LENS REPAIR GUIDE BY MEL PARKER JONES
Minolta MC ROKKOR 58mm f1.4
A step by step guide to repairing the mighty Minolta Rokkor 58mm f1.4
This guide can also be used for many other short focal length MC series lenses such as the
55mm f1.7. Most short focal length Rokkors share a very similar construction and while
there may be minor differences the essentials will be almost identical.
This is NOT true of long focal length and zoom Rokkor lenses which will be very different in
design and construction.
The guide covers the MCII series but MCI series will be identical.
This guide will NOT be appropriate for MCX Series, MD Series or the earlier Auto Rokkor
models which all employ very different construction.
Copyright 2020 Astro-Baby ,
Free to use, copy and distribute so long as no charge is made for use,
distribution or access and authorship is freely acknowledged.
NOTES BEFORE YOU START
Start by putting a rear lens cap on while
you work on the front part of the lens.
The quality of any repair is down to your
skills, your tools, patience and most of
all mindfulness.
Good servicing is taking your time, there
are no prizes for the fastest lens strip
down and rebuild.
STEP 1
Remove the lens beauty ring. This can
be done with a lens spanner but a
rubber cup is a better solution. A lens
spanner can easily mar the finish on the
beauty ring.
The Minolta Rokkor 58mm f1.4 is a relatively easy lens to work on but please bear in mind
that this is a guide, you may well face challenges inside the lens that you will need to work
out. These can include stripped screws, deformed parts etc.
When working on one side of the lens (eg the front) always be mindful about what’s
happening at the other side (eg the back). I always keep caps on as much as possible to
prevent any accidents. The classic mistake is for people to press on the lens while it is on a
workbench and break things on the downside of the lens like the aperture lever.
There is no such thing as luck in repairing optical equipment, if you do it right, using skill and
patience you will be rewarded with a perfectly operating lens. A rushed or bodged job will
result in the lens being devalued, unpleasant to use and possibly unusable so…..take your
time, get the right tools and materials, don’t take shortcuts or advice from people who
know less than you.
There are no prizes for fastest or almost working in the world of lens repair so read the
guide from end to end before starting to familiarise yourself with the process.
With the beauty ring removed all of the
essential screws and fittings for the
front part of the lens are exposed.
STEP 2
Start by removing the front optical
element group. You will see there are
two sets of lens spanner cut outs. You
need only the outer pair.
Apply the lens spanner and gently but
firmly turn the lens while keeping
downward pressure on the spanner.
The front optical group after being
unscrewed can be simply lifted out of
the lens body.
Store this somewhere safely. I usually
store lens groups in a Tupperware box
lined with lint free cloth pending
cleaning and reassembly.
You are advised not to disassemble this
group but cleaning will be discussed
later.
With the front optical group removed
the aperture mechanism is now
exposed…….
Its safest at this point to open the
aperture to its widest. This will
minimise risk of damage to the very
fragile aperture blades as you move
forward in the disassembly.
STEP 3
Using a JIS screwdriver remove the three
screws that retain the filter ring…..
…and simply lift the filter ring away.
Make sure the screws are stored safely
and not mixed up with other screws. I
normally allocate small dishes for the
various screws and fastenings to avoid
confusion later.
STEP 4
You now need to remove the diaphragm
assembly. This is retained by 4 screws
around its edge.
One of them is highlighted in the
picture….
Using a JIS screwdriver remove the four
screws around the aperture
mechanism…..
….and remove the diaphragm assembly
carefully. The rear optical group is still
attached to this so extract this with
great care so that the rear optics are not
damaged.
Here is the diaphragm assembly rear
view after removal. You can see that
the rear optical group is still attached. It
is far easier usually to remove this group
with the diaphragm removed.
Take great care of the diaphragm
assembly, it is fragile and easily
damaged by rough handling.
Take note of the fact that the assembly
has a flat edge on one side. You will see
why later.
STEP 5
With care unscrew the rear optical
group. Be careful here as the diaphragm
assembly has a number of small parts at
the rear and the pins and springs can be
easily damaged.
Remember to stay mindful, keep
focused, and THINK before you act.
Store the optical groups somewhere
safe while you move forward with
disassembly.
Here are the two optical groups from
this lens being stored in a small
Tupperware box line with lint free cloth.
STEP 6
Check the diaphragm assembly for
correct function and see whether there
is oil contamination.
If the oil contamination is light I usually
spray the diaphragm out with a Freon
free cleaning solvent and then let it bath
in Isoprop Alcohol for around an hour
before leaving it to dry thoroughly at
room temperature.
If the unit is heavily contaminated it will
require stripping down completely.
Diaphragm strip down and rebuild is not
usually required and this guide will not
cover this aspect.
STEP 7
Now its time strip the focus mechanism
for cleaning and lubrication.
Set the lens focus to infinity.
Its assumed that the lens focused
correctly prior to stripping down but if
not don’t worry it will be corrected later.
Start by removing the three screws
around the edge of the focus barrel.
These are on top of the brass colored
ring.
Take care to extract each screw after
removal and be careful – each of these
screws has a tiny washer – DO NOT LOSE
THEM.
