Heliar aperture scale

[Gene McCluney]

I've got an old aluminum barrel Heliar 300mm (30cm) lens. The aperture scale is f4.5, 6.3, 9, 12, 18, 25. Is this directly interpreted in-between the modern lens markings, or is it to another standard? If this is another standard, what would be the modern equivalent markings?

[Bjorn Nilsson]

That should be the same standard, just other openings, which are directly related to full stops from the f/4.5 opening. (They are all 1/3 stop above the usual 4, 5.6, 8, 11, ...)
On my pre-WWII 21cm Heliar, the barrel have 2 scales, one like yours and one with the "usual" scale on the other side.

//Björn

[Ole Tjugen]

That's a very common scale on pre-WWII German lenses. Lenses are still made with maximum apertures corresponding to that scale, mostly f:9 repro lenses.

The scale is completely equal to the "modern" scale, with 1/3 stop offset.