Comparison of Three Fujinon 250mm lenses on 8x10

[Kino]

Many thanks for the time,effort and expense to produce this comparison!

Very informative and useful to see.

[Vaughan]

Have you ever tried stacking any diffusion disks with the SF to explore intermediate softness, or is that just a recipe for halation soup?

The "strainer" disks don't cause the soft focus effect (I assume that's what you me an by diffusion). Quite the opposite, they restrict it. The soft focus is caused by spherical aberration from under-correction in the front half of the lens. The outer parts of the lens make an image that focuses further back than the central part, which makes it out of focus. Adjusting the amount of central image and outer peripheral image changes the amount of soft focus effect. Stop the lens down past about f11 and the soft focus effect is gone completely.

The strainer design allows control over the amount of light the lens transmits by selectively blocking parts of the aperture. The central part is unrestricted because that's the main (sharpest) image, while the circular holes around the periphery of the aperture allow the out-of-focus image through. The yellow dot strainer allows more peripheral light through than the red dot strainer. Combining strainers would result in an image that would be about the same as the red dot strainer, or if the combination blocks more peripheral light the image will have less soft focus effect. Certainly not more.

For a better idea of how the strainers work, look at the Rodenstock Imagon lens. It's strainers are adjustable, and doing so closes off some off the holes on the periphery which reduces the soft focus effect.

[xkaes]

Not to mentions that you can only use one grid at a time.