[csa]

I'm interested in getting a set of extension tubes to use with my K3 and Sigma 105 Macro. Any suggestions as to what to get, and any information using them would be appreciated!

[pathdoc]

First and most important question: does your lens have an aperture ring?

If it does, anything goes.

If it doesn't, you'll need something with at least A contacts if you're not going to spend your life at f/22 (or whatever the narrowest aperture is, probably f/32 at that focal length). Actual T/C with A contacts are rare, although someone else was asking about them and third-party ones do exist. Otherwise a deglassed P-K A or P-K AF teleconverter will do nicely, even a third-party one, because you're going to be ripping out the glass anyway.

[Stone G.]

How much more magnification are you aiming at? You will need some fairly long tubes to get a substantial extra reach with a 105mm lens. Besides, extension tubes with electric contacts are rare and expensive. If your lens has an aperture ring, you might consider to work fully manual.

With my Pentax DFA 100mm macro I get fair results with the Pentax A-2SX and the HD DA 1.4 teleconverters, which also let me keep a comfortable working distance.

[csa]

First and most important question: does your lens have an aperture ring?

Yes, it does.

"because you're going to be ripping out the glass anyway."

I really am not comfortable going this route, simply want something ready to use.

[csa]

With my Pentax DFA 100mm macro I get fair results with the Pentax A-2SX and the HD DA 1.4 teleconverters, which also let me keep a comfortable working distance

Ahh, I have a 1.4 TC, never thought of using that!

[pentageek]

As far as I remember Sigma 105 macro has got aperture ring, so as pathdoc said, 'anything goes'. Just my 2 cents: even simple rings should have metal (or at least conductive) surface of the mount. The rationale is pretty simple - this way we can convince the camera to work as with 'A' lenses. I have rings with plastic mount, and it makes the camera detect the ring as 'M' lens, what is definitely less convenient.

[pathdoc]

Yes, it does.

"because you're going to be ripping out the glass anyway."

I really am not comfortable going this route, simply want something ready to use.

In that case your options range from the semi-expensive (there are Pk teleconverter tubes out there, third party, for about $100 US) to the absurdly cheap ("dumb" tubes that give you stop-down metering only, $7.00 on e-bay!!), and Pentax K helicoids or aperture-coupled (green button metering) genuine tube sets which drift around somewhere in between and occasionally slightly higher than $100, but the smallest of which offer you options which don't require you to ram your macro lens two thirds up a bug's nostril.

Remember that the more extension you put on, the closer you CAN get but also the closer you HAVE to get. And while a 100-ish millimetre lens with an inch of extension tube isn't quite as bad as, say, a 28 (which DOES have to be practically right up a bug's nostril before it will focus), there may be times (depending on the liveliness and potential hostility of what you are photographing) that you want to back off with alacrity.

[csa]

Thanks guys, great advice!

[baro-nite]

Another way to approach this is to start with the magnification range you're trying to achieve. Then consider which option makes the most sense: tubes, bellows, supplementary lens. What size subjects are you thinking of?

[csa]

Mainly insects would be my targets.

[stevebrot]

One caution in the land of "anything goes"...On the counter behind me is a very pretty Soligor K-mount Auto extension tube set (supports automatic aperture actuation and open aperture metering with non-crippled mount bodies). Sadly, the "male" side of each tube in the set is made of anodized aluminum and does not conduct electricity. As a result, the aperture on the host lens will not close for exposure when used with your K-3, nor will the lens stop down for metering.*

The workaround is to sand down the anodizing to bare metal on the portion opposite the "data pin" on the camera mount face.


Steve

* Ironically, it will work without modification on the K10D on your signature.

[csa]

Steve, that's sure weird that it would work on the K10, but not the K3, isn't it?

[pathdoc]

The workaround is to sand down the anodizing to bare metal on the portion opposite the "data pin" on the camera mount face.


Steve

* Ironically, it will work without modification on the K10D on your signature.

That or thin electricians' conducting tape.

[baro-nite]

Mainly insects would be my targets.

OK, then working distance is a priority and you probably want to work hand-held, so tubes are a good choice. As pointed out above, even a full set of tubes doesn't get you a huge magnification increase with a 105mm lens, but even the difference from 1x to 1.5x or so is substantial.

I have various extension tubes: a set of Pentax fully-manual tubes, a couple of Pentax helicoid tubes (also fully manual), and various old 2x teleconverters from which I've removed the glass to get A-type tubes. (See here for an example of a 2x TC with easily-removable lens elements.) I expect that some of the cheaper eBay stuff is fine too, but YMMV. As noted above, anodized surfaces are an issue; I've had mixed results with sanding them down so personally I have stuck to the non-anodized ones.

[csa]

easily-removable lens elements

What is the process to remove lens element?