# ZS20 / TZ30 Users: Any tips on 'best' setting for shooting pictures?

Started Dec 30, 2012 | Questions thread
Re: Shoot WIDE OPEN, and at -EV

Hi Erik,

Possibly I'm wrong about this, but I think the effective aperture diameter figures for the ZS19/20 are, according to my calculations, as follows:
Effective aperture (that is, the diam in mm) = actual FL in mm / f number.

So, at max WA (24mm equiv.), the actual FL is 4.3mm, and that gives an effective aperture of 4.3/3.3 = 1.3mm at the widest available aperture setting (smallest f number) of f/3.3. At 24mm FL and f/8, the effective aperture is 4.3/8 = 0.54mm.

At max zoom (480mm FL equiv), the actual FL is 86mm, giving at the widest available aperture of f/6.4, an effective aperture diameter of 86/6.4 = 13mm. At this 480mm and f/8, the effective aperture diameter is 86/8 = 10.75mm.

At 480mm and f/8 on the ZS20, my resolution tests, which are given in full here:
http://www.ianperegian.com/My_FZ35_38_Webpage/ZS20_Resolution_Testing.html
showed that diffraction caused some visible "fuzziness" as can be seen in the chart image below:

﻿

However, the effective aperture as calcluated above was 10.75mm, and therefore much larger than the figure of 3mm which you have given.

Diffraction depends on the f number and the wavelength of the light, as I think is explained well here: http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm.

My resolution tests on the ZS20 seemed to show that the diffraction effect ("fuzziness") did not start to become visible until the aperture was narrower (f number larger) than about f/5.6. This tends to agree with the calculator given on the above site.

The maximum resolution did occur at or near the widest available aperture at a given FL and there was a decline in resolution as the aperture narrowed, but this is distinct from the diffraction effect and is due to the lens itself, I assume.

I think the difficulty of always using the widest available aperture at all FLs is that in very bright conditions the shutter speed may not be fast enough to prevent overexposure. I would think it is safe to use apertures as narrow as f/6.4 without worrying too much about loss of resolution/diffraction for general shots.

Ian

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