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PostPosted: Wed Jan 21, 2009 9:22 am
by lightrae
I'm looking for an adjustable extension tube with Canon EOS mounts. Full function would be perfect, AF would be good and manual operation is ok.
I am NOT interested in any fixed-length tubes nor stacking tubes.I have a beautiful Pentex helicoidal adjustable tube with K mounts but I can't find any other manufacturer for any other type of mount. I'm even considering cannibalizing a set of Canon mounts and swapping them with the K mounts.
I would be thankful to hear if anyone has encountered such an adjustable tube. Even vague recollections could be helpful.

Ralph Eldridge


PostPosted: Wed Jan 21, 2009 2:13 pm
by dang
Sounds like you're wanting an auto macro bellows system?
Check Navoflex: ... Canon.html


PostPosted: Wed Jan 21, 2009 2:47 pm
by lightrae
Thanks, Dang, but that's not what I can use (too bad though).

First; I would require an extension tube to mount my Canon 5D body.
Second; I want to mount my 300mm, f2.8L IS both with and without a 2X II converter.
Third; This is for hand-held and monopod/gimbel field shooting of wildlife. I don't want the dirt and bother of constant changes and the fewer connections the better.

I have tried PK/EOS adapters but their design and/or fit is poor. I'm unwilling to risk damage to either my body or lenses by using them. If I have to use my PK unit I will put on EOS mounts. I'm just hoping that someone has run across something that I can use instead of my pentex unit.

Your suggestion, Dang, is the best and nearest that I've received so far.

My main goal is to reduce my focus distance over a linear range. That's why I like the Pentex so much. It acts exactly like a twist adjusted zoom lens.


PostPosted: Wed Jan 21, 2009 6:20 pm
by dang
You're welcome, sorry it's not what you're after.

If you don't mind my asking, what type wild life shots are you after? I'm assuming you want more focus distance, with greater magnification than can be achieved with a standard macro lens? But what size subject are you trying to photograph? Whats confusing me is if you add lens-less extension of any type, you'll lose infinity focusing. Thus, if you're shooting birds wouldn't you still need to remove it (extension) at times? Maybe I'm missing your point, unless you're needing some type of variable teleconverter.


PostPosted: Wed Jan 21, 2009 9:09 pm
by lightrae
Sorry, Dang, I should have described my "why" more fully. I just want to shorten the focus distance of my long lens.
I shoot wildlife, especially birds, as much as possible with my 300mm, f2.8L IS lens on a 5D body. When light permits I throw in a 2X II doubler. And very often I find myself too close to focus.
Changing lenses is no help but an extension works well. Also, I want minimum lens changes to lower the risk of dirt penetration.
I inserted my Pentex helicoil extension with PK/EOS adapters and it worked ok. I just don't like the weak, jury-rigged set-up, what with all the weight and stress that this rig has.
I have these suggestions from another forum that may produce results:
The Zork from
Vivitar Macro Focusing Teleconverter
Possible adaptable equip0ment in medium format.

I figure a single metal tube would mount on the 300mm with no more stress than the 2X converter.


PostPosted: Thu Jan 22, 2009 12:52 am
by dang
Okay, I see...
While the Zoerk is a fine system, it's not close to what you're after. The Vivitar isn't quality enough to consider mounting before an L lens, and I'm not familiar with any medium format equipment thats going to be helpful in such a situation.

Now, for the original thoughts of a bellows... one will be even more restrictive than a lens-less extenision, here's why:
1. They only compress so much, so it wouldn't offer any advantage over an extension tube.
2. It's going to be more flimsy, and can't support the 5.6 lbs of your 300mm as well as a tube.
3. Actually, bellows I've used are generally thicker at full compression than a #3 tube, so would be more limiting in long focus because of it.

What you're really needing is a reasonably sharp lens, with close focus ability. As an alternative to an auto bellows, you might consider an old 100-300 f/5.6L which has "close focusing". Information can be found in the on-line Canon Camera Museum: ... index.html

Of course, the easiest option is to change lenses, and not be too concerned with dust. Just purchase some pads to clean your sensor after each outing instead.

I know that isn't what you want to hear, and I understand 8.2 feet minimum focus is restricting. Mark it up as the price for having the sharpest lens you can get, and it's limitations are required for it's strength.

If you find something which does what you're wanting, I'd love to hear about it.

Thanks, you've got me thinking. Just wish I had a better suggestion.


PostPosted: Thu Jan 22, 2009 4:13 am
by lightrae
Thanks for the very succinct assessment, Dang.
I'm inclined to agree with you.
I bought the 300mm for speed. The f4 and f5.6 lenses just weren't cutting it. I've never regretted the decision. I'm just investigating options.

On the down side, I got the 8 foot focus @ 300mm. :(
On the plus side, I got a 600mm with a 8 foot focus instead of the near 20 feet of some 500mm and 600mm. :D
Everything with light is a trade-off. I made informed choices and, mostly, it's working for me but there's always that wish list, that perfect lens. :lol:

Thanks again.


PostPosted: Thu Jan 22, 2009 10:41 am
by dang
Thank you, Ralf...
I enjoyed the discussion, and you got me into your galleries again (which was long overdue). You've some really nice work.

Yes, it would be great to find the "Perfect" lens... too bad there's not one. Of course, then we wouldn't have an excuse to buy more than one! :D


PostPosted: Thu Jan 22, 2009 2:10 pm
by lightrae
I always enjoy exchanges, Dang. The info gleaned always seens to prove useful sooner or later and send me along routes that I likely would have missed on my own.
This has been a prime example. I think that I've found what I want. I'm just awaiting additional info. ... 14063.html


PostPosted: Thu Jan 22, 2009 5:23 pm
by dang
Interesting, from a manual macro standpoint, but macro uses shorter lenses.

36mm minimum is going to keep your focus distance from infinity "in" quiet a lot, and it appears to be made from plastic (though I might be wrong)? You'll also lose all auto functions, including focus.

Personally, I'd think a set of auto tubes might be a better consideration. When using manual aperture/focus, the viewfinder can get pretty dark, and you'll likely not want to shoot wide open.


PostPosted: Thu Jan 22, 2009 7:31 pm
by lightrae
I'm also concerned with strength and functionality and I'm hoping that unit comes in matte finished metal, not plastic.
However, this is the way that I want to experiment. I'll collect more info and then decide about actually obtaining one.
Of special note in that review was reference to several similiar units from several manufacturers. I take that reference to indicate that there are other adjustable tubes out there waiting to be found. That's been my problem until now: just finding if they existed. Now I have a solid starting point I can investigate and decide if the trade-offs are acceptable.
Maybe, perhaps likely, I'll find at some point that things aren't turning out the way I hope but I'll have satisfied my curiousity. :lol: