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01-22-2012, 10:10 AM - 2 Likes   #1
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My new(old) SDM Extension Tube conversion

With advice and inspiration from RioRico (thank you), I purchased a ProMaster Spectrum 1.7x teleconverter on ebay for conversion to an extension tube. This teleconverter looks remarkably like the Tamron 1.4x teleconverter, but costs less than 1/2 as much (roughly $100 on ebay).

I wanted to use the extension tube with my sdm lenses. which have no aperture ring. After purchasing, i tried the 1.7x teleconverter with my DA50-135 and the screwdrive DA35 macro. It worked with both those lenses, however, indoors, in low light, the DA50-135 would hunt without locking. I also have a 1.4x Tamron teleconverter which focuses in a much more positive fashion, so decided to convert the ProMaster instead.

The tools required to do the conversion was a #000 Philips head screwdriver, available from Sears for $2.95, and a LensWrench for the locking ring that holds the lens in place in the center of the teleconverter. There are available on ebay for $40 to $60. Get the multiple tips models that allow the most flexibility.



After installation of the new Extension Tube behind the DA*50-135, the maximum focus distance has decreased from infinity to about 40 inches max. The thickness of this Extension Tube is 11/16" (17mm). The SDM capability of the lens has been preserved and works effortlessly. One does have to refocus after each zoom as RioRico has said, there is a narrow area of focus for each zoom FL. Its easy to get the hang of, though.



The small Extension tube is lightweight and small to carry. It allows my 50-135 to close-focus and act as more than one type of lens. I'll try it with my DA-300 today and attach more pics of that.




01-22-2012, 10:20 AM   #2
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Thanks for taking the time to post this, sounds like a great idea. Can you add the exact model of the tele-converter if there is one?
01-22-2012, 10:51 AM   #3
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QuoteOriginally posted by jatrax Quote
Thanks for taking the time to post this, sounds like a great idea. Can you add the exact model of the tele-converter if there is one?
Thank you!!! I've given all the model information in the picture and text except that it doesn have on the side:

Promaster Spectrum 1.7x
Teleconverter for Pentax Z AF

- you can look at the reviews of them in the Lens Section database on this PF under the Misc. Lenses or some such heading for the teleconverters. There are other Tamron like models out there as well. If you want to do sdm lens, try to make sure that the sdm runs all the way thru the lens, apparently there are some converters that have the sdm contacts on one side, but not the other (???).

If one wants more magnification, then there are tons of 2x teleconverters out there and are cheaper, the smaller ones like this one are harder to find and more costly. thanks!
01-22-2012, 01:07 PM   #4
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Good job! Yes, a lens wrench is the right tool for diddling with glass. And yes, the multi-tip version is worth the extra money. Not all slots are created equal. A lens wrench lacking the right tips is rather useless.

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