Archived posting to the Leica Users Group, 1999/06/01
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Don Post wrote: >Mary Grace: >Thanks for the info.... I was hoping to use it with a Summar, but since the >diameter of this lens is smaller, a proportionately smaller dot would be >nesessary- perchance, do you know the diameter of the Thambar objective? >Were all the Hektors pretty much uncorrected for spherical aberration? I >sold my Hektor 135/4,5 and kept the Elmar 135/4 because I thought the extra >bit of speed was the way to go and that the Elmar would be a better all >around lens- didn't think that the Hektor might be better for portraits! >Dan >-----Original Message----- >From: MGMcGough@aol.com <MGMcGough@aol.com> >To: leica-users@mejac.palo-alto.ca.us <leica-users@mejac.palo-alto.ca.us> >Cc: dwpost@email.msn.com <dwpost@email.msn.com> >Date: Monday, May 31, 1999 6:43 PM >Subject: (Thambar) Mary to Dan > > >> Dan m'boy - the spot is exactly 1/2" (12.5mm) in diameter, silver on one >> side & black* on the other --- but if not used on the Thambar, it has to >be >> glued to a clear or UV filter & then used with a large diameter lens of >the >> uncorrected spherical aberration type like the 125/2.5 Hektor - it is just >> not effective on most other lenses of smaller diameter & the f: stop has >> to be recomputed proportionally to the effective fl/dia ratio. Since the Thambar is an f2.2 lens, the entrance pupil would be about 41mm. The Summar similarly would have an entrance pupil of 25mm. So the proportional dot would be about 7.6mm in diameter. Might I suggest, though that to try this you use a larger dot, say 10 to 15mm in diameter. The Summar is better corrected for spherical aberration, so to see the effect you will need to cut out more of the central rays. If you use a 15mm dot, make sure you don't stop down past 2.8, and not past f4 with a 10mm dot, just so that you do let some light in :-). * Henning J. Wulff /|\ Wulff Photography & Design /###\ mailto:henningw@archiphoto.com |[ ]| http://www.archiphoto.com