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12-18-2011, 10:49 PM   #1
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Super Takumar 50/F1.4 MF focussing accuracy test using LV

I've got a Super Takumar 50/F1.4. My copy won't focus sharply past 11m (this is with a recessed M42 adapter on a Pentax K-mount), so landscape usage is out, but there's a lot of stuff you can shoot within that distance.

This version has the white dot in the f/2 aperture ring position, so it's a late model. Some of the late models had the SMC surreptitiously applied, but I don't think this one does, so it's contrast is probably inferior to the SMC version. It would have been manufactured 1967-1970. Serial Number is 2458xxx.

The later SMC version definitely had the SMC coating, 8 aperture blades instead of 6 (you can seen a hexagonal shape in the bokeh of the shot below), and I believe that at least some of SMC versions (maybe all) had the mechanical aperture coupling lever.

This is a thoriated lens and I had to de-yellow it by exposing it to sunlight for a few weeks.
Interesting links to articles about mildly radioactive lenses are found here:

Radioactive lenses
Introduction of Thorium Oxide into Super Takumar Lenses
Radioactive lenses - Camerapedia
(the radio-active element is the last one so there's much more radioactivity from the rear of the lens than from the front.)
Radioactive Camera Lens From The 1960's

I've had problems getting a consistent focus as I don't have a split-prism focusing screen. Anyway I've tried 10x magnification in LV on the K-5 and it works well on a tripod with a static subject.

Here's a test of focus using LV. I focused on the small dark rectangular defect near the bottom of the orange flower. The top of the blue part may look like it's over-exposed, but the top of it is very pale. Perhaps it's sun-bleached. Pentax K-5, 1/640s, f/2.8, ISO80.

Here's a 100% (un-resized) crop so you can see the focusing accuracy:


Last edited by dosdan; 02-02-2012 at 05:40 AM.
12-18-2011, 11:15 PM   #2
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I also got one of those but haven't really tried it out since it's really yellow and there's almost no good sun here for at least about 2-3 months. I also tried some lamps that I read about but without any luck.

Your lens looks awesome and good job with the focus in my eyes!
12-21-2011, 01:27 AM   #3
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ok, that video is SCARY!!
12-21-2011, 02:03 AM   #4
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Original Poster
QuoteOriginally posted by mikeSF Quote
ok, that video is SCARY!!
Natiual thorium, although a low-level radioactive substance, is only an alpha particle emitter. Which means that as long as you don't ingest or inhale it, you should be safe as alpha radiation is blocked by a piece of paper. Most of the alpha particles come out the rear of lens and I'm sure they won't be able to reach your face when you're using the viewfinder.

Thorium - Wikipedia, the free encyclopedia

Quoting from Alpha decay - Wikipedia, the free encyclopedia

"external alpha radiation is not harmful since alpha particles are effectively shielded by a few centimeters of air, a piece of paper, or the thin layer of dead skin cells"

However, the video of the guy "fixing" a Super Takumar's yellowing by smashing is with a sledge hammer may have been a rather foolish thing to do if he atomised any of the thoriated glass and managed to breath some of it in. (The same reason in the old days that you were not supposed to "burn off" a thoriated gas mantle in an enclosed space.)


Last edited by dosdan; 12-23-2011 at 02:27 PM.

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