Once removed, store them safely.
With all three screws removed the focus
barrel will simply slip off from the lens
body….this reveals the two focusing
helicoils.
These go by different names but to keep
life simple the guide will refer to the
brass colored one as the outer helicoil
and the silver colored (inside the brass
one) one as the inner helicoil.
Measure the distances between the
inner helicoil to the brass helicoil
(normally on an MC lens the inner
helicoil will be almost flush with the
brass outer helicoil.
Measure also the gap between the brass
helicoil and the lens base. Normally I
use a collection of fine screwdrivers to
assess distance. In this case a 1mm
driver is being used and it is an exact fit.
Make a note of these measurements.
STEP 8
Now remove the lens mount assembly
from the rear of the lens body.
Start by removing just a single screw. If
the screw is short then replace it. If it is
long remove it.
DO NOT REMOVE THE SHORT SCREWS
Here is a picture to give you an idea of
scale of the short and long screws.
These alternate around the lens mount
plate. You only need to remove the 4
long screws for servicing of the lens.
Removing the short screws will release
parts of the lens that are difficult to
reassemble and generally there is no
need to remove these parts.
With the four screws removed, as
before store them safely and then
simply pull the lens mount assembly
from the body of the lens.
Take care also at this point NOT to
remove the aperture ring. I usually tape
the aperture ring to the body prior to
this step to make sure it does not come
away with the lens mount due to stuck
grease.
STEP 9
Cup the rear of the lens in your hand,
preferably inside a Tupperware box or
clear bag and gently pull the aperture
ring free.
Inside the ring there is a tiny spring and
ball bearing and these can easily fly out
and be lost.
Sometimes the bearing will stay with the
lens, sometimes it will fall into your
hand. Sometimes it will simply vanish –
take this step easy. If you don’t see the
ball bearing examine your hands
carefully. Its so small it may be stuck to
your hand.
This is why I generally do this inside a
large clean bucket or Tupperware box.
It minimises the risk of a loss.
The previous picture and this one give
an idea of size – the bearing is most
normally around 1.2mm.
In the previous picture the bearing is
sitting on top of a small spring. This
bearing and spring provide the click
stops.
Store the bearing somewhere safe.
Place some low tack tape over the hole
with the small spring to prevent loss or
remove the spring entirely.
A small needle, needle nosed tweezers
or a cocktail stick can be used to extract
it. Store this safely with the bearing.
The spring is very tiny (barely larger than
the index numbers on the lens), take
care when handling it as it is prone to
flying off and getting lost.
STEP 10
Remove the three screws from the
helicoil key/lock tab.
Be careful here as these are sometimes
lacquered in place. If they don’t turn
out easily apply some heat or isoprop
alcohol.
Its very easy to strip the heads on these
so take care.
Remove the helicoil key/lock tab.
Unscrew the helicoils from the lens
body.
Its good practice to count the turns
before the parts separate and mark the
separation point on the two parts.
Its not necessary for the 58mm f1.4 MC
but it is good practice – not all lenses are
kind to technicians.
L-R in picture – lens body, outer helicoil,
inner helicoil.
Note: The inner helicoil has screw holes
in its top part – this faces the front of
the lens when assembled.
This completes the strip down of the lens.
We now have to consider cleaning the components and reassembly.
For cleaning you will need a soft toothbrush, cotton wool balls and Isopropyl Alcohol (IPA)
and a lot of patience. I generally clean down with hot soapy water first and then soak the
helicoils in IPA for a few hours before wiping down with cotton wool. The threads on the
helicoils are extremely fine and the smallest piece of grit or dried grease will cause
problems later on. Usually these are chased out with a fine needle before cleaning again.
My own view on cleaning is to get the parts absolutely spotless prior to reassembly to
give the lens the longest life before any further servicing is needed.
Normally when I rebuild a lens I will strip and clean EVERYTHING. The lens mount
assembly can be flushed with IPA, all of the barrel components such as the aperture
control ring, filter ring and focus barrel will be thoroughly cleaned. Index marks with their
numbers can be scrubbed with a soft toothbrush to remove dirt and grime.
OPTICS CLEANING
The Minolta MC series can show haze caused by oil vapour on the lens group inner
surfaces. These are the optical surfaces that face inside the lens in each of the two
optical groups. These can be cleaned with a mild IPA solution and a lint free soft cloth.
You need to exercise extreme care here and do not apply pressure to the glass. Apply a
mild IPA solution to the cloth just so the cloth is damp and then apply lightly. Use a
puffer brush to blow off any moisture and then use a clean cloth to polish out any
evaporation marks.
CAUTION
You are advised NOT to remove the lenses from within each group. Minolta used a very
soft coating formula in almost all of the MC series lenses and this can be damaged by
even very mild cleaning and careful handling.
I normally clean the optics just prior to their reassembly into the lens and make sure the
lens interior is blown clean with a puffer bulb. You will always find some dust is present
on reassembly – do not worry – they were no different when they came from the factory.
After cleaning the helicoils should be
lightly greased using a suitable lubricant.
