[Leica] Monster High-tech 50mm 1.4 from Sigma and everyone else - distortion

[freakscene at weirdness.com (Marty Deveney)]

DaveR

>how important is distortion for photography outside of architecture?

All lenses display some residual distortion and all are loaded with 
aberrations if you know what you're looking for.  Distortion is as important 
as you make it.  Many people don't notice it some who do don't care about 
it.  If you can see it and it bugs you, it matters.  One thing that does bug 
me is something that the pre-asph 35/2 Summicron-M IV does: if you put a 
head or spherical object in one corner, it makes it more oblong than a 
retrofocus 35mm lens would.  The 35 asph and aspherical lenses don't do 
this, but they have their own foibles.  Pronounced curvature of field also 
irritates me.

>Secondly, is there much sample variation in modern lenses (my assumption
>would be less than in the past, but sometimes I wonder)? 

I can only judge from performance because I haven't tested dozens of lenses 
of the same type, but it seems to me that sample variation is lower than it 
used to be.  This figures with modern manufacturing and QA techniques.  I 
also assume that the more expensive a lens or a family of lenses is, the 
lower sample variation will be - Leica lenses appear to have exmplary QA 
with very little sample variation, while Nikon and Canon clearly apply more 
stringent QA to their professional lenses and less to their mid-range and 
consumer lenses.  I don't know about third party producers like Sigma.

>Finally, are lenses today really any better overall than lenses from say 25 
>years ago
>-- or are they just better in some ways, at the expense of other ways?

Optical performance has improved markedly.  Coatings and glass are better, 
manufacturing techniques have allowed technology that deals with optical 
aberrations better (like aspherical elements) to be easily incorporated into 
lenses and glass tpyes are evolving and improving all the time.  Plastics 
are more thermo-stable within their operating range than metal and are 
lighter.  lubricants are always improving.  These things all make a 
difference.  About the only thing that modern lenses in general won't do 
that many older ones can is last a lifetime.  The value of that depends on 
whether you want the performance now, or the object later.

>I don't shoot any architecture anymore, though at one time I did. I know
>that for me to notice distortion now, a lens has to be pretty bad. I can
>also live with a little barrel or pincushion, because in a critical
>situation I can fix it with software. But the moustache distortion found
>in some multi-asph consumer grade zooms (I haven't seen it in primes,
>but I haven't bought any new primes in a long time) is impossible to
>correct.

It certainly is hard to correct wavy distortion.  All these kinds of 
aberrations are balancing tricks for designers.  But it's always worth 
keeping in mind that the first things a designer considers after the basic 
lens specifications (i.e. I'm designing a 50/1.4) are the price the lens 
will sell for and how big it can be.  There's a lot of obsessing about 
distortion in cheap zooms on the web.  It's easy but expensive to avoid.

One of the things Leica is rarely congratulated on as much as they should be 
is the performance/size ratio.  Their current M lens lineup is optically 
exemplary, all the more remarkably so when you consider how small the lenses 
are.  

Marty


Gallery: http://gallery.leica-users.org/v/freakscene


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