Re: [Leica] Degradation with filters

["Mike Durling" <durling@widomaker.com>]

Erwin:

Other than the effect on specular highlights that you mention, do the
filters you tested cause any measurable effect on the rendering of fine
details with various lenses?  I know that this has been controversial in the
past but I was interested in what can be measured on the test bench.

Mike D

- ----- Original Message -----
From: "Erwin Puts" <imxputs@knoware.nl>
To: "L U G" <leica-users@mejac.palo-alto.ca.us>
Sent: Sunday, November 05, 2000 9:37 AM
Subject: [Leica] Degradation with filters


> I conducted a numberof experiments to see if and under what circumstances
> the use of a filter could degrade image quality. In theory, when the
> surfaces are perfectly plane, the effect would be very small. Note that
the
> Apo-Summicron-R 2/180 has a permanent built-in filter in front of the
glass.
> Here we have perfectly plane surfaces and the computation of the lens was
> done with the filter effect incorporated.
> Generally we can expect some stray light and obviously some secondary
> reflections. These latter effects I will neglect for the moment. Stray
light
> and flare around specular highlights are the general degrading effects
when
> using filters. These effects are stronger  in situations with high overall
> contrast  and strong light sources in the image  and when the lens angle
is
> greater as then the skew rays are more troublesome to correct.
> In a coming issue of LFI there will be a lengthier article with comparison
> pictures to show the effect with and without filter.
> Here I will keep it short and note that the image degrading effects of
> filters do concentrate around bright spots in the image (flare and halo
> phenomena) and will be stronger when using lenses of wider aperture and
> wider angle of view and when the object has high overall contrast and
> intensily bright spots.
> On the other hand: a longer telelens at moderate apertures and objects
> without bright small highlights in dull or overcast weather will not show
> any effects at all.
> Provided the filter is really good and multicoated. Really good means
really
> plane surfaces that are very smooth as any irregularitiesdisturb the
passage
> of the rays.
>
>
> Erwin
>
>