Minolta MD 50/1.7 (III): Lens cleaning

[Andreas Thaler]

The - probably - first lens that came into my possession, along with a Minolta X-700. That was 1985.

In the meantime some dust has accumulated on the inner lenses.

This is supposed to disappear

As always, I try to find disassembly information before opening a lens.

This is intended to prevent - potentially fatal - surprises.

For example, the flight of the tiny ball - which causes the aperture to snap into place using a spring - into the wide space of the kitchen.

Mostly a goodbye forever

I found an excellent tutorial on how to completely disassemble this lens on high5cameras.com:

Minolta MD 50mm f1.7 / f2.0 Lens Repair Guide

Well briefed, I get to work.

The candidate, apart from the internal dust, is in excellent condition.

The sharp LED light shows the dust accumulation at the front and back.

With the rubber cylinders, unscrewing the decorative ring is easy.

Loosen the three screws that hold the filter ring.

After loosening another three screws, the lens sucker lifts the unit with two lenses out of the tube.

In the order

1. blow off
2. brush off
3. blow off
4. lens cleaning fluid on cloth
5. rework with a dry spot on the cloth

the dust on both lens surfaces is removed - as best as possible.

There is also some dust inside the tube, which the brush takes care of.

The unit with the lenses sits back in the tube.


But which three of the six holes in the tube are now responsible for attaching the lens unit?

I should have been more careful beforehand

Do all six screws even have the same thread diameter?

No, the three for the lens unit are 20 micrometers thicker as the caliper reveals.

As a test, I screw one of them into two holes next to each other.

Ah, it's easier here, harder there.

Wherever it's easier, I screw the unit tight using the thicker screws.

The filter ring then comes back into place.

The decorative ring is screwed in with the narrower end of the cylinder and fixed with the wider end - for more grip.

 

[Andreas Thaler]

The first stage of the cleaning tour has been completed.

We continue with the back of the lens.

The rear lens unit is screwed tightly.

A tight grip is used for better power transmission.

Of course, the second hand fixes the lens. Here it has to hold the iPhone camera

A tight grip because the three long screws sit deep and firmly in their holes.

A cover ring can now be removed and the lens sucker lifts the rear lens unit out of the tube.

Dust before ...

... and after cleaning.


There will never be a perfect result seen under LED light, but that doesn't matter at all in practice.

The main thing is that the amount of dust has become significantly smaller.

The cleaned lens unit is screwed back on.

Since all of the previous screws are in plastic, I don't tighten too much.

The lenses are now much clearer.

Mission accomplished


Conclusion

• This was not a particularly difficult exercise, but it still requires full attention, as shown by the uncertainty surrounding the selection of drill holes.
• The amount of plastic inside - all screws are in plastic parts - surprised me. Nevertheless, this 50 is very solid.
• I mainly worked with the short cross recess screwdrivers (JIS standard). I can use them more safely at close range than the longer versions, which in turn enable higher torque.
• Photographing actual dust under LED light proves difficult. Depending on the passage of light, more or less dust pops up. In any case, the dust infestation is now significantly less than before.

Two more photos of the cleaned lens shot under non-directional light:

+++

I would like to apologize for the partly poor image quality.

All information provided without guarantee and use at your own risk.

 

[Flighter]

Bravo! A great step by step guide.
Looking good, especially the last picture.

A tip I've been given when replacing screws into plastic parts is to initially the screw anticlockwise (with little pressure applied) in order the feel where the thread in the plastic starts and then the screw can be tightened up as normal. This avoids the risk of cutting another thread in the plastic and eventually, if the screws are frequently removed and replaced, of stripping the threads in the plastic.

 

[Andreas Thaler]

Bravo! A great step by step guide.
Looking good, especially the last picture.

A tip I've been given when replacing screws into plastic parts is to initially the screw anticlockwise (with little pressure applied) in order the feel where the thread in the plastic starts and then the screw can be tightened up as normal. This avoids the risk of cutting another thread in the plastic and eventually, if the screws are frequently removed and replaced, of stripping the threads in the plastic.

