Tests of Aperture with TCs

 


Testing of the Effect of Aperture with Teleconverters



Tests and Results


I tested my FZ35/38 with various TCs to compare exposure settings, so as to determine whether there was any change in exposure settings (brightness) with or without a TC attached to the cam.  I expected, as Jimmy's analysis shown above had predicted, that there would be no change.


I used A mode, f/4.4, centred weighted metering, and centre spot focus, at maximum zoom (86.4mm FL = 486mm as 35mm equiv.) indoors, with a tripod kept at the same position.  I took shots  under fluorescent lighting of a small newspaper clipping attached to a door.  I also measured the front (F mm) and rear (R mm) diameters of each TC.


Canon TL55 (1.4x): F 67, R 46

Ricoh 200M (1.5x): F 65, R 33

Nikon E15ED (shortened) (1.5x): F 51, R 31

Canon TC52B (1.6x): F 56, R 26

Nikon E17ED (1.7x): F 85, R 43

Olympus TCON17 (1.7x): F 72, R 35

Olympus C180 (1.7x): F 43, R 19


Below is a set of reduced size images from the cam without any TC and with each of the TCs in turn.  I also included the TCON17 with and without an annulus of cardboard cut so that it covered the rear element of the TC but with a central hole 20mm in diameter.


Set of Test Images


In every case the exposure settings made by the cam were the same: ISO 400, f/4.4, 1/6 sec.  Although the exposure was the same for all (metered from the central area), there were distinct differences in vignetting, and there were also some slight differences in WB.


The test with the cardboard annulus on the TCON17 demonstrates how reducing the effective diameter of the rear lens element increases the vignetting but does not affect the exposure of the central area of the image.  The variations in vignetting shown by the various TCs therefore indicates that those with narrower lens elements vignette more than those with wide lens elements.


Conclusion: For all of the TCs tested there was no change in effective aperture, as predicted.


Important "Take Home Message"

A front-mounted TC is a very useful addition to a Panasonic FZ digicam because, unlike a rear-mounted  TC on a DSLR, it does not lose any light and requires no change in f stops.  When using front-mounted stacked TCs there is also no loss of f stops, although the extra glass may degrade IQ and it is probable that vignetting will be worse.


FZ35/38 vs FZ100

An interesting aspect of this is that the FZ35/38 at maximum zoom (486mm), with the widest aperture of f/4.4, and using a good quality TC such as the E17ED, the effective aperture will be wider, the effective optical FL will be longer, and the IQ may be better, than using the FZ100 at its maximum FL of 600mm and its widest aperture of f/5.2.


For example, at max zoom using a 1.7x TC on the FZ35/38, the resulting optical FL is about 820mm and the widest available aperture is f/4.4.  This is a considerably greater FL than the FZ100 or  the FZ40/45 (600mm) and with a wider effective aperture - f/4.4 versus f/5.2.


The advantage of using an FZ35/38 with a TC rather than an FZ100 (or FZ40/45) is that the FZ35/38 has a considerable advantage in its widest available apertures while also being able to cover the same, or even greater zoom range.  Used without a TC the FZ35/38 is also smaller and lighter than these cams and offers just as good or perhaps better IQ.


If a TC is used with the FZ40/45 or the FZ100, extra support has been found to be needed, because the lens protrudes further than the Fz35/38 and the cam/TC combination has a greater length and weight.  People have reported needing to support the TC itself rather than simply relying on the tripod mount on the camera.  The FZ35/38 does not have this complication.




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