Stacking 2.0 & 1.4 Teleconvertor with 12mm ext tube

[LarryS1]

I have an EOS7dii, with my 100-400mm canon lens I attached a 2.0 tc with a 12mm lens tube to a 1.4 tc.  The first time, no problem, second time lens doesn't seem to focus at in manual focus.  The lens & teleconvertors are all Canon gear.

Any suggestions?

[Waddizzle]

I suggest that you forget the idea of using the 2x teleconverter and the macro tube together.  In fact, I suggest that you forget the idea of using either one of them with that lens.  Buy a real macro lens, instead.

Why is it that you cannot focus on anything?  Physics.  A macro tube reduces the MFD, minimum focusing distance, by sacrificing your ability to focus the lens at infinity.  But, if all you are trying to do is focus on something very small and close to the camera, what difference does it make if you cannot focus out to infinity?  None, it does not make any difference.

Except, if a little is good, then more is not always better.  By adding the 2x TC, you have probably magnified the 2x teleconverter's effect to the point where the MFD is probably INSIDE of the lens barrel.  Remember, MFD is measured from the image sensor, not the end of the lens.

[LarryS1]

I was trying to extend my zoom lens, by adding the 2.0 & 1.4 tc, in a series to my lens.  I was told that could be done by attaching the ext tube to allow both teleconvertors to connect to each other.  What's strange is it worked the first time I tried it, when I went in the field to  try it, the lens wouldn't focus.  

[wq9nsc]

The 100-400 is a slow lens with variable aperture from 4.5-5.6  and even the 1 series cannot use AF with the very high minimum aperture created by this lens with stacked converters. 

Using two in combination EVEN with a very good sharp prime will result in a tremendous loss of IQ and to AF with two converters on a lens you would need a fairly fast lens on a 1 series body.

Rodger

[kvbarkley]

Doing things like this quickly leads to diminishing returns, if not negative returns. While one Canon TC is probably effective, adding anything else is probably no better than cropping.

[Peter]

I tried 2xIII+12mm macro tube+1.4II+300/2.8L IS+M5. It works, even when focusing to infinity or the moon. The image quality is "OK" at short distance like 20 meters.

[LarryS1]

Peter, thanks for trying and letting me know it worked for you.  I had tried it a week ago, and I was able to focus on distant objects.  Then went out this last weekend for the purpose I intended on, I couldn't get any of the lenses I tried (24-70, 70-200 or my 100-400).  I wish I could figure out what went wrong with the camera.

i really appreciate your efforts and response,

[Peter]

Perhaps lack of light.
Have you tried Live view?

[ebiggs1]

Years, and years ago I tried to use a 1.4x, a 2x and a 3x tel con stacked together on a FD 300mm f4 lens.  I found out quickly it was a horrible idea.  I suspect you will come to the same conclusion..................soon, I hope.

IMHO, the use of any tel-con or x-tube is a bandaide fix for a problem that requires the proper lens alone.

[RobertTheFat]

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@ebiggs1 wrote:

Years, and years ago I tried to use a 1.4x, a 2x and a 3x tel con stacked together on a FD 300mm f4 lens.  I found out quickly it was a horrible idea.  I suspect you will come to the same conclusion..................soon, I hope.

Quite so.

IMHO, the use of any tel-con or x-tube is a bandaide fix for a problem that requires the proper lens alone.

I don't althgether afree. My 70-200mm f/2.8 tolerates the 1.4x III quite well, I think.

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