Focusing a Nikon 50mm f/1.2 Ai-S (at f/1.2) on Nikon DF

I have a really neat manual focus Nikon 50mm f/1.2 Ai-S on a Nikon DF.

 

I have no problem focusing this (using Nikon's green arrow/dot focusing points) manually at f/3.5 or larger (which looks incredible). However, when I try to open this up at f/1.2 - 2.0 I miss 90% of the shots because they are out of focus even if the green dot focus point says it is in focus.

 

Other than swapping out the focusing screen to a split focusing system, is there a way to more reliable way to focus this neat lens at f/1.2-2.0?

 

What are some tips and tricks to using this lens?

My hypothesis is that Nikon calibrates the focus dot for accuracy at f/2.8 when a manual-focus lens is used. This represents a reasonable compromise in the face of focus shift—that is, the tendency of many lenses to focus slightly further back as aperture is stopped down.

 

Because of this, if you go by the focus dot at f/1.2, you'll be front-focused. The workaround is to turn the focus ring slightly to the right so that the dot is blinking alternately with the leftward-pointing triangle (on the right side of the dot). You can tune focus fairly precisely by judging the blink rate of the dot: if the dot is lit more often than the triangle, you'll be focused ever so slightly closer than if the triangle is lit more often than the dot.

 

Alternatively, don't use the focus lights at all when shooting at f/1.2, and instead use your eyes to judge whether the image on the focusing screen is in focus. I suppose a magnifying eyepiece can help there.

 

Last resort is to use Live View.

 

I have an easier time focusing my 50/1.1 Nokton on the M9- took both to the Marine Museum in Quantico.

 

These are wide-open with the 50/1.2 on my Df. It is spot-on.

 

Try using Liveview with Zoom and see of the focus on your AF spot is off.

I have a really neat manual focus Nikon 50mm f/1.2 Ai-S on a Nikon DF.

 

I have no problem focusing this (using Nikon's green arrow/dot focusing points) manually at f/3.5 or larger (which looks incredible). However, when I try to open this up at f/1.2 - 2.0 I miss 90% of the shots because they are out of focus even if the green dot focus point says it is in focus.

 

Other than swapping out the focusing screen to a split focusing system, is there a way to more reliable way to focus this neat lens at f/1.2-2.0?

 

What are some tips and tricks to using this lens?

 

 

This is pure supposition, but...

 

Have you entered the lens data in the non-CPU lens section on the camera and selected it? It might help.Are you using the center focus spot?

The Ai-S 50mm f/1.2 Nikkor, like many other wide aperture lenses, has a considerable amount of residual spherical aberration - hence the 'halo' effect wide open.

 

Spherical aberration gives a lens the peculiarity of having two planes of focus. A 'paraxial' focus and a minimum point-spread focus. As explained here.

 

What's generally wanted is the minimum point-spread, or minimum circle-of-confusion focus, but both the eye and camera AF systems are confused by this focus-spread, and tend to latch onto the paraxial focus, which has better contrast. The result being that the captured image is slightly out of focus.

 

The spread of focus closes toward the paraxial focus plane as the lens is stopped down, which is why spherical aberration is only an issue at open aperture, or nearly so.

 

Long story short: Neither your unaided eye nor the AF system can be relied upon to focus the lens accurately wide open. You absolutely need to use magnified Live View to get the best focus.

 

Alternatively, you can use the trick of watching for the first flicker of the AF confirmation dot when approaching focus from one direction. This could be from near-to-far or vice versa. It depends on the lens design. With a bit of trial and error and practise you can get to know how far into the green dot 'dead zone' you need to set the focus, and from which direction. Whatever method you choose, it's not a fast process.

Edited September 17, 2020 by rodeo_joe|1

As above, I never had any luck with my f/1.2 on my D200. Just couldn't get the plane of focus where it needed to be. Live view on the Z body works well, but it's a slow process and I consider the lens a novelty best used for situations that rarely occur.

Last resort is to use Live View

Surely, for this kind of 'still life' shooting, it's the only way to focus accurately?. Only LV is WYSIWYG.

 

How about focus peaking on suitably equipped bodies?

How about focus peaking on suitably equipped bodies?

Doesn't work with my a7Riv and 50mm f/1.2 Ai-S Nikkor wide open. I suspect the residual SA messes up any sort of AF detection.

Surely, for this kind of 'still life' shooting, it's the only way to focus accurately?. Only LV is WYSIWYG.

Agreed there.

LiveView should be the first resort with this lens (and its ilk) not the last!

Edited September 23, 2020 by rodeo_joe|1