Short break to Paternoster

Monday, 10 April 2023 09:10

Our day to day life has had a few knocks and bangs over the last couple years, and my wife and I hadn’t had a some quiet time away for quite some time. Paternoster is one of our favoured getaways; A quiet and small west coast fishing village just a couple hours drive north from Cape Town. It's the perfect place to get away and switch off, with high chances of finishing a book or two without getting distracted or bored. A place to clean up and recover from the daily toxins and corruptions that are Facebook, WhatsApp, Email, etc

I tried to use my Nokton 75mm f/1.5 ASPH as often as I could. I wanted to force myself to learn it’s characteristic. I feel it’s an excellent optic let down by a poor focus mechanism that is essentially too short in focus throw for a fast lens. It not only makes focusing accurately harder, but as I’ve come to learn, it exacerbates the mechanical slop or hysteresis between the optical assembly helicoid and the rangefinder linkage helicoid. A steeper faster moving thread increases the error when switching focus directions, and the tiny, and I really mean tiny, slop that the rangefinder helicoid experiences is enough to cause a significant back-focus when focusing in the direction from close range to infinity. 

This is essentially present in most M lenses. Some lenses, how I understand it, with a focal legth of around 50mm, only have one helicoid instead of two and therefore don’t have the focus to rangefinder coupling disparity when changing focus directions. Because the specific focal length of the rangefinder of M cameras is around 50.6mm (M10-R), some 50mm M lenses have either exactly the same, or very close to, this focal length and therefore need no adjustment to the focus ratio for the rangefinder mechanism, or only a slight cam that is machined into the lens’ rangefinder ring.

I’m going to say that the Nokton 75mm f/1.5 will be a better lens if the focus throw wouldn’t be so short, which would make focusing easier and more accurate, while also reducing the back focus error when focusing from the “wrong” direction. The focus throw is so short, that a subject 12 meters away, lands within the left side of the focus ring’s infinity symbol as seen in on the right...

The lens really forced me to chimp my images, constantly checking the rear LCD or Visoflex to check if my focus was right. This is counter productive behaviour to shooting with an M camera, and this lens really shows small focus errors in quite a pronounced fashion. For this reason I will probably sell the lens at some point, but this could take quite a while thanks to my location and the non-existent demand for M lenses here. 

The Summicron-M 50mm V is still easier to use, focus shift and all...