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06-18-2011, 10:12 AM   #1
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Looking for specific type of lens, plz help

Hello,

Quick q. For you lens experts out there - I'm trying to identify a cheap and nasty lens to purchase in order to take the glass out and use it for a pet project of mine. Specifically, any k mount lens which is about 5-10 cm long, but extends to 15 to 20 cm. I'm looking at a macro I think - any suggestions?

Thanks!


Last edited by Nass; 06-18-2011 at 11:37 AM.
06-18-2011, 10:44 AM   #2
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I think you'll have a hard time finding what you want. The old macro-takumar 50:4 1:1 lens has a double helicod with a lot of extension - 50mm total.

Any non-IF 1:1 macro lens will have an extension equal to its focal length.

Good luck finding one. Can you use a Bellows?

Last edited by newarts; 06-18-2011 at 11:46 AM.
06-18-2011, 11:36 AM   #3
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Thanks newarts - yes, it's actually to replace a bellows - I'm making it into a variable length extension tube. I've got an m50 macro which will do what I want but I don't really want to destroy it, was hoping for some cheap and cheerful alternative =)
06-18-2011, 11:43 AM   #4
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QuoteOriginally posted by Nass Quote
Thanks newarts - yes, it's actually to replace a bellows - I'm making it into a variable length extension tube. I've got an m50 macro which will do what I want but I don't really want to destroy it, was hoping for some cheap and cheerful alternative =)
Helicoid extension tubes were made & if you are lucky you might find a few. If you are even luckier you might be able to afford them.

Die Cast Pro - Asahi Pentax Helicoid Extension Tube
http://shop.ebay.com/i.html?_from=R40&_trksid=p5197.m570.l1313&_nkw=helicoid...All-Categories

Your best bet might be to place a "wanted" ad here for a junk 1:1 macro lens & use its helicoid.

06-18-2011, 11:46 AM   #5
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Isn't it easier to find a bellows?

foto-tip - photo accessories
06-18-2011, 11:51 AM   #6
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Those are neat =). You're right, that's probably the best route, scouring ebay's "lenses for parts" gets a bit boring. Ron, thanks but no I specifically don't want bellows.
06-18-2011, 11:52 AM   #7
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Amazing what Pentax used to make back in the day =)
06-18-2011, 11:59 AM   #8
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QuoteOriginally posted by Nass Quote
Amazing what Pentax used to make back in the day =)
It may be practical to inexpensively fabricate an adjustable nested-tube based rigid extension tube from appropriate cheap extension tube ends and nesting tubes. It wouldn't be pretty most likely.

1-3/4" ID and 1-3/4" OD tubes are standard machine shop items.


Last edited by newarts; 06-18-2011 at 12:06 PM.
06-18-2011, 12:26 PM   #9
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Some 35mm-slide projector lenses are built with loose large-helicoid tubes. I have a GoldE 5-inch f/3.5 Anastigmat whose tube is 5.5cm, extending to 10cm. I mount this on cheap PK macro tubes via a thick-flange M42-PK adapter. Glass/tube inner diameter is 3cm+. If I had a bad copy of this (but mine is good!) and knocked out the glass and used a full 5cm set of tubes, it would exactly meet your specs.

Thus: Look for old projector lenses. My costs: lens, US$2.25 shipped; M42-PK ring, US$3.50; PK tubes, US$7. Such a deal!
06-18-2011, 12:35 PM   #10
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QuoteOriginally posted by RioRico Quote
Some 35mm-slide projector lenses are built with loose large-helicoid tubes. I have a GoldE 5-inch f/3.5 Anastigmat whose tube is 5.5cm, extending to 10cm. I mount this on cheap PK macro tubes via a thick-flange M42-PK adapter. Glass/tube inner diameter is 3cm+. If I had a bad copy of this (but mine is good!) and knocked out the glass and used a full 5cm set of tubes, it would exactly meet your specs.

Thus: Look for old projector lenses. My costs: lens, US$2.25 shipped; M42-PK ring, US$3.50; PK tubes, US$7. Such a deal!
Good idea as usual from this poster!
06-18-2011, 12:35 PM   #11
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Epic - exactly the sort of things I'm after. Thanks gents =)
06-18-2011, 03:29 PM   #12
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there are some commercially available focusing helixes.\

I have one for my M42 set, whihc really acts lime a 15-30mm expandable extension tube.

there is also the vivitar macro-focusing 2x teleconverter, that has a 50mm extension capability built in so that it gives 1:1 with a normal - non macro 50mm lens
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