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Old 25th June 2019
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Re: New MC 20 announced.

Hi,

Basically a teleconverter is group of lenses that together act as a single diverging lens that enlarges the central part of the image obtained by the objective lens and then the central part is projected on the sensor. As example: say we use the 300mm F/4 lens. The front lens diameter is 75 mm. Adding the MC-20, 2.0 TC, would have as effect that what is captured by the central 37,5 mm of the lens are projected on the sensor. In effect you have achieved the same as doubling the focal length. And when doing so there are two negative side effects:
The well known is 3/4 of what the front lens captures have been "masked", only 1/4 of the lens area is used, which is 2 F-stops light loss.
The lens optical resolution capability is reduced. Larger lenses have higher resolution capability, size matters. Does this matter on the final results, what is captured by the sensor? Maybe, see further down.


Now, lenses are designed and manufactured with certain tolerances, resulting in imperfections. The implication of enlargement is that any imperfections in the lens will be amplified with a degree which should be more or less equal to the magnification. If the lens is designed and manufactured to very high standards, above the standards what the sensor is capable of capturing, then the effect of adding a TC may not be so detrimental.

If the lens is manufactured with lower standards then amplifying would mean that the impact of lens imperfections become more noticeable; losing sharpness and contrast. In addition to this could be introduced additional distortions, color shifts, chromatic abberrations caused by the teleconverter if the latter is of not so high quality. Adding a teleconverter is similar to adding one more telephoto group on a telephoto lens. If you know the details of the optical design and formulas of the lens, then designing a teleconverter that has good match and minimal detrimental impact is an easier task than if you don't have that information. I assume that Olympus have walked the extra mile when designing the MC-14 and MC-20 for a good match with the lenses that they are meant to use with.

As an example. Again, the m.Zuiko 300 F/4. Wide open.
Without teleconverter it is capable of resolving 68 lpmm which is excellent, enabling to take exceptionally sharp photos.
With the MC-14 the resolution capability drops to 55 lpmm. Still a very good value.
The MC-20 has not been tested yet, my guess is that the same test would give 40-45 lpmm. Future will tell...
NB. Above was measured with the E-PL1, I don't know the values that would have been obtained with the E-M1 M.2

On same site you can read about the 40-150 F/2.8, which with 67 lpmm is excellent too and where adding the MC14 lowers the resolution to around 47 lpmm at least at the centre of the image. I would guess that adding the MC-20 would result in lower 30's figure, and I would be hesitant using it without stopping down a step or two if sharpness is a primary concern.

Source: https://www.lenstip.com/lenses_reviews.html


On wikipedia is description of a teleconverter https://en.wikipedia.org/wiki/Teleconverter
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