MS-Optical Sonnetar 50mm rangefinder not coupling to infinity

[moomooranch]

Hi friends,

I've recently purchased a used Sonnetar 50mm, but it would not couple with my rangefinder properly - setting the lens to infinity, the rangefinder patch would instead appear to be focused to something 4-5m away.

I know my rangefinder is calibrated fine, because my five other M lenses work as expected.

Inspecting the rear of the lens, it looks like there is a shim that is screwed into the helicoid, which makes contact with the RF roller.

Image indicating the screw-in shim (the ring with rectangular notches every 90 degrees):

The shim was loose when I got the lens. Tightening it made the coupling error even worse (lens at infinity corresponded to the RF coupling to something at 3-4m away). I was able to loosen it to the right spot to achieve infinity focus in the RF patch and also infinity focus on the lens.

I was wondering if tuning the RF coupling by loosening this shim was the intended design? It seems a bit precarious, as this ring can freely turn in this position. Have other Sonnetar owners run into the same issue?

 

[Huss]

That is the coma adjusting ring, which adjust coma and focal point. I'm sure there are online resources that should be able to explain its use.

 

[moomooranch]

That is the coma adjusting ring, which adjust coma and focal point. I'm sure there are online resources that should be able to explain its use.

The coma adjustment ring is the ring around the rear element (the ring with the red dot painted on it). I adjusted the coma ring when I first observed that the RF coupling was off, but since the coma adjuster doesn't touch the RF roller, it has no effect on the RF calibration.

Image better showing where the coma adjustment ring is:

 

[uhoh7]

I would send this to MS Optical, who I'd bet would repair it at no cost except shipping. It sounds like there may have been some "history" in use with it's original owner. My new one is fine, and I have not heard this problem from other owners.

 

[moomooranch]

I would send this to MS Optical, who I'd bet would repair it at no cost except shipping. It sounds like there may have been some "history" in use with it's original owner. My new one is fine, and I have not heard this problem from other owners.

Interesting, thanks for the insights. I'll check with Japan Exposures to see if they can help with triaging with MS Optical regarding servicing this lens.

 

[Pioneer]

I did have some problems early on with my Sonnetar when the focus coupling loosened. As a result, as you have seen, the focus distance will will change at infinity.

At the time I wasn't interested in fiddling with it so I sent it back to MS Optical through Japan Exposures for repair. I have had no trouble since.

 

[Dante_Stella]

Are your focusing ring set screws loose? The slotted ring you are highlighting does not turn on mine. It may also have been Loc-tited on original assembly.

Dante

 

[Huss]

The coma adjustment ring is the ring around the rear element (the ring with the red dot painted on it). I adjusted the coma ring when I first observed that the RF coupling was off, but since the coma adjuster doesn't touch the RF roller, it has no effect on the RF calibration.

Image better showing where the coma adjustment ring is:

Sorry for the mis-information, glad u and others corrected.

 

[hap]

Ms Optical

Ms Optical

I have this lens......the helicoid willl move a lot when you turn the focus ring.

The coma adjustment, if it is not turned all the way in first, will absolutely throw your infinity focus off.. It happened to me and it was embarrasing. Turn it all the way in and then the adjustment is just a partial turn to align the red 4m mark to the small white dot.

it should focus well at infinity. If you can, put a gg on your rail and watch it focus, noting the RF and the lens markings.

 

[hap]

Ms Optical

Ms Optical

That retaining ring does not turn on my lens, either.

 

[moomooranch]

Are your focusing ring set screws loose? The slotted ring you are highlighting does not turn on mine. It may also have been Loc-tited on original assembly.

Dante

The focusing ring seems fine, because the optical group is properly "butting" against the mount when the lens is set to the infinity mark.

Besides the slotted ring, there doesn't seem to be anything else that changes the relative distance of the RF coupling point to the base of the lens mount. The slotted ring itself doesn't have any drill holes for grub screws, which leads me to believe that the original calibration was indeed probably set using Loctite.

 

[moomooranch]

That retaining ring does not turn on my lens, either.

Thanks for the info! It looks like this is indeed an anomaly, and the lens requires service.

 

[moomooranch]

I did have some problems early on with my Sonnetar when the focus coupling loosened. As a result, as you have seen, the focus distance will will change at infinity.

At the time I wasn't interested in fiddling with it so I sent it back to MS Optical through Japan Exposures for repair. I have had no trouble since.

Hmm, interesting; it's not an isolated problem then. I wonder how this ring was set. This makes me a bit concerned about the sturdiness of the construction - I think I'll return it to the seller and purchase either a new Sonnetar for easier warranty / service requests or a C-Sonnar instead.