Testing of the FZ35/38


In this section:

1. Testing of FZ35/38 Resolution with Aperture and Focal Length

  1. 2.Testing of FZ35/38 Resolution with ISO Setting

  2. 3.FZ35/38 JPEG Compression

  3. 4.FZ35/38 Available Apertures versus Focal Length

  4. 5.FZ35/38 with Teleconverters

    Teleconverter Table of Results

    Stacked Teleconverters

    Stacked Teleconverters with a Closeup Lens

    Effect of Teleconverters on Aperture

  1. 6.FZ35/38 with Closeup Lenses

    Extending the Working Distance using a Teleconverter

    Closeups of Oil and Water Droplets

  1. 7.Filters for Sun and Moon Images

Testing of FZ35/38 Resolution with Aperture and Focal Length

Various review sites publish resolution figures for digicam models but they are usually measured at a single, mid-range focal length and a single mid-range aperture setting.   There has been discussion on the DPR Forum about whether the Panasonic FZ superzoom models have a “sweet spot”.  For a typical camera lens the sweet spot is the particular aperture setting where the resolution is highest, and this is often found at mid-range of aperture.

Recently, an Australian review published Imatest graphs for the resolution of the FZ35/38 which showed that there was no sweet spot over the range of focal lengths tested:


Instead, maximum resolution was found at widest apertures and the resolution decreased as the f number increased, with the lowest resolution being found at f/8.  However, only focal lengths from 27mm up to about 250mm (35mm equivalent) were tested in the review.

Purpose of the Testing

My aim was to find out whether this pattern of decreasing resolution with increasing f number also applied to focal lengths above 250mm and up to the maximum zoom of 486mm for the FZ35/38.


As I didn’t have access to Imatest I needed a simple method of evaluating the resolution visually.  The usual resolution test charts for digicams incorporate sets of black narrowing lines but these are hard to evaluate reliably by eye.  Fortunately I was assisted by DPR Panasonic Forum member J C Brown, who has developed a chart similar to those used for visual acuity examinations.  Dr Brown very kindly provided me with a copy of his chart, which consists of rows of progressively smaller coloured letter “E”s, as shown below:

Although this chart was intended to determine the resolution of different colours, I used it to provide a means of visually estimating the resolution of the black letter Es, since the review charts only consider black.  Because the testing site I had available to me was limited in length, I printed the chart so that the reference line was 75mm in length instead of 100mm.  This enabled the distance from camera to chart to be correspondingly shorter.  I found that I was able to make a print of this smaller chart using my inkjet printer set at highest quality so that the smallest row of letter Es was still very sharply defined.  With my FZ38 set up at the correct distance from this chart, the 75mm reference line covered a length of 400 pixels on the sensor with the camera set at a particular focal length.

For comparison purposes I also printed a chart with black narrowing lines at such a size that the reference line on this chart covered 500 pixels when aligned at the same distance as the Es chart.  The numbers on the chart when multiplied by 100 then indicate directly the resolution in LWPH.  This narrowing lines chart is shown below:

I printed several copies of each chart and attached them to a backing board so that they covered the image centre and edges/corners.  A rectangular border was applied with dark tape to exactly the define the image area.  I also included three copies of a concentric circles chart but ultimately they were not found to be useful.  A photo of the finished board is shown below:


With the chart board mounted vertically on a wall, I set up the FZ38 on a tripod and moved it so that at a particular focal length setting, the image of the white chart board area exactly filled the LCD screen.  It was a slow and painstaking process of making very small adjustments to the tripod until the reference line on the centre narrowing lines chart covered 500 pixels on the sensor image, to within about 1%, with the camera set to 12MP resolution.

At each particular focal length I took shots at every available aperture setting using A mode, AWB and 100 ISO.  I used ISO100 in preference to ISO80 since review tests have shown that ISO100 gives a very slightly higher resolution than ISO80.  I also used exposure bracketing since it was important that the exposure was optimised.  The best exposure was generally in the region of +2/3EV to +1EV.

Absolute Resolution

The absolute resolution is defined as the position along the narrowing lines chart at which the lines can still just be clearly distinguished.  As this is difficult to do from the narrowing lines chart by eye, I used as a reference point the smallest row of Es in which the black E was just distinct.  On the Es chart, the row of Es marked 1.5 pixels represents a resolution of 2000 LWPH for the FZ35/38.

Extinction resolution

The extinction resolution is defined as the position along the narrowing lines where the black lines disappear completely and become a solid grey.  The region along the narrowing lines between the point of absolute resolution and where extinction resolution occurs, represents the zone of partial detail.

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J C Brown Test Chart