Modern 50 f/2 at infinity

[sjt1]

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I have two 50 f/2 summicron lenses - one I bought new in 2002, and another I bought second hand, but was made in 1979 (from the serial number). The 2002 one got most use until recently when I noticed the edges were very soft on far objects, even when the lens focus is set to the infinity stop. The strange thing is that the middle of the picture is that far obects are good as I expect them to be!

 

I set up a test. On a clear day I went to the top of a hill, where you can see for about 12 miles. The camera (M9) was put on a heavyish tripod and a cable release was used. For both lenses, I used the same procedure:

• focus set to infinity stop (rangefinder not used to focus)
  
• start at f/2 and go down to f/16, taking a picture every stop
  
• Camera set to aperture priority
  
• above procedure repeated a few times for each lens to give a decent set of pics to choose from
  
• mild sharpening was applied in LR, to emphasise what was in focus and what was out of focus (I still have the unsharpened versions and the results are consistent with the sharpened versions)
  
• To remove any effects of camera shake even when on tripod, I used a range of ISOs as well to keep the shutter speeds high - I ran through all stops at 160 and 640 a few times each.
  

 

Results for objects at infinity (about 6 miles away)

1979 lens

• f/2 - f/4 good in middle, edges not so good
  
• f/5.6-f/8 - very good in middle (very slightly not as good as 2002), edges very good
  
• f/11 - slight drop off in sharpness over whole frame from f/8
  
• f/16 - noticeable drop off in sharpness over whole frame form f/11
  

2002 lens

• f/2 - f/4 very good in middle, edges TERRIBLE!
  
• f/5.6-f/8 - middle excellent, edges still bad, edges considerably worse than 1979 lens at equiv stop
  
• f/11 - softer than f/8, edges still not as good as anything the 1979 lens can do
  
• f/16 - softer than f/11, edges still not as good as anything the 1979 lens can do
  

 

Using LR's compare tool, I could put a pic from the 1979 version and the 2002 version at the same stop and shutter speed on the screen in one go. This let me see the differences between the two.

 

As I said, all notes above are for objects a long way away, and the lens focus set to the infinity stop.

 

On the 2002 lens I also noticed that objects closer to me (say about 10m) were much sharper than on the 1979 lens, even when the lens focus is set to infinity. I think this is the crucial thing - I reckon the 2002 lens is not quite achieving inifnity focus, since the near objects are sharper than far ones, even when the lens focus is set to infinity.

 

Having said this, on the 2002 lens with the focus also set to infinity, the centre of the picture has far distant objects also in focus, resolving more detail than the 1979 lens in the middle. At the best stops (f/5.6 and f/8), there is a noticeable transition in sharpness between the centre and edges of objects for the 2002 lens - at the edges it gets all smeary.

 

All this leads me to some conclusions:

1. The 2002 lens is not quite getting proper infinity focus.
   
2. The there is some small field curvature that means the plane of focus favours closer objects at the edges, but more distant objects in the middle.
   
3. I think because the 2002 lens is not getting infinity focus, the field curvature comes into play and we get these errors.
   

 

My overall conclusion is that the 2002 lens needs adjusting to get its infinity back. I think then it would outperform the 1979 version (which is still very good indeed).

 

This leads me to some questions:

• Anyone (particularly lens experts) care to comment on these findings?
  
• Are the 50/2 lenses prone to field curvature?
  
• Are there any other interpretations given the results?
  
• Any idea who could fix the lens in the UK? Hopefully it will not be expensive!
  
• Can the optical part of the 2002 50/2 be unscrewed from the focusing helical? I understand the optical part of the 1979 version can be unscrewed like this.
  

 

Thanks in advance and apologies for the long post - I wanted to get all the info I could think of in at the start.

[cbretteville]

Steve,

It sounds about right that your 2002 needs a little attention. Have a look here for someone in the UK.

 

http://www.l-camera-forum.com/leica-blog/leica-repair-specialists/

 

You don't post the serial number of your 1979 lens, but that was the year the current 50/2 formula was launched. #2909101 is according to my sources the starting serial number for the lens. After that the optical formula has stayed the same, but it is thought that coatings may have been altered over time. Leica doesn't say one way or another. The mount changed to the current one with the extensible hood in 1994. So you may actually have the same lens in two mounts.

 

Carl

[lct]

+1 also the main weakness of the Summicron 50, as well as pre-asph Summicrons in general, is their relative softness on edges and corners at f/2. A good CLA will restore your lens as good as possible but you'll have to wait for the asph version, or acquire a Summilux asph, to get good results on edges and corners at f/2.