Will scratched heat filter reduce sharpness, contrast on slide-projection?

I have been able to borrow a 6x6 slide projector, made in the late

1950's. The lens is a 135 mm from "Wetzlar". I am dissapointed with

the result, in terms of projected sharpness and contrast. The slides themselves are both sharp and contrasty when examined with

a Schneider loupe. When looking through the projector lens, using it

as a "loupe", it also seems to be rather sharp. However, there is a heat

filter in the projector that has scratches and irregularities. Since

the heat filter is placed after the projector lamp and after the

condensor (which is in good shape), and BEFORE the glassed slide

mount, can it have any effect on the projected sharpness and contrast

or will it only decrease the "light-output"? Or am I forced to

recognise that the optics of the 1950's slide projectors were of

poor quality?

The scratchy heat glass will mainly affect overall brightness and uniformity of illumination. Lack of sharpness and contrast can probably be blamed on the "Wetzlar".

Thanks Tim, I suppose it is that Wetslar then. So no cheap solution

within reach like having an optician polish the heat filter. A real

shame, the Hasselblad PCP80 is $$$$$ and this one is for free :-)

Maybe you can find an old view camera lens to cobble in it's place. That and judicious use of flat black paint.