Color filters to correct focusing issues with meniscus lenses

[Maris Rusis]

I've fallen into the opposite theory for landscape pictures using chromatic meniscus lenses and panchromatic or infrared sensitive film. The filter that always goes on is a #25 red. Why?

The stray part of chromatic aberration that strongly affects film is blue/violet but I don't see those wavelengths well and can't focus them confidently.
The red filter knocks the blue/violet out and transmits red which I see well and can focus accurately.

The red filter is also a good preview for the focus plane an opaque IR filter will deliver. Any error is small and is easily absorbed by stopping the iris down a bit.

Landscapes often have bright highlights and blue open shadows. The red filter deepens those shadows, raises apparent contrast, and as a bonus will darken blue sky and make clouds "pop".
I reckon this is good compensation for some uncoated, uncorrected meniscus lenses that natively deliver overly soft low contrast images.

[ridax]

I've fallen into the opposite theory for landscape pictures using chromatic meniscus lenses and panchromatic or infrared sensitive film. The filter that always goes on is a #25 red.

That's not the opposite theory, that's just the opposite practice. As posted above, I've addressed that topic in another thread.

Here I just talk on a very different topic. Namely, how to focus if one does not want to use any filters while taking the picture.