Hermagis 15" - coverage?

[Jerevan]

Hello lens-huggers,

do you think a 15" Hermagis would cover 8x10" (or 18x24 cm)? Preferably wide open but otherwise stopped down a bit (say f11 or so)?

[Ole]

15" Hermagis what?

Hermagis made lots of different lenses; with coverage anywhere between 10° and 110°.

Mine is a "Trousse Aplanatique", an Aplanat casket set.

If it's a 15" Rapid Rectilinear / Aplanat type, it will cover.

[Jerevan]

Yes, I figured I was trying get away with it. The particular one I drooled over, is an Aplanat no 4.

[Ole]

An Aplanat No. 4 should cover 24x30cm at moderately small stops, and 18x24cm with some movements wide open.

[Jerevan]

Can I assume it is as big and heavy as a small truck? I've no idea what I am getting myself into...

[Ole]

No, it should be about 6cm in diameter and 10cm long:

15" = 15x25.4mm = about 380mm

380mm / 7.2 (aperture of a fast Aplanat, most in that size are f:7.7) = 52.8mm

Add a little for barrel and hood (?), and you get about 6cm diameter. Aplanats tend to be about 1.5 times as long as they are wide, although there are large variations. I think most of Hermagis' lenses are shorter than this.

So 6cm wide by 10cm long is really the upper limit.

[Jerevan]

Ah, that's what math skills are for... Thanks a lot, Ole! You are a true lens-hugger, indeed.