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06-25-2013, 03:28 PM   #16
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QuoteOriginally posted by kcobain1992 Quote
Allow me not to agree with your methods.
I'll allow you once you have personally written a clear and practical guide how to adjust the focus on a takumar along with pictures, until then, sit back, buckle up, and be quite.

06-25-2013, 04:18 PM   #17
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Uhm.. did you miss my other post in this thread?
06-26-2013, 01:08 AM   #18
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06-26-2013, 03:23 AM   #19
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QuoteOriginally posted by bornamachine Quote
rear lens is stationary and is placed at a set distance inside the camera body and does not move
Incorrect, the M42 Takumar 35mm f/3.5 does not have a fixed rear element, the rear lens group moves in unison with the front lens group.

QuoteOriginally posted by bornamachine Quote
our lens is now sunk in the barrel as deep as it can possibly go, and that is the most infinity focus your lens can achieve
The travel of the helicoid does not indicate the point of accurate Infinity focus. For photographic optics Infinity is more correctly considered as a range, not a finite point. Anyone who has done astrophotography will be aware of this. If you have adjusted your lens in this manner, when focused at "infinity" your lens will incorrectly place the plane of focus behind the sensor, not exactly on it, as it is supposed to do when it is properly calibrated for infinity focus.

A properly calibrated lens when focused at infinity, the rear nodal point of the lens will be separated from the sensor by the same distance as the focal length of the lens*. Pushing the rear nodal point any closer than that accomplishes nothing.

QuoteOriginally posted by bornamachine Quote
Why this lens managed to focus and not the last one??? My theory: Takumar made 3 versions of this lens, first being able to reach f22, latter 2 reaching f16, the previous lens I had was a f22 lens and its rear lens protruded beyond the body further then this f16 version, and if you have read in my earlier post that when I unscrewed the rear lens by grasping it with pliers, and it brought the rear lens DEEPER into the body, the infinity focus worsened (Meaning it had to sit LESS DEEP to achieve infinity focus but unable to do due to lens design). You can see from the last picture that the rear lens of this f16 is sitting more flush with the body) Anyyway, that is my logical conclusion why the f16 is able to infinity focus on my K5 and the f22 was not.
wow. Has the possibility ever occurred to you that the other lenses were miscalibrated by previous owners or perhaps by accident? Sometimes the simplest explanations are the most accurate.

*though with an SLR this can sometimes be physically impossible therefore a retrofocus lens design is used to achieve a similar effect whilst having the lens physically further away from the imaging plane.

Last edited by Digitalis; 06-26-2013 at 03:48 AM.
06-29-2013, 10:22 AM   #20
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After working my way through this thread, I am making a mental note to avoid buying any used lenses from this person. Wouldn't it just have been easier to get a proper adapter rather than munge (perhaps improperly) the internals of a lens. One less good ST 35/3.5 in the world I guess.

06-30-2013, 01:54 AM   #21
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QuoteOriginally posted by stevebrot Quote
I am making a mental note to avoid buying any used lenses from this person
forewarned is forearmed - only a skilled pentax photographer should buy lenses from this person, people who are less squeamish about stripping a lens down. I am actually seriously considering doing a tutorial on how to do this* on many common pentax lenses (since I own so many of them). The upshot of this is that he will not be able to to sell the lenses for market value because of his butchery.

*including the process of separating and re-cementing lens elements

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