REPAIR: Pentax A 1.4/50mm cleaning (lots of fungus)

[stevemark]

There's not much information about servicing the Pentx A 1.4/50mm in the net. Here's a detailed step-by-step guide about dismantling and cleaning the Pentax A 1.4/50mm and all its six lens elements (five single lenses and one doublet).

Recently I got a rather nice looking Pentax A 1.4/50mm which was sold "as is", obviously with "some" fungus. The lens would - I assumed -fit my Pentax LX rather nicely. Up to now I had only the Pentax A 2/50mm and the Pentac A 2.8/50mm Macro normal lenses; and f1.4 normal would look nice, for sure!



When I got the lens it was obvious htat there was more than one surface contaminated with fungus, and in addition the focusing felt quite "dry" and uneven. The lens itself didn't look bad, and I assumed celaning it would be rather quick. I was wrong.

[stevemark]

PART I: REMOVING THE FRONT GROUP

Dismantling the lens starts with removing the focusing rubber:



You'll discover three "holes" in the focusing ring:


Pushing the three "buttons" insides theses holes (using a suitable tool) will free the front ring of the lens:



Front ring (nameplate) removed:


After extracting a TINY screw on the froont ring of the lens (not hte manplate ring which we alread heve removed!) we can unscrew and remove also the front ring of the lens:


This exposes the front group of the lens (be careful not to damage it since the front lens now is fully exposed!).
You'll find two tiny slots; one is shown here:


We can use a lens spanner to remove the front group:


Front group removed successfully:


Strong fungus growth on the galss surface facing the aperture:


Very nice fungus also INSIDE the front group ...!!


Well, the front group is sealed / glued - the tiny bright spot is a drop of glue:


There are no slots on the front ring of the front lens group; thus a friction tool was the only option to open the front group. Before trying it I immersed the front group for about an hour or so into acetone. While leaving it soaking, I went on working on the main lens.

[stevemark]

PART II: DISMANTLING THE LENS BARREL


Remove the five bayonet screws:


CAREFULLY remove the bayonet mount:


ATTENTION: there are two small parts which can be lost easily (arrow)!


The small golden spring (less than 1mm in diameter) an the silver metallic knob (less than 2mm) are part of the signal transferring mechanism for the "Auto Aperture [A]" setting:


Since we can't dismantle the lens any further from the back side, we have to go back toi the front side.
Remove these three screws:


Remove the corresponding plastic ring including the metal part which serves as a base for the screws:


Now the aperture mechanism can be removed:



Luckily it comes out as one part - nicely done by the Pentax engineers! It can be dsimantled further if necessary, but in my case everything was perfect and so I simply put it aside:


Now the foremost doublet of the rear lens group can be removed:



Next we can take off the aperture ring. I took me a while until I found out that i can be removed only if the aperture is set to f5.6!


Aperture ring removed:


Now we can take out these screws (three of the around the lens barrel):


Befor removing the black part we should mark it to allow proper re-assembling:


Part removed:


Now, finally, we have access to focusing threads! But before separating them we want to remove the rear set of two lenses:



Beautiful fungus also here, on all surfaces ...


Now extract these four screws and remove the two copper guides:


Unscrew the two parts of the focusing mechanism and mark the position weher they separate:


Finally there's another ring to unscrew - before doings so, measure the correct thickness (= position):


These are the parts of the Pentax A 1.4/50mm. Not yet dismantled: the optical front group and the rear lenses (yellow arrows). The red arrow shows the rear negative doublet which should not be separated, of course, but just cleaned properly.


Next step: dismantling and cleaning of the front and rear optical groups!

[stevemark]

DISMANTLIING AND CLEANING THE FRONT LENS GROUP

Dismantling the front as well as the rear group wasn't that easy. Both groups are secured with a simple ring that has no "attack points" to unscrew them.

Let's first work on the front group. The front ring on the front group obviously is glued in (see earlier image); therefore I decided straight away to immerse and soak the entire front group in acetone. After a few hours I took it out, and with the help of a friction tool I was able to remove the front ring pretty easily:


The first lens came out pretry easily as well; cleaning was easy as well. No trace of the fungus remained.


The second and third lens are still within their casing, and they have very nice fungus as well ...


Removing the small metal ring ...



...allows for removal of the next lens:


The thrid lens - still firmly in it casing - is affected as well:


Again cleaning was easy; no trace of the fungus would remain:


The re-assembled front group after cleaning:

[stevemark]

PART III: CLEANING THE REAR LENS GROUP

The rear lens group consists of four lenses in three groups [4/3]. The doublet directly behind the aperture comes out easily:


The last two lenses - two positive single lenses made of highly refractive lanthanum glass - are sealed in aas well. After soaking in acteone fr hours, unscrewing still was very difficult. I had to use "real gear" - not only a pincer, but a real pipe wrench! - to open this group. Of course one has to be VERY careful when using such tools on a lens ...!!



The two rear lenses are freed and now can be cleaned:


S

[stevemark]

I completely forgot to show the cleaned and re-lubed lens (here on a Pentax LX with motor drive):



S