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03-09-2012, 09:24 AM   #1
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Extension tubes, M42 lenses, mounting

Is there any difference between mounting a M42 lens onto M42 extension tubes and then an adapter to the camera body, vs. mounting the M42 lens via the adapter onto K mount extension tubes? If there isn't a difference, then it would seem having one set of K tubes should be sufficient rather than needing both M42 and K mount tubes?

03-09-2012, 09:31 AM   #2
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HA! I just posted your question and my long answer in another thread about 30 seconds after you started this thread! Right here: https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/178345-macro-tubes-question.html
03-09-2012, 09:35 AM   #3
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Or if you prefer, here is my answer:

Well, there is *mostly" no difference between mounting a screwmount lens onto screwmount extension which is mounted via adapter to the camera, and mounting the lens on an adapter onto PK tubes mounted on the camera. Like this:

lens -- M42 extension -- adapter -- camera
vs
lens -- adapter -- PK extension -- camera

So you'd think that one adapter and one set of tubes would be enough. But life is more complex. Some factors:

1) For longer lenses, just one set of tubes, even with bellows attached, won't be long enough to achieve much magnification. I need bellows plus several tube sets for close usage of 160-190mm enlarger lenses. Luckily, tubes are very cheap.

2) Various cheap M42 tubes from different sources, and the standard cheap PK tubes, may be of different thicknesses. I often use thin tubes to rather finely adjust the focus ranges of some lenses, and sometimes 1mm can make a difference.

3) Not all M42 tubes have the same depth of threading. This means I can put a mid-range enlarger lens on a deep-thread tube and have some focusing ability, rather than be stuck with a fixed-focus. Thus I keep several different sets of M42 tubes.

I also have several sets of standard cheap PK tubes. These are useful for more than just macro work. I may glue a tube and mount to a wide projector or copy lens body, using those as a cheap PK adapter, to be mounted on PK bellows. That's how I manage to use some exotic (and cheap!) Schneider and Rodenstock and Extar lenses. Other lenses with odd or no mount threads can be adapted by drilling a hole in a cheap thick black PK or M42 body cap, then inserting the lens, and mounting it on extension. But sometimes gluing a tube to the lens body is the only trick that works.

I find that some lenses need my heavier PK bellows and tubes, and some are just fine with the lighter-weight M42 extension; and some REQUIRE one system or the other to get the right fit. If you just want to put an M42 lens on extension for general close work, then the answer to your question is, "No difference". If you want to use a wide range of lenses in curious ways, then it's good to have more gear.
03-09-2012, 09:54 AM   #4
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If you'll only have one set, PK tubes will be most convenient. You'll need an m42 lens - PK body adapter in either case.

Finding a PK lens to m42 body adapter is very difficult

03-09-2012, 09:58 AM   #5
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QuoteOriginally posted by newarts Quote
Finding a PK lens to m42 body adapter is very difficult
So is exceeding the speed of light.
03-09-2012, 10:19 AM   #6
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Just want to second that there's not much practical difference between the two methods. I've done both, and either way works fine. I usually use the m42 adapter in PK tubes though, as they happen to be a better set of tubes.

One potential gotcha with really cheap tubes (of either type) is that they can droop if not well made. I've seen some so flimsy that I wouldn't want to trust them with a lens that is the least bit valuable. Good quality tubes are a good investment.
03-09-2012, 11:04 AM   #7
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QuoteOriginally posted by Philoslothical Quote
Just want to second that there's not much practical difference between the two methods. I've done both, and either way works fine. I usually use the m42 adapter in PK tubes though, as they happen to be a better set of tubes.

One potential gotcha with really cheap tubes (of either type) is that they can droop if not well made. I've seen some so flimsy that I wouldn't want to trust them with a lens that is the least bit valuable. Good quality tubes are a good investment.
Wow! Tubes are so easy to make I'd think that'd be rare.

I've a few sets of very cheap pk & m42 tubes and haven't seen a problem. All my tubes are metal & I suppose plastic tubes might be riskier?
03-09-2012, 11:19 AM   #8
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Yeah it's the plastic ones I'm talking about. You can find them on Amazon or Ebay for a few bucks, but they're not worth buying imo. Metal is the way to go. I have a set of AT-22 tubes with the aperture linkage, and love them. Definitely worth picking up if you can find them, just for the convenience metering. I'll eventually spring for another set, but right now if I need more magnification I just do reversed lens stacking.

03-09-2012, 01:01 PM   #9
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QuoteOriginally posted by Philoslothical Quote
Yeah it's the plastic ones I'm talking about. You can find them on Amazon or Ebay for a few bucks, but they're not worth buying imo. Metal is the way to go. I have a set of AT-22 tubes with the aperture linkage, and love them. Definitely worth picking up if you can find them, just for the convenience metering. I'll eventually spring for another set, but right now if I need more magnification I just do reversed lens stacking.
I've not run across plastic tubes; the cheap ones I get on eBay for about US$6 shipped from China are all metal. I've had zero problems with any of them, except maybe not having enough! The cheaper non-auto M42s and the older types with auto-stopdown linkage are each useful in different ways, as their internal clearances may vary.

The most inexpensive way I know for A-type support (auto stopdown and metering) is by deglassing old A-type TCs. The 2x TCs I've modded (using a lens spanner to remove the internal glass elements) are each about 25mm thick, so they take my FA50/1.4 to 1:1. (I haven't bothered chopping my M-type TCs.) Downside is that the finer increments of the usual 10+15+25mm sets aren't available, just 25mm increments.

As usual, I'll point to my canonical article: https://www.pentaxforums.com/forums/pentax-lens-articles/152336-cheap-macro-b...lose-work.html
____________________________________

In case anyone is interested: For my current long journey, I left my PK bellows and tubes and TCs back at the homestead. For close work now, I have:

* a Macro-Takumar 50/4 (1x)
* a set of +1+2+4 closeup optics
* a Raynox DCR-250 closeup optic
* a Schneider Betavaron enlarger zoom
* enlarger lenses (50-75-90-110-127mm)

* a few PK mount-reversal adapters
* various screwmount-PK adapters
* a little Bellowscope M42 bellows
* M42 17-35mm focusing helicoid
* about 120mm M42 macro tubes

That should be enough to keep me busy. Now I need to crawl around in the vast desert for suitable subjects. Or maybe in the mine tailings.
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