150 G-Claron info needed

[Pete Roody]

It covers 5x7, not 8x10.

[Darryl Baird]

I have (copies of) two different versions of G-Claron brochures. In the most recent I have, it lists an image circle of 284 at f/22 at 1:2 reproduction (distance?). My question is, how far from the (focused) lens is something at a ratio of 1:2?

I'm headed to the basement to look for a couple of books that might have the answer, but just in case... you guys with the bigger brains might have an answer.

[Pete Watkins]

I have a late 150 G-Claron that I bought new from Robert White about 7 years ago and I love it. Yes, it's f9 but on holiday last year with my beautiful B&J 4x5/5x7 I used only the 150 and my 203 f7.7 Ektar and I had a great time with very satisfactory negs. Go for a late one and you won't regret it.
Pete.

[Emmanuel BIGLER]

From Jim :
That 64° spec was to hold the modulation transfer function specs to a tolerance that graphic arts printers required.

Agreed ! But the guys in the Old World have alwys been very conservative, not like in the US where they are all revolutionaries

Not kidding : Same conservatism for the official specs of the apo-ronar, listed @48° but useable as a standard focal length ~ 53 degrees.

From Darryl :
My question is, how far from the (focused) lens is something at a ratio of 1:2?

Simple ! No maths required

let M = magnification ratio = (image size) / (object size ) = 1:2 = 1/2 = 0.5

here, focal_length = 150 mm

lens-to-subject distance is (focal-length) x (1 + 1/M) ; for M = 1/2, we get 150 x 3 = 450 mm

bellows extension beyond the focal plane : ext = M x f = 150 /2 = 75 mm

total bellows length (for most quasi-symmetrical lenses including G-clarons)
D = (1+M) x focal_length = 150 x (1.5) = 225 mm

Useable image circle in macro, approx, : C =~ C_infinity x (1+M)

C_infinity = 2 x (focal_length) x TAN (Angle/2)

example C_infinity = 190 mm, C (@ M=1/2 ) = 190 x 1.5 =~ approx 285 mm