[littledrawe]

The 1.4x-L & 2x-L rear converters were only made for some lenses because the front element of the converter sticks out beyond the mount. Can you add a length of extension tube to the front of the converter to take up the space around the protruding front element and then attach it to your lens to make it fit with the lens you want to use it with?
As I understand it whatever length of extension tubes you use will decrease the minimum focusing distance as well as prevent you from focusing to infinity. Will the extension tubes have any other effect?

[jatrax]

Loss of light. And with the tube and the TC you might be losing so much it is not worth it. Also, any communication between lens & camera assuming the tube does not have contacts. But that is an interesting thought. Try it and let us know if it works.

[bdparker]

My understanding Teleconverters and extention tubes and not the same thing.
Most Extention tube have no connectors and therefore you lens will become a manual lens and they increase the magnification of the image by X amount
Teleconverter have glass in them and like a the Sigma 1.4x and 2x and specificaly designed to be used with Sigma APO lenses, and will increase the shooting distance by X amount. eg. A Sigma APO 70-200 with a 2x TC will shoot 140-400. these TC's also have all connectors to allow the lens to run in full auto. they go between the lens and the camera (both)

[KevinR]

Interesting idea. I thought I had all the ingredients to bake the cake, but unfortunately my standard extention tubes don't fit over the extension piece of the 1.4xL rear convertor. So to test, you would have to look for tubes with a larger bore, or be prepared to machine one out.

Optically, its going to seriously mess with the focus distance. Perhaps you could test it out with a simple plastic tube spacer first..

[RioRico]

Yes, the effects of adding a tube section would be close-focus, greater magnification, and some light loss. The TC will also eat some light and degrade IQ somewhat.

The idea *should* work, if as KevinR says the tubes fit over the TC protrusion. But at what cost? Macro tubes with A-type connectors aren't cheap. Tubes with M-type linkage may or may not clear the TC. Light loss from a short tube sections should be minimal, but more noticeable with longer sections. A de-glassed A-type TC would work but will definitely be long enough to eat some light.

[zapp]

The 1.4x-L & 2x-L rear converters were only made for some lenses because the front element of the converter sticks out beyond the mount. Can you add a length of extension tube to the front of the converter to take up the space around the protruding front element and then attach it to your lens to make it fit with the lens you want to use it with?
As I understand it whatever length of extension tubes you use will decrease the minimum focusing distance as well as prevent you from focusing to infinity. Will the extension tubes have any other effect?

What are you trying to do?
A 2x TC will double your focal length, but keep the closest focus distance the same - in effect you increase the maximum possible maginfication by a factor of 2 as well - so even with a TC you can increase image scale.
Adding extra extension will result in an increased image distance. You wil not be able to focus to infinity anymore and that probably means you can only focus from very close to 1 or 2 m with a tele lens. Extra extension is not useful.
Read the instructions for converters - what lens are they made for. They wil fit nicely with these lenses, In case they cause trouble get a different TC - general brand TCs will typically have no protruding elements.

[Stone G.]

The 1.4x-L & 2x-L rear converters were only made for some lenses because the front element of the converter sticks out beyond the mount. Can you add a length of extension tube to the front of the converter to take up the space around the protruding front element and then attach it to your lens to make it fit with the lens you want to use it with?
As I understand it whatever length of extension tubes you use will decrease the minimum focusing distance as well as prevent you from focusing to infinity. Will the extension tubes have any other effect?

I use this kind of combination regularly for macro photography, specifically:

Tamron SP 35-80mm + 31mm extension + Tamron 2X TC

This works fine for macro, providing me with magnification ratios around 2:1 while maintaining a comfortable working distance.

- but what is your intended application?

[Lowell Goudge]

While inserting a tube in front of the TC may work, it is not ow they were intended to be used. These TCs were made for specific lenses and the optical design is somewhat "tuned" to those lenses. It may have some undesirable effects on image quality.

[littledrawe]

Thanks for looking at this folks. I don't have an intended use or purpose I was just thinking how to get the most use out of these products and on the off chance I can find the 1.4x-L for a reasonable price it may be more of a justification to buy it I was also wondering if anyone has tried these with these specific converters. I also understand there are problems fitting some of the sigma TCs to lenses because of their protrusions but I don't have one and have never had the problem so I was just thinking about it and thought this may be a way around it especially where some people say that some of these TCs and lens are close to fitting but not quite.

[Lowell Goudge]

i would think if you are looking for a good quality and general purpose TC the SMC-F 1.7x AF TC is the one to go for

[panoguy]

i would think if you are looking for a good quality and general purpose TC the SMC-F 1.7x AF TC is the one to go for

I would second Lowell's guidance here. Even the recent high prices of the 1.7x AFA are still going to be about equal to a good 1.4x-L, and the AFA adds the ability to be used with nearly any KA-mount lens adding autofocus. Optically, I can't say which is better, but I think the Pentax TCs (as opposed to the AFA) are made in such a way to "mate" with particular lenses as a replacement rear-element group (keeping and/or correcting the optical characteristics of the main lens) which is why they perform so well on those lenses.

[littledrawe]

i would think if you are looking for a good quality and general purpose TC the SMC-F 1.7x AF TC is the one to go for

and the AFA adds the ability to be used with nearly any KA-mount lens adding autofocus

I had the 1.7X AFA adapter and used it with great success on my tamron adaptall 2 300mm f2.8 lens. I took full advantage of the autofocus feature there. I sold the tamron and have not found a lens that the 1.7X works with as well yet. I didn't really like using it in manual focus and it didn't work well with the 400mm f4 lens I have now so I sold the 1.7X AFA adapter also since our relationship became a little strained. Like all TCs I suspect they work better with some lenses then others.
I think a fantastic idea would have been for the Pentax folks to have made a version of the AFA that didn't have the 1.7X magnification in it to truely transform all older k mount lenses into autofocus counterparts with much less magnification (say 1.2X magnification) and the ability to use it on lenses with smaller physical max apertures since the 1.7X autofocus is only reliable to f4.
My plan is this year is to get the A* 600mm and the 1.4x-L and I was just curious if I end up with the 1.4x before the 600mm can I use it the way I mentioned originally on cheaper lenses that it would not fit on without the extension tube spacer (if in fact that even works at all).