Element misalignment after DIY CLA ?

Keysersoze27 · Expire: 2012-12-24

I see a lot of persons disassembling their lenses . I've done that myself many times.

My question is what negative effects might arise whet you open a lens group apart . I've never done this but I might now since I bought all the appropriate tools.

You see these lenses were put together by trained assemblers. A group is usually contained in a metal housing and screwed together with hardware that was designed to hold the lens elements.Groups might be assembled then aligned on a fixture optically. Actually people are sending expensive old lenses to Pro service companies or even the len's own service Company to recalibrate them after a fall or typical age related misalignment .

What are the possibilities to have loss of resolution/increased CA/ loss of contrast that I've read in the net in similar situations ?

I intend to remove some dust from the 2nd rear element of my Macro-Elmarit R 60 . I have read negative experience about DIY CLA on Leica R lenses because of assembly difficulties so any advice will be welcome .

Orio · Expire: 2012-12-04

I do not have first hand experience, but I can tell you for sure that in the assembly lines of companies the optical groups are put together using precision instruments for measuring distances and alignment.
So simple logic would say that by reassembling manually, the risk of doing a coarse work exists. Whether that would also cause visible consequences remains to be seen (I suspect that unless doing a really poor job, a reassembling small imprecision would cause a loss of quality that only instruments would record, not a human in a typical average viewing condition).

ZoneV · Expire: 2011-12-02

I opend some older lens assemblies - most time to clean lenses from fungus.
At the lenses I opend this far (no Leica R) there where clear positions - mechanical stops - where one side of the lens has to sit on. On the other side a screw ring hold the lens in place.
The diameter of the lenses is very close to the diameter of the barrel - sometimes I had problems to get the lens out of them - because they fit that exact.
So there is not much room for missaligment.

The manufacturer has the aligment work in the production process, they have to center the lenses - that is to grind them to fit in the barrels in that manner, that the optical center is in the center of the barrel. You could not adjust that - but neither you could deadjust that.

There are some rare lenses that have some centring adjustment screws - with those you could alter the centring. If you don�t open the screws, and don�t disassemble this lenses I see no problems. But you have to know which screws that are. I think Leica has some lenses with that!

Lenses with internal foccusing or floating elements could cause more problems. Or zoom lenses.

A common missaligment is to assemble lenses with twisted front and backside. To minimize this risk it is good to use some marker on the glas.

I try to make some photos before I open a lens, and afterwards I compare if I see problems. Best would be with the same setup - but I do not have room enough to do that normaly.

Apart from the lens group disassemly the focus heliocid is often a real problem.

Up to now I am happy with my repair results.

Keysersoze27 · Expire: 2012-12-24

Thanks for the replies guys!!!

I will skip the Leica's CLA for the time been Laughing

aliasant · Joined: 17 Feb 2010 Posts: 39 Location: Stockholm, Sweden

As ZoneV said; you cant really misalign most lenses since they sit in a fixed tube. I had one Meyer that had the small screws that adjusts the back lens and I screwed that one up, but thats 1 lens out of 30 or so.

Helicoids are often the biggest problem.
If you are about to unscrew 1 thing from another always do it really slow with a steady but gently drag so that when it comes of the thread you still hold the two parts together. now MARK somehow exactly were they parted so that you can screw them back together the exact same way.

Often I can see small faint scratch marks from someone elses assembly and if you see those use them Smile

On the other hand.... You shouldnt really disassemble a lens just because there is some dust in it.
Dust will never affect the image you get and you are much more likely to end up with a lot more dust then you had before you opened the lens anyways.

I have personally been thinking about building some kind of dust free box for the reassembly process but havnt got around that yet.

Keysersoze27 · Expire: 2012-12-24

goombles · Joined: 08 Apr 2010 Posts: 136 Location: UK

aliasant · Joined: 17 Feb 2010 Posts: 39 Location: Stockholm, Sweden

Keysersoze27 · Expire: 2012-12-24

Guys,

What do you use -when you open the inner parts- to protect the elements from any spanner wretch's accidental scratch ?

cyclical rubber? paper? tissue ?