Stupid damage to a Carl Zeiss 35/2.8 Distagon for Rollei QBM mount

forest bagger

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Hello folks,

I received a Carl Zeiss 35/2.8 Distagon for Rollei QBM mount for repair whose aperture did not close securely to smaller apertures (higher aperture values).




The oiliness of the aperture blades, which is often encountered, was not the cause!





Instead, the aperture blades were magnetized!

So I had to dismantle the entire aperture mechanism an demagnetize each single blade with a demagnetizing coil.




As I never had this before an the spring ring (the golden shimmering thing in this photo) had scratches in the surface I guess that a former repair man dismantled the aperture an magnetized the blades to replace them comfortably...
 

grain elevator

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Interesting, I've used a magnet to hold aperture blades in place and thought myself smart, that was a rangefinder lens though, so no quick action needed. I'll try to remember not to do that with SLR lenses.
 

Andreas Thaler

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Great!

Which tool did you use to demagnetize the aperture blades and how does it work?
 
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forest bagger

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grain elevator said:
Interesting, I've used a magnet to hold aperture blades in place and thought myself smart, that was a rangefinder lens though, so no quick action needