Telecentricity in Micro Four Thirds.

Started Oct 30, 2013 | Discussions thread
Joel Halbert
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Re: Olympus patent for telecentric lens
In reply to SHood, Oct 31, 2013

SHood wrote:

You can see from this patent that Olympus was looking at doing a 15mm f2 telecentric lens. I doubt we will see this now but we may see other designs come to fruition.

http://www.43rumors.com/olympus-15mm-f2-0-patent/

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I'm not clear why the patent depicts a particularly telecentric design. The drawing shows the sensor to be somewhat larger than the exit pupil; as pointed out in this thread a larger exit pupil would be a necessary (though not sufficient) condition for a completely telecentric lens design.

It does appear to be a retrofocus (inverted telephoto) type of design; those are more likely to achieve long spacing between lens and image plane, and thus tend to have more perpendicular incidence on the sensor.

It is the near-perpendicular incidence, not so much the other useful attributes of telecentric lenses, that was the primary benefit of Olympus' Four Thirds system emphasis on "designed for digital" lenses. However, the problems associated with off-axis incidence have gotten much better since the beginning of Four Thirds, and of course the near-telecentric requirement plus the mirror-compatible spacing requirement kept the lenses from being as small as we see today with M43.

Most digital sensors today still have some issue, though not as much, with extremely off-axis image rays. I think the M43 lenses strike the right compromise for now; Four Thirds was the right spec at that time. M43 also is more cognizant of software correction methods which are an essential  and beneficial component of modern camera/lens systems.

In the future, when sensors may become nearly as tolerant of off-axis rays as film emulsion is, then the right compromise might be in the direction of high quality but very compact lens designs like many Leica RF lens designs. However, there are other issues with those aside from the angle - they are not particularly designed for focusing by fast and light AF motors; they aren't necessarily suitable for OIS implementation; they may be extra-sensitive to production mechanical tolerances.

In my view, though it is interesting to track and understand the design approaches, the lenses and cameras should be judged on what performance they deliver, at what cost and with what covenience and flexibility in use. Telecentricity is good to know about but should not be a particular "goal" of most lens buyers.

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JoelH

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