I prefer Helimax XP for most Minolta
lenses. This is applied thinly using a fine
sable brush. On a Minolta MC series the
lens is semi self lubricating thanks to the
material used in construction of brass to
aluminium so the lubricant needs to be
quite thin and very evenly spread.
Notes on lubrication - The first time you so this you will need to work by trial and error to
get the right feel.
Too much lubricant will result in the focus being stiff, too little and it will grind or be too
light. You can test the ‘feel’ while the helicoils are assembled but it will be hard to assess
without practice as to what the lens will feel like with its focus barrel mounted.
STEP 11
On reassembly the object is to get the
helicoils spacing for focus the same as
you measured at the end of STEP 7 and
with the lock tab recess aligned to the
threaded holes for the lock tab. You
don’t have to be super precise but its
best to get it as close as possible. You
may need to unscrew the helicoils a few
times and try at different entry points to
the threads to achieve this.
Replace the focus lock tab. Take care
not to overtighten the screws.
After replacing check that the helicoils
will rotate correctly. The lock tab, if not
centred can cause the focus to jam or be
stiff. I normally apply a very thin smear
of Helimax XP to the sides of the recess.
STEP 12
Do a trial run of fitting the aperture ring
to the rear of the lens. Some MCs will
be fussy about what position the ring
needs to go back on (eg will only easily
fit at the f5.6 position) Do a dry run if
needs be BEFORE replacing the small
ball bearing.
The trick to get the bearing back into
position is to replace the spring and
then apply a small dab of
lubricant/grease to the top of the spring.
Apply the bearing to the grease to hold
it in place.
I normally position the bearing by using
a cocktail stick with a small dab of
grease on its end to retain the bearing….
…keep the lens body in position while
you keep an eye on the bearing and the
apply the aperture ring at a slight angle
to trap the bearing in place and then
ease the aperture ring down over the
rest of the lens body.
This is why you do a dry run earlier at
the start of STEP 12 to make sure the
ring will fit easily as some MC lenses will
be awkward to fit the aperture ring at
some positions.
While making sure the aperture ring
does not slip off apply the lens mount to
the rear of the lens body making sure
the aperture actuation lever is at the
base of the lens and on the opposite
side of the lens to the aperture index
mark.
You can see in the picture the aperture
index mark is on the opposite side to the
aperture actuation lever.
Replace the four long screws into the
lens mount ring. Do not overtighten
these for now.
This is in case anything is wrong and
requires a quick strip later.
Just tight enough is good enough for
now.
STEP 13
In order to replace the diaphragm
mechanism you need to be aware of
some elements of assembly.
Th diaphragm barrel has a flat side as
shown in the picture. This has to locate
against the lens body where the focus
lock tab sits…..
….here is the focus lock tab and the flat
part of the diaphragm barrel needs to be
aligned with this PLUS…..
The diaphragm actuating lever shown
needs to locate into the aperture control
ring slot on the lens body……
….The aperture control locating slot is
shown here. This is where the
Diaphragm body lever needs to mate to.
It seems tricky but in fact its quite easy.
Here’s how to do it…
First set the aperture control ring to
f2…..and by using the diaphragm barrel
lever at its rear open the diaphragm to
its widest aperture.
Place the diaphragm barrel into the lens
making sure the flat side is aligned with
the focus lock tab.
Look through the rear of the lens body
(this is why you leave the rear lens
element out during reassembly until this
step)…..
..and maneuverer the diaphragm and
the aperture ring until the diaphragm
lever is located into the aperture control
ring slot.
This seems hard at first but you will see
it is actually quite easy in practice.
Once diaphragm is installed hold it
gently in place and rotate it slightly so
that the screw holes align.
Cap the rear of the lens to protect the
aperture lever and replace the screws
that retain the diaphragm barrel to the
lens body. Do not overtighten as these
can shear off under too much torque.
Once secured check that the diaphragm
is behaving normally by selecting f16
and operating the aperture actuating
lever. The aperture should stop down
and reopen quite normally. Check also
operation at f1.4
STEP 14
Replace the rear optical group…..
I would normally clean the group before
reinsertion and blow the inner surface
clean.
….and secure the group with a lens
spanner.
Replace the front optical group…..
These would be cleaned at this point
and the inner surface blown clean.
Prior to securing the front lens it’s a
good idea to run a quick torch test
before the lens is fully secured down.
This may catch any pieces of dust or lint
prior to final assembly.
…and secure with a lens spanner.
STEP 15
Attach the lens to a known good camera
look through the viewfinder and use the
brass inner helicoil to bring the lens to
infinity focus.
I normally aim at a pair of radio towers
around 8 miles away and use a camera
with a split field focus.
Once you are happy that the lens is
focusing correctly set the lens at infinity
and then very carefully replace the focus
barrel making sure the barrel indicates
infinity against its index mark.
Replace the focus barrel retainer screws
with their washers and lightly tighten.
Recheck focus and once happy tighten
down – do not overtighten as these
screws will shear easily.
Replace the filter ring.
Replace the beauty ring.
Check lens for all functions and do a
final tighten on the mount ring if you left
this loosely dogged down at the end of
STEP 12
Fully check lens focuses correctly and
that all f stops are working correctly.
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