• Ed Dozier

Using the Minolta Rokkor-PF 135mm f/2.8 on a Nikon Z9


What’s a more insane combination than an old Minolta manual focus Rokkor lens on the Nikon Z9? I can’t off-hand think of anything, so of course I had to try it.


I got a Fotasy MD-N/Z adapter that set me back a whopping $16 to try this combination out ;~). This adapter will let you mount MC or MD Rokkor lenses on a Nikon Z-mount. The Fotasy adapter has no electronics or optics; it’s basically a metal tube.


I have had some Minolta gear literally sitting on a shelf as knickknacks for several years. This stuff is there as a reminder of old adventures I had with it, before I switched to mainly Nikon gear. I never thought I’d shoot any more pictures with these lenses, since the death of the film era.


Did you know that Sony bought Minolta, and their original interchangeable lens cameras had Minolta (auto-focus) optics on them? Most people thought of Minolta lenses as second-best to Nikon, back in the day. You might think otherwise by the end of this article. Yes, Minolta made some lenses that were really second-rate, but there were also some gems.


Nikon just had to turn things upside down by inventing a ‘Z’ lens mount that will allow you to mount most anything on it, thanks to its large diameter and short flange distance. You just need to configure the “Non-CPU lens data” in their Setup menu to let the Z9 know what’s mounted on it. Here’s a link to various settings for getting the most out of any fully-manual lens used on a Z-mount.


Note that the camera EXIF data will record the lens focal length, the ISO and shutter speed, but the aperture will always be recorded as the same maximum aperture that you configured in the non-CPU lens setting.


I did a quick internet search and found a few adapters that let you mount the Minolta Rokkor MD or MC lenses onto a Nikon Z mount. They all allow infinity focus using the Minolta lenses. Needless to say, I couldn’t resist the temptation to try one of these adapters out.


Keep in mind, this Nikon Z9 lets me have IBIS (vibration reduction), aperture-priority, auto-exposure, and focus-peaking with any manual focus, non-CPU lens. It’s much easier to focus these old lenses using focus-peaking than it ever was with split-image or micro-prism screens in the film era.




MC Tele Rokkor-PF 135mm f/2.8 on Nikon Z9


I bought a used 135mm f/2.8 lens, which was manufactured around 1970. It has 6 elements in 5 groups, and has a minimum focus distance of 5 feet (I wish it focused nearer). It has the slip-out built-in lens shade, which I have always preferred. It has 55mm filter threads. The “MC” stands for “meter-coupled”. I wanted a ‘portrait’ lens that gives the subject a bit more breathing room, leading to pictures where the person looks more at ease.


This is an all-metal-exterior 135mm lens, and the optics have truly good bokeh. The focus ring rotates as smoothly as it did when it first came out of the factory. It only weighs 490 grams, which is surprising for an all-metal lens.


I “baby” my lenses; they don’t go out in the rain or get covered with sand or mud. I seriously doubt that these old Rokkors have any weather sealing, but if you treat them well, they should return the favor and treat you well, too. Since they don’t have any electronics in them, their lifetimes are almost guaranteed to far exceed lenses with focus motors and vibration reduction. Just don’t drop it.










Worst-case vignetting at f/2.8


Note how sharp the photo is edge-to-edge, even though the lens was used wide-open. If the vignetting looks excessive to you, it’s simple to fix it in an editor. I can see only slight lateral chromatic aberration, and I haven’t seen any distortion at all.




Frame edge detail from the shot above


Details like what’s shown above will readily show the dreaded purple fringes, if the lens has any tendencies to have lateral chromatic aberration. I don’t see any here at all.


When I use focus peaking and point the lens at flat lawn grass or textured carpeting, it’s easy to see if there is any field curvature. I don’t see any of that, either; the focus-peak speckles that I see are all parallel to the frame horizontal edge.




Lights at f/2.8 on the edge of the frame



If I hadn’t said anything about this lens’ origin, I doubt that anybody would guess that this photo wasn’t shot with a modern lens. Very, very nice bokeh.




Focus-peaking makes manual focus easy and accurate


You can see the little red edges around the parts that are in focus. It’s of course easier to use this same focus-peaking feature while looking through the viewfinder.




135mm f/2.8



Lens Measurements


I used the MTFMapper program to analyze shots from the Nikon Z9, taken in raw HighEfficiency format, converted to DNG format. I used the free Adobe DNG converter program to convert the HE shots (1/3 the size of regular compressed raw) into DNG. As of this date, none of my photo editors understand the HE format, but most of them understand the DNG format. The Zoner Photo Studio automatically invokes the conversion into DNG, so at least that editor works seamlessly with the HE format.




The full resolution target


The chart above is what I used to get the resolution, contrast, and lateral chromatic aberration measurements. The target is 40 inches tall by 55 inches wide. The chart also works well to get a visual evaluation of vignetting.





135mm f/2.8 Resolution


Notice how even the resolution is across the whole frame, with a peak of 40.9 lp/mm wide-open. This is plenty of resolution, even without stopping down. Lots of modern lenses aren’t this good.




Resolution numbers and vignetting sample, 135mm f/2.8


The shot above shows some sample resolution measurements overlaid onto the resolution chart photo. This also demonstrates the worst-case (f/2.8) vignetting. Nearly any photo editor can easily rid this vignetting, if you don’t want it.




MTF Contrast actual measurements, 135mm f/2.8


Notice how little astigmatism this lens has. Impressive. I always have to mention that most companies only publish 'theoretical' MTF contrast curves. My software produces these curves from actual measurements.





Lateral chromatic aberration, microns

Probably the weakest aspect of this lens is its lateral chromatic aberration. Fortunately, photo editors can (mostly) take care of this. When this lens was manufactured, your slides were stuck with this color fringing.




135mm f/4.0 Resolution

Stopping down one stop to f/4.0 gets a peak resolution of 44.5 lp/mm.




Resolution numbers and vignetting sample, 135mm f/4.0


Stopping down one stop really decreases vignetting.




135mm f/5.6 Resolution


Stopping down to f/5.6 gets a real jump in peak resolution, going to 50.4 lp/mm.




Resolution numbers and vignetting sample, 135mm f/5.6




135mm f/8.0 Resolution


Stopping down to f/8.0 reaches this lens’ highest resolution, going to 54.0 lp/mm. Image quality here is just excellent.


Stopping down further starts reducing resolution. The lens goes to f/22, but I'd recommend you don't go beyond f/16.




Resolution numbers and vignetting sample, 135mm f/8.0



Summary


I always liked this lens’ image quality, but only shooting with film never let the lens really show what it was capable of. Minolta (mostly) made better gear than people realized, and they had to design old lenses like this without the benefit of computers.


I can’t guarantee that this lens is representative of others using this design, but hopefully it will give you some idea of what kind of images these lenses are capable of producing. As a public service, I should mention that you should avoid their MD Tele Rokkor-X 300mm f/4.5 lens; I wish someone had warned me before I bought one many years ago.


If there’s a focal length that you know will only get used occasionally, a lens like this can be found for dirt cheap. Why on earth should a gem like this end up in the landfill?


It’s very liberating to know that you’re not constrained to just Nikon lenses when you are using a Z-mount camera. There will probably be many different third-party lens adapters that become available in the future.






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