaks in. Stopping the aperture down should alleviate some of the problems.

A 2x teleconverter will be more pronounced with problems than a 1.4x teleconverter.

All teleconverters will soften the image slightly "and" reduce contrast, although some lens/teleconverter pairs fair better than others, and only testing will prove whether a particular lens/extension/teleconverter works for your application and quality requirements.

paddler4

Ziggy,

thanks. Very helpful.

I'll try to find time to do a few test shots, with and without the telextender, to get some A/B comparisons. My handheld macro work is usually around f/13, which should help.

Dan