Thank you, also for that hint!

I can add that the pitch of the thread on screws for plastic is steeper than on screws for metal. I'll add a photo soon to show.

 

[xkaes]

For example, the flight of the tiny ball - which causes the aperture to snap into place using a spring - into the wide space of the kitchen.

It's nice to know that I'm not the only one that this happens too!

 

[Andreas Thaler]

It's nice to know that I'm not the only one that this happens too!

My goodness, how many times have I crawled around on the floor of our kitchen with a magnet in my hand. But since I got replacement balls in all sizes from microtools, I've saved myself that

 

[forest bagger]

Hello Andreas!

We continue with the back of the lens.

View attachment 354560

There are three noses with very small holes near to the big holes for the three screws.

I think these noses are used to fine adjust the position of the rear lens group before the lens group is firmly monted.

So you should test the freshly cleaned lens, if it performs crisply sharp again!

 

[Andreas Thaler]

Hello Andreas!

There are three noses with very small holes near to the big holes for the three screws.

I think these noses are used to fine adjust the position of the rear lens group before the lens group is firmly monted.

So you should test the freshly cleaned lens, if it performs crisply sharp again!

Thanks, that's interesting.

I have just looked at the photos again.

The three small noses (lugs) on the lens frame have holes that are not continuous. These holes point towards the rear part of the lens. There are no holes on the opposite side, i.e. underneath around the aperture register.

There were no screws there either, and since I'm the original owner, the lens hasn't been opened before. So I don't see any possibility of fine-tuning.

After assembling it, I tested the lens on the camera and couldn't see any irregularities, at least in the viewfinder.

What else could the noses and half-drilled holes be for?

 

[Helge]

Absolutely fantastic. Really useful and interesting.
Do the 24mm 2.8 next. I have a specimen that has what looks like some strands of three day stubble inside it. Something I’ve seen in on other Minolta lenses. Dried up lubricant from the focus helical, ending up in between the elements perhaps?

Any theory on how so much dust gets into the lens? It seems hard to believe that it’s sucked in. Static build up perhaps?

I notice you have a bit dry hands in the winter like me. This is absolutely worth the money and improves your grip in fine motor work a lot.
Better than any other hand salve. Absorbs quickly and works.

 

[Andreas Thaler]

Absolutely fantastic. Really useful and interesting.

Thank you

Do the 28mm 2.8 next. I have a specimen that has what looks like some strands of three day stubble inside it. Something I’ve seen in on other Minolta lenses. Dried up lubricant from the focus helical, ending up in between the elements perhaps?

Could you perhaps post a picture for investigation?

Any theory on how so much dust gets into the lens? It seems hard to believe that it’s sucked in. Static build up perhaps?

I'm also at a loss.

I actually almost never used the lens because I soon replaced it with a small zoom. It was covered when stored. It's the kit lens that came with my X-700 back then. I bought everything new, financed by doing task work in the factory as a student

I notice you have a bit dry hands in the winter like me. This is absolutely worth the money and improves your grip in fine motor work a lot.
Better than any other hand salve. Absorbs quickly and works.

View attachment 354622

Thanks, excellent!

I can use this now that I only work with nitrile gloves

 

[forest bagger]

... the lens hasn't been opened before.
After assembling it, I tested the lens on the camera and couldn't see any irregularities, at least in the viewfinder.

In the viewfinder it is almost impossible to see any irregularities caused by a slightly decentered lens.

Can you move the rear lens a little bit from side to side when the three screws are not firmly fixed? If not, there ist no fine adjusting possibility.

 

[Andreas Thaler]

Can you move the rear lens a little bit from side to side when the three screws are not firmly fixed? If not, there ist no fine adjusting possibility.

As far as I remember correctly, no movement is possible.