Manglesphoto wrote:
I would check to see if Pentax makes a set of tubes first, I have tried Kenko tubes but found the very aggravating due to the lose of the electrical connection on my Nikons, I ended up buying a set of Nikon tubes, at about twice the price and manual focus only which is not a problem for me since I shoot 99.9% in manual mode. At one time Pentax did have a bellows for the "k" mount cameras and lens.
That's interesting...
Nikon brand PK-11A, PK-12 and PK-27.5 tubes for the F-mount DSLRs all lack any electronic electronic contacts. They mechanically support AI (auto indexing) and "screw drive" autofocus with "AF" lenses... but provide no autofocus with AF-S or AF-P lenses, which are now much more common than AF. Without any electronic connectivity, Nikon branded extension tubes also will not support VR on lenses that have it.
In comparison, Kenko tubes have electronic contacts, in addition to mechanical connectivity. As such, they'll provide AF with all types of modern on all cameras that support it. (Note: D7000-series and higher support both "screw drive" and in-lens focus motors such as AF-S. AF-P is supported by the extension tubes, too, though that type of lens' functionality will be limited to recent camera models that fully support it.) VR is supported with all lenses than have it, too.
You must have a faulty Kenko tubes, for them not to work properly with Nikon cameras and lenses.
I've got a set of Kenko for use on my Canon, as well as several Canon brand tubes. The quality is top notch and both it and their function are virtually identical. They all work flawlessly. The only differences I see are that the Canon tubes have more refined internal light dampening and some slight external cosmetic differences. Someone told me that the Kenko use a plastic tube, rather than the magnesium used in the Canon. That doesn't seem the case with the older Kenko set I use. But maybe they've changed them more recently (I know that Kenko changed the mount to be compatible with both EF and EF-S mount Canon lenses. My older set only works with EF lenses.) The Kenko set of three (12mm, 20mm and 36mm) costs less than one 25mm Canon extension tube and only a little more than a single 12mm Canon tube. (Canon tubes are only sold individually and they don't offer any longer than 25mm.)
The original poster asked about extension tubes for Pentax, anyway. All the above may be a moot point, because the only tubes I can find for modern Pentax DSLRs is a Dot Line set of three (12mm, 20mm & 36mm:
https://www.bhphotovideo.com/c/product/896117-REG/Dot_Line_dl_mex_pk_Man_Ext_Tube_Set.html)... There don't appear to be any Pentax brand tubes available. The Dot Line set is cheap ($20), but it has no electronic or mechanical connectivity. They're what I call "dumb" tubes, which are purely manual... both manual focus AND manual aperture. With this type of tube, the lens MUST have a mechanical, aperture control ring on it, to be able to stop it down... Most modern Pentax K-mount lenses have an electronically controlled aperture that will only be usable wide open on these tubes (making for extremely shallow depth of field at close distances). There are a few Pentax and third party lenses still offered with mechanical aperture control ring. Many vintage Pentax lenses have that ring and would be usable, but of course will be manual aperture and manual focus only.
EDIT: Searching a little farther online, I found a set of Movo extension tubes (two: 20mm and 36mm) in Pentax K-mount that appear to fully support modern, electronically controlled lenses. Those would allow full aperture control, maintain wide open aperture during focusing and automatically stop it down during exposure, and allow auto focus to work. They seem a fair value at $99.
https://www.newegg.com/p/0UF-00FA-00167?Item=9SIA5ST9283010&source=region&nm_mc=KNC-GoogleMKP-PC&cm_mmc=KNC-GoogleMKP-PC-_-pla-Movo%20Photo-_-Accessories%20-%20Camera%20Other-_-9SIA5ST9283010&gclid=Cj0KCQjww47nBRDlARIsAEJ34bmfTvpf3wJ5zDD9AqDSIk9FNQbUWmR5JFlh3TSJX4ex_PdkaCLvwwYaAgReEALw_wcB&gclsrc=aw.dsIf you want to be able to use modern electronically controlled Pentax lenses, definitely buy this latter set... not the cheap Dot line "dumb tubes".
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