Pentax 67 extension tubes

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Robert Feinman - 29 Jul 2007 18:17 GMT

Would someone please explain how the extension tubes for the Pentax 67
work?
Do they allow for automatic diaphragm stopping down for example or is it
necessary to set the lens to manual mode?
So far I've only used close up lenses for the occasional "macro" shot,
but this suffers from the usual sharpness problems.

Thanks..

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Robert D Feinman - Landscapes, Panoramas, Photo Tips
Web Site: http://robertdfeinman.com

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David J. Littleboy - 29 Jul 2007 18:56 GMT

> Would someone please explain how the extension tubes for the Pentax 67
> work?
> Do they allow for automatic diaphragm stopping down for example or is it
> necessary to set the lens to manual mode?
> So far I've only used close up lenses for the occasional "macro" shot,
> but this suffers from the usual sharpness problems.

At least on all my Mamiya 645 lenses, closeup lenses work superbly. As they
do on my 5D.

I suspect you are having mirror slap or other problems. (Or are you doing
stamps, paper money or other things that require a flat field and no
distortion?)

Extension tubes aren't optimal either, since most lenses aren't optimized
for closeup work. (There's an article on Bob M's MF site that finds closeup
lenses better than extension tubes some of the time.)

David J. Littleboy
Tokyo, Japan

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Duncan - 30 Jul 2007 07:13 GMT

I agree that a micro/macro lens is far superior since they were designed for
this in mind. I use tubes manly to reduce the minimum focusing distance
rather than fro what they were touted for as macro work.

What I have used successfully are enlarging lenses, manually on bellows with
appropriate mount adaptors as a work around. But either way the macro lenses
are not cheap and the adaptors aren't either. I have them as my systems have
built up over the years and so a simple matter for me to choose what I need
from the kit available.

So in your case you need to justify the cost over results and or if relevant
the return from a job/commission that you are shooting for.

Duncan

>> Would someone please explain how the extension tubes for the Pentax 67
>> work?
[quoted text clipped - 16 lines]
> David J. Littleboy
> Tokyo, Japan

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Randy Stewart - 29 Jul 2007 19:33 GMT

> Would someone please explain how the extension tubes for the Pentax 67
> work?
[quoted text clipped - 4 lines]
>
> Thanks..

The Pentax extension tubes, used a single units or in combination, mount to
the inner bayonet mount of the body and do couple the automatic diaphram.

To clarify the possible confusion in an earlier reply, I assume that by
"close up lens", you are mean a close-up diopter lens mounted like a filter
to the front of a standard lens, not a true macro lens such as the 135mm
marco lens for this system. Pentax does/did make a couple of two element
diopter lenses of that type, but they must be matched to a specific group of
regular lenses and used at reduced aperatures, or image quality will suffer.

Randall Stewart

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Lake - 01 Aug 2007 23:12 GMT

> The Pentax extension tubes, used a single units or in combination, mount to
> the inner bayonet mount of the body and do couple the automatic diaphram.

<snip>

Pentax also has a set of outer-mount extension rings for those lenses
(400mm and up, with exceptions) that mount to the outer bayonet mount
of the camera. They require manual aperature operation.

Pentax also makes an (inner mount) helical extension ring that gives
you variable magnification within the range of the tube.

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