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12-23-2008, 09:01 AM   #1
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macro extension tube on ebay

I find this macro extension tube for M42 on ebay.


.Macro Extension Tube Ring for M42 42mm screw mount - eBay (item 330282021838 end time Dec-26-08 08:56:18 PST)

My takumar m42 screw in the tube nicely.
but the tube did not screw all the way in my spotmatic sp 1000.


The seller is keeping telling me I did a mistake in my order...
In is last reply He respond...the M42 do not fit the pentax body.

What a joke.

I get what I paid for.... A p.o.j...

marc

12-23-2008, 01:15 PM   #2
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I sympathise with you, Marc.

Although there is much good product that now comes out of China, there is also a lot of stuff that is poorly designed or made. Having had a little experience with manufacturing there, I know that there's more than one reason for this happening. That's little consolation for you, though.

My disappointing experience was with buying a M42 to K-mount adapter, which looked good in the eBay ad, but which failed dimensionally on three counts. It would actually go into the K-mount body, with a bit of jiggling, but was extremely reluctant to come out again, even with the supplied key!

To cap it off, the M42 thread was wrongly aligned, so the lens finished up at an awkward angle. Focus to infinity seemed to be OK, but of course the aperture and distance markings were about 120 degrees away from their usual place.

Measurement of the critical dimensions with a vernier caliper indicated that the adapter was a bit thicker than the Pentax original I bought when I got my first K-mount camera in 1981, and side-by-side comparison of the two showed that the bayonet lugs were quite different in arc-length and position relative to the alignment red-dot.

Quite how this can occur in the manufacturing centre of the world defeats me, except that I know there are small back-yarders operating there, with nothing but a lathe and some simple hand tools, and a lack of understanding of the things they make cheaply. Anyone with even an old copy lathe could have avoided some of the dimensional errors on this relatively simple piece of machining. In my case, I can fix the over-thick dimension fairly easily, but the other problems render the piece worthless.

It's a great pity things like our experiences occur. Some very basic engineering workshop techniques could have produced near-perfect results at the same price.

Rob
12-23-2008, 01:23 PM   #3
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most of the genuine pentax m42 extension tubes can be had pretty cheap. they are rather common. you do get what you pay for.
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