Re: 35mm lenses compared?(tech/optics)

[captyng@vtx.ch (Gerard Captijn)]

>Well Andrew, this will be a long answer to a complicated problem.
>First of all: why the change from two to one aspheric lens. Any aspheric 
>introduces two problems and splves a number of other ones. While 
>correcting some aberrations (Spherical aberration in particular and also 
>com.(the recent article about the 35mm Asperics erroneously only mentions 
>coma) it generates other faults. These however are quite difficult to 
>correct. The more aspherisc the more problems. Aspherics need very small 
>tolerances during the production stage. So more aspherics mean more 
>control at the production. 
>So it is quite sensible to try to reduce the number of aspherics.  From 
>the optical and production view the first version is more 'difficilt'than 
>the current one. 
>Your kind of testing must be quite inconclusive. Colour neg material is 
>totally unsuitable for lens testing (with the exception of the Ektar 25, 
>BUT then a high performance enlarger lens is imperative)
>Your 4x6 prints are too small to see the details, even with a magnifier. 
>And what you see is the result of the enlarger lens of the lab, And these 
>are notoriously off margin quite often. 
>And hand held shots can be misleading. See the two pictures in the 
>Viewfinder article referred to. Both pictures show elongated light 
>sources all over the field. From center to corner. The authors attribute 
>it to coma. BUT: coma is an off axis aberration and is only seen in out 
>of center areas. Therefore their 'coma' is presumably shaking of the 
>camera while shooting handheld. 
>The remark in that article that at f/5,6 both aspherics work fine is true 
>but totally uninformative. Every lens in the Leica stable, gives very 
>good to suberb results at f/5,6. The critical opening would be f/2,8 or 
>f/2,0. That separates the good from the bad. 
>Now to the performance of the 35mm ASPH. At 1,4 you are in Nirwana land: 
>the lens then exhibits a high contrast, very fine detailed image with no 
>traces of flare and extremely good suppression of halo around light 
>sources. This performance is a quantum leap above the old Summilux 
>1,4/35. At f/2.0 the performance of the ASPH is slightly better than at 
>1,4. In comparison the Summicron-M 35mm ( 7 element version) at f/2,0 is 
>the equal of the f/2,0 performance of the ASPH. From then on both lenses 
>are the same performance wise. 
>So if the maximum aperture is not absolutely needed the current Summicron 
>35mm is certainly the equal of the ASPH at apertures from 2,0. Remember: 
>apherics are needed to enhance performance in situations where high 
>apertures and/or large fields of view must be covered. 
>I really am eager to see what the announced 35mm Summicron ASPH will do. 
>Erwin Puts

Erwin, how right you are!

Gerard Captijn,
Geneva, Switzerland.
E-mail: captyng@vtx.ch
Fax: +41 (22) 700 39 28