Pentax 125SDP – 2

Finally I had the chance to make the star test after the series of the stormy west coast weather. The result was great as expected.

The focal plane was around 215mm away from the end of the drawtube. So as predicted, I can add ESATTO 3″ in-between. The only pain is further heavy….

Anyway, it was great optics along with OHARA FPL-53 and FPL-51 which were still produced in Japan. So they were so expensive elements that time.

And the key design is that 1st and 2nd elements are widely separated. This gives the designer more options. But it requires higher level of machining quality and building-up skills. I applaud Team Pentax already did 20-30 years ago.

This is a page scanned from one of Tenmon-guide pages published a long time ago. As shown below, the g-c lines are gathered within 0.1mm or less. And meridional and sagittal look close each other. So we can expect the good and clean star shape the entire of the sensor. Keep in mind, 0-44.0mm is radius. So just half in today’s full frame sensor.

And my result seemed to be just like that. The scope was made more than 20 years ago? But it seems to be nothing obsolete.

I was told in the past the optics could somehow handle NIR too. I’m looking forward to seeing the result along with IDAS’s recently released GNB filter.


~ by tedishikawa on January 23, 2023.

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