View Full Version : APO Ronar as convertible

Steve Clark
1-Apr-2002, 21:10
Armin, Please post your findings, It will be interesting to read what you discover. Steve

Thilo Schmid
2-Apr-2002, 05:27

the Apo-Ronar has a strictly symmetrical design. Using either front or rear element will yield a focal length close to 600mm (not exactly, because of the spacing between the two elements). However, do not expect too much from this. The better the correction of a whole lens, the worse it performs "in half mode". The two elements are desgined to cancel the aberrations of each other.


Paul Schilliger
2-Apr-2002, 05:42
Ditto, Thilo. Armin, I had tried to separate a 360mm. The image was difficult to focus at full opening but the aberration was partly corrected at f22-32. The image center was pretty sharp, bu t rapidly softened toward the corners of a 4x5". The back element needs bellows much longer than the front ele ment for approx. the same image. Color fringing was noticable.

Jason Greenberg Motamedi
2-Apr-2002, 12:56
In conection, does anybody (other than Mr. Grimes) know how to calculate the new aperture on single elements? Is there any sort of equasion so I can play with single elements without shipping to RI? Sorry for my ignorance--Last time I took an optics or physics class was 22 years ago!

Paul Schilliger
2-Apr-2002, 13:04
By the way, the Fujinon A series make good convertibles. They are six elements. But careful when experimenting: it's easy to drop a small piece!

Jason Greenberg Motamedi
3-Apr-2002, 00:12
In an answer to my own question, apparently < fstop= focal length / diameter > so in the case of Armin's lens, f64=300mm/4.69mm, so assuming (I guess one would have to measure distance from the lens to ground glass to be sure) that a single element has a focal length of 600mm, the marked aperture of f64 would now be f128 with the ?new? lens (f128=600mm/4.69mm). Does this appear correct?

Paul Schilliger
3-Apr-2002, 07:48
Jason, this is probably not a big help, but when I made some trials I simply add ed two stops to the nominal value when the single element focal length was twice that of the original lens. The re sults were OK but perhaps not precise.

Paul Schilliger
24-Apr-2002, 08:03
Hi Armin! Any test made yet?