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02-27-2016, 01:03 PM   #16
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QuoteOriginally posted by WPRESTO Quote
Only using one of the discontinued K-mount Pentax bellows. As noted above, these have a diaphragm operating mechanism in the front standard that is operated using a mechanical cable release. Press the cable release to close the diaphragm.
For a lens with no aperture ring won't this just give you the option between wide open and completely stopped down? Or can you choose in-between settings?

I was thinking with all those adapters from k-mount to the various mirrorless systems available with built in aperture control rings (ex. https://www.pentaxforums.com/forums/136-pentax-q/233319-new-fotodiox-k-q-adapter.html) these may be a reasonable way to put DA lenses onto tubes (with another adapter), or use reversed, and still have some aperture control.

02-27-2016, 01:19 PM   #17
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QuoteOriginally posted by BrianR Quote
For a lens with no aperture ring won't this just give you the option between wide open and completely stopped down? Or can you choose in-between settings?

I was thinking with all those adapters from k-mount to the various mirrorless systems available with built in aperture control rings (ex. https://www.pentaxforums.com/forums/136-pentax-q/233319-new-fotodiox-k-q-adapter.html) these may be a reasonable way to put DA lenses onto tubes (with another adapter), or use reversed, and still have some aperture control.
Correct. You would have to "guestimate" the amount the aperture was closed down,

I'm not sure that the mirrorless adapters have an indication of the aperture being used. To use such an adapter as an extension tube for a Pentax lens on a Pentax camera you'd need an additional tube with a female mirrorless mount at one end and a male Pentax K-mount at the other. Not sure there is such a thing.
02-27-2016, 01:25 PM   #18
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QuoteOriginally posted by WPRESTO Quote
Additional images from my tests of macro options.

1) a 200mm SMCA mounted on a Pentax bellows that has a diaphragm operating mechanism (notice the mechanical cable release threaded into the front standard). Fully extended as shown, this rig provides approximately the same magnification as the 70mm f2.4 with a 2.5X Raynox attached;
2) penny photographed with the preceding rig - compare to the image posted earlier of a penny taken with a 70mm f2.4 + Raynox 2.5X;
3) crop from preceding image file; the IQ with this rig is very good.
4) on left a set of K-mount Keno extension tubes that have diaphragm operating linkage and aperture information transfer contacts; on right a Kenko Uniplus Tube, 25mm length, that has aperture information contacts, diaphragm operating linkage, and AF connection. SFAIK Kenko no longer offer either of these in K-mount.
Impressive results... and, I have to say it - a great looking rig (I know, I know... it's what it does that counts, but that setup does look great!)
02-27-2016, 01:38 PM   #19
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Bellows do look nice, appealing to the gadget-head that lurks in so many of us (not all). However, bellows are strictly for studio work and primarily static subjects, not for live insects in the field.

Below is the way I usually use bellows, with a 4X Plan APO Nikon microscope objective. (this bellows is M42 mount, for which it's much easier to get an RMS adapter)
AND ALSO, a more solid way to mount a microscope objective using T-tubes, here shown with a 20mm Zeiss Luminar.

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02-27-2016, 01:41 PM   #20
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I took an old KENKO KAX 2x teleconverter, and removed it's lenses to make my extension tube. I think I paid $5 for it.

This allows the camera to still control the aperture on my DFA 100.

But that only gets you a little closer.
02-27-2016, 01:43 PM   #21
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QuoteOriginally posted by WPRESTO Quote
I'm not sure that the mirrorless adapters have an indication of the aperture being used. To use such an adapter as an extension tube for a Pentax lens on a Pentax camera you'd need an additional tube with a female mirrorless mount at one end and a male Pentax K-mount at the other. Not sure there is such a thing.
I think some have vague click stops, so you could at least be consistent from shot to shot. But yea, I haven't been able to come up with a combo of adapters that would work for tubes/bellows, there is a lack of mirroless mount to k-mount adapters. I'm guessing the flange distance and loss of infinity focus would be the reason, but it wouldn't matter for use on tubes/bellows.



Also thanks for posting these examples!
02-27-2016, 01:56 PM   #22
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QuoteOriginally posted by Riggomatic Quote
I took an old KENKO KAX 2x teleconverter, and removed it's lenses to make my extension tube. I think I paid $5 for it.

This allows the camera to still control the aperture on my DFA 100.

But that only gets you a little closer.
The general formula or calculation for the magnification achieved by extension tubes or bellows WITH THE LENS SET TO INFINITY is

extension tube or bellows length divided by focal length of lens = magnification.

SO, to get 2X life size with a 100mm macro that focuses to life size, you'd need to focus the lens at its closest distance and add about 100mm of extension. The bellows extension behind the 200mm SMCA pictured above is insufficient to get to life size even with the lens set to its closest focus position. It's easy to see why for higher magnifications it's better to use a short focal length lens, or reverse mount the lens (=less extension needed) or use something like a Raynox.

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