Working Distance with a TC

 


Extending the Working Distance of Closeup Lenses using a Teleconverter

I carried out some tests with the Canon 250D and the Sony M3358 achromats on my FZ35/38 with and without a teleconverter.  I used the Canon TL-55, which is a TC with a power of 1.4x and a 55mm thread.  I attached the TC to the front thread of the achromat using a 58-55mm stepdown ring.  I've shown a shot of the setup with the Sony achromat below.



FZ35/38 with Sony M3358 and Canon LT-55 attached.


Using a tripod I took shots of a ruler on a flat surface, so as to be able to easily determine the field width.  I measured the working distance (from the front of the LA3 adapter) with a tape measure.  I adjusted the working distance from the closest available autofocus to the furthest available autofocus for each achromat, both with and without the TC.  I repeated the tests at different zoom settings: maximum zoom (18x, 486mm equivalent), and lower zoom settings down to about 11x.


I plotted the results to yield a graph for each of the achromats, as shown below (click on the graph for a larger view).


Field Width versus Working Distance for the Canon 250D


Field Width versus Working Distance for the Sony M3358


It is clear that the TC did provide a much greater working distance for both achromats. 

For the Canon 250D at 18x zoom, the farthest focus was increased from about 30cm to about 50cm, and the nearest focus was increased from about 24cm to about 29cm. 

For the Sony M3358 at 18x zoom, the farthest focus was increased from about 35cm to about 61cm, and the nearest focus was increased from about 25cm to about 43cm.


Although the TC did reduce the magnfication somewhat for each achromat, this was outweighed by the advantage of the gain in the working distance, as well as the advantage of a considerable gain in the range over which focus could be achieved.


An interesting point is that for both achromats at 18x zoom, a greater magnification (smaller field width) was achieved at the farthest focus than at the nearest focus, both with and without TC; while at low zoom settings, the reverse was true.  For both achromats there also seemed to be an intermediate zoom setting at which the magnification did not vary much at all from the nearest to the farthest focus.  For the Canon 250D this was at about 12x zoom, and for the Sony M3358 it was at about 14x zoom.


It can be concluded that using the Canon TL-55 with the Canon 250D or Sony M3358 on the FZ35/38 is a practical way of increasing the working distance while still providing good magnification.  This TC is quite small and lightweight and does not make the setup inconvenient to use.



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