Oly 45 1.8 with Pana GTC1 converter... works !!!

Started May 17, 2012 | Discussions thread
Great Bustard Forum Pro • Posts: 42,285

Great Bustard wrote:

kenw wrote:

Great Bustard wrote:

It makes the lens a 90 / 3.6, which is equivalent to a 180 / 7.2 on FF. Big, big difference between a 90 / 3.6 and a 180 / 1.8.

As already discussed in the thread it is a front mounted teleconverter so it is not a 90/3.6 (which would be the case for a rear mounted teleconverter). It would be a 90/1.8 for a properly sized front mount teleconverter.

Interesting. So a front end TC changes the diameter of the entrance pupil? Makes sense, I guess, since the entrance pupil (virtual aperture) is the diameter of the iris (physical aperture) as it appears through the front element, thus it makes sense that a front mount TC changes its size.

However, in this case it appears the front element may be undersized for a 90/1.8 so it probably isn't quite that either.

The FE would have to be 50mm to make the 45 / 1.8 into a 90 / 1.8. Even then, however, it would be equivalent to a 180 / 3.6 on FF. Still pretty good, though!

Assuming the zoom pic of the GTC1 is accurate:


then given that the outer diameter is 53.5mm, the FE looks to be about 32mm. This, in combination with the 45 / 1.8, would make for 90 / 2.8 (90mm / 32mm = f/2.8) at best (still better than a 2x TC!), which would be equivalent to a 180 / 5.6 on FF.

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