[Leica] Re:Noctilux abberations?

[kididdoc at cox.net (Steve Barbour)]

On Mar 24, 2006, at 3:26 AM, Deveney, Marty ((PIRSA)) wrote:

>
> Hi,
>
> Ted wrote:
>> I've used a Noctilux since it was available in Canada, '72-73? And  
>> at times it was - is my main lens indoor and out.
>> However I was never aware of this condition. Is this something  
>> I've missed all these years that's good, bad or ugly?
>> Serious question.
>
> I love my Nocti.  I've shot a hundred or so rolls through mine  
> since I bought it from George Lottermoser in January 2005.  it's  
> the same version as yours Ted, the 58mm filter thread one that came  
> with a separate hood.
>
> You've raised something interesting here Ted - all lenses have  
> aberrations, it's just a physical fact of optics.  Even the Leica M  
> asph lenses (probably better corrected for aberrations as a family  
> than any other group of lenses current manufactured for cameras)  
> and the 50/2 Summicron (a very well-designed lens with conservative  
> specifications)  have them, you just have to know what to look  
> for.  With these lenses, most of the time most of these aberrations  
> hardly matter (in a well-designed, adequately constructed lens) and  
> are completely invisible to most viewers (who don't know what  
> they're looking for).
>
> The Noctilux is another story.  As Erwin Puts points out, wide  
> open, the Noctilux displays coma, spherical aberation and chromatic  
> aberrations from an image height of 9mm outwards at full aperture.  
> He also notes 'some inward bending curvilinear distortion' in  
> addition to the vignetting or light falloff that is quite  
> pronounced.  These are, to some extent, inevitable when designing a  
> lens this fast.
>
> But what does all that mean?
>
> Coma,
> http://hyperphysics.phy-astr.gsu.edu/Hbase/geoopt/coma.html
> http://en.wikipedia.org/wiki/Lens_(optics)#Coma
> otherwise known as oblique spherical aberration, makes bright  
> sources near the edge of the field look like a comet with a tail  
> rather than a single spot.
>
> Spherical aberration
> http://hyperphysics.phy-astr.gsu.edu/Hbase/geoopt/aber.html
> http://en.wikipedia.org/wiki/Spherical_aberration
> occurs because spheres are not the ideal optical surfaces (this is  
> why aspherical lenses perform better if properly designed) and  
> results in softness or blurring.  If you take a photo of a sheet of  
> newspaper under a sheet of glass with a Nocti (actually somewhat  
> more instructive than it may seem at first), it will be softer at  
> the edges than in the centre.
>
> Chromatic aberration
> There are several kinds of this.  The most common and the one the  
> Nocti suffers most from is described here:
> http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/aber2.html
> http://en.wikipedia.org/wiki/Chromatic_aberration
> where the lens bends different colours of light to differing  
> degrees.  It results in strange colour effects with colour films  
> and a loss of sharpness in B&W.
>
> 'Inward bending curvilinerar distortion' simply means that if you  
> take a picture of a brick wall square on with a Nocti at f1, the  
> bricks at the top and the bottom will look like they're curving in  
> towards the centre of the image rather than as straight lines.   
> This is often called 'barrel distortion' presumably from the  
> corresponding outward bending aberration's propensity for making  
> things that are composed of straight lines look like a barrel -  
> fatter in the middle and thinner at the edges.
>
> The vignetting or light falloff is an optical inevitability of the  
> speed of the lens.  Despite the extremely high refractive index of  
> some of the glass used in the Nocti (the higher the index the more  
> the glass can bend light) the edges of the lens simply can't  
> transmit the same amount of light from the edges of the field to  
> the edges of the film frame.  In the case of the Nocti it is  
> definitely optical vignetting (of this type) as opposed to physical  
> vignetting where the barrel or lens hood gets in the way of the  
> edges of the field.
>
> The Noctilux is a truly magnificent design.  There are fewer  
> aberrations wide open in the 55/1.2 asph breechblock lens for the  
> Canon FD cameras, in the 58/1.2 Noct-Nikkor and of course in the  
> 50/1.4 asph leica-M lens.  Wide open, even the original 1.2  
> aspherical Nocti performs better in some respects.  All these  
> lenses are, of course, also a half to a whole stop slower.  Any  
> lenses as fast or faster than the Nocti that have been manufactured  
> are inferior.  The Canon EF 50/1 is the closest in performance, but  
> it still lags behind in many areas.  it's also about the size of a  
> piece of telegraph pole (well, maybe not, but if you think the  
> Nocti is big, the Canon is huge).
>
> It would be possible for Leica to design an asph version of the f1  
> Nocti that would improve the performance relative to the current  
> version.  While the current Nocti is astoundingly good, lens  
> design, glass manufacture and (especially) methods for making  
> aspherical elements have improved enormously in the last 20 years.   
> Such a lens would probably be entirely unaffordable and anyone  
> hoping for a 50mm lens with the least number of aberrations should  
> buy a 50/1.4 asph.
>
> That ended up way longer than I intended . . . hope it was useful.

very useful Marty, and thanks very much.  I will add this piece to my  
file...

bottom line... the lens works well in the dark and in any light...  
giving wonderfully lucid images that don't fail to amaze me...

Steve




>
>
> Marty
>
>
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