Testing  of  the  ZS20/TZ30


In This Section:

  1. 1.Determining the Widest Available Aperture for Each Setting of the Zoom on the ZS20/TZ30

  2. 2.Testing the Resolution of the ZS20/TZ30

  3. 3.Comparison of the ZS20/TZ30 and the FZ35/38

  4. 4.The ZS20/TZ30 and Noise Reduction

  5. 5.Still Images Examples from the ZS20/TZ30

  6. 6.Macro Images with the ZS20/TZ30

  7. 7.Movies with the ZS20/TZ30

  8. 8.Low light video with the ZS20/TZ30

  9. 9.ZS20 with iResolution and iZoom

  10. 10. P Mode and iISO with the ZS20

  11. 11. ZS20 with Teleconverters

  12. 12. The ZS20 used as a “Microscope”

  13. 13. ZS20 Colour Contrast Resolution Testing

Determining the Widest Available Aperture for Each Setting of the Zoom on the ZS20/TZ30

The ZS20/TZ30 has a touchscreen interface which allows an alternative way to set the zoom to using the zoom lever.  There are two slider controls on the touchscreen, one for slow and one for fast zooming.  I found that it was possible using the slow zoom control on the touchscreen to set the focal length (FL) to each of its 45 positions.

By setting the camera to Aperture Priority (A Mode) and to the widest aperture of f/3.3 at full WA (24mm equivalent) then gently increasing the zoom, the focal length increases in steps, with the widest available aperture at each step.  I took a shot at each zoom setting and from these shots I was able to determine the exact FL (mm equivalent) at each zoom setting from the image EXIF data.

From the data I constructed a table for the 45 zoom settings as shown below:


The table provides a way to exactly set the ZS20/TZ30 to a precise FL.  By using the slow zoom control, the desired FL is obtained by slowly zooming to the zoom factor shown beside it in the table.  For example, if the FL setting of 249mm is required, the zoom is set to show 10x on the LCD screen.  For the low zoom factors having more than one FL setting, it is necessary to zoom to the factor immediately above or below and then count the steps until the required FL is located.

I used the data from the table to plot the widest available aperture (f number) versus FL, as shown below (click on the graph to view a larger version):


It can be seen that the f number increases fairly rapidly up to about 100mm FL, and is then fairly constant around f/5.4 from about 100-180mm, then rises slowly again, becoming constant at f/5.9 from 289-386mm. After that there is again a steady increase in f number to the maximum zoom setting of 480mm.

At the 386mm FL setting, the widest available aperture is f/5.9. That is the same as the ZS15's widest aperture of f/5.9 at its highest zoom setting of 386mm.

In the above graph, the use of f number, which is not linearly related to stop number, makes the change in aperture appear more steep than the actual change in stops.   Below is a table showing the relationship between f number and stop number over the range under consideration:


I therefore replotted the data using stop number versus FL, as shown below (click on the graph to view a larger version):


Looking at this graph, over the entire zoom range from 24mm to 480mm there is a change of 1.90 stops.  There is a rise of 1.3 stops from 24mm to 90mm, a slower rise of 0.36 stops from 90 to 290mm, a plateau from 290-386mm, then a rise of 0.24 stops from 386 to 480mm.

In comparing the ZS20 with the ZS3/TZ7, which has a zoom range of 25-300mm (12x) and a widest aperture range of 3.3-4.9 (3.45-4.59 stops), the extended zoom range of the ZS20/TZ30 of 24-480mm has incurred a penalty of just (5.35-4.59) = 0.76 of a stop.

Since the reviews consider that the noise is better controlled in the ZS20 by 1-2 stops over the previous model, it seems that this compensates to a large extent for the more limiting aperture range of the ZS20.

Note: The above table and graph for widest available apertures also apply to the later ZS30/TZ40 and ZS25/TZ35 models as well, since all these models have exactly the same lens, zoom range and available apertures.

These results have been discussed on the DPR Panasonic forum at:


Continue to Resolution Testing of the ZS20/TZ30

Continue to Macro with the ZS20/TZ30

Continue to AVCHD Video from the ZS20/TZ30

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