Re: Resolution at long focal length settings

2

Ron Tolmie wrote:

Ian:

In my own experience with the ZS20 the resolution at the maximum focal length is substantially worse than at shorter focal lengths. You need to put the camera on a solid tripod and use the timer delay for such shots. Even with the smallest f/ stop the aperture diameter is still nearly 11mm at the longest FL so the image softness cannot be blamed on diffraction.

Hi Ron,

I'm disappointed that you didn't address the quote I posted in my previous reply. Here is a shorter quote from the same source:

"Diffraction thus sets a fundamental resolution limit that is independent of the number of megapixels, or the size of the film format. It depends only on the f-number of your lens, and on the wavelength of light being imaged. " (My emphasis).

So, just to reiterate, it is NOT the case, as you claimed (quoting your first post):

"Since the diffraction is inversely proportional to the diameter the diffraction effects are much less significant at long focal lengths."

In fact, the diffraction effects are very much just as significant at long focal lengths, and the diffraction effects are the same as for short focal lengths for a given f number.

I think you became sidetracked in talking about the way resolution can differ, and certainly does differ for the FZ and ZS cams, at different focal lengths with the same f number setting, quite apart from diffraction effects.

To take an example where diffraction is not a limiting factor on resolution, for the FZ35/38 I carried out detailed resolution testing at different f numbers and FLs as shown here .

The results show that at max zoom (486mm equiv.) and the widest aperture of f/4.4 (which is not diffraction limited) the resolution is lower than at full WA (27mm equiv.) and the same f number. However, and this is the crucial point, the difference in resolution is not due to diffraction, it is due to the lens itself. I think that is the source of your confusion, in addition to your incorrect statement quoted above.

BTW, for my testing I used Jimmy's (JC Brown) coloured Es test chart and I did, of course, use a tripod and the self timer, and with the OIS switched off. I also took replicate shots at each setting to ensure that my results were valid.

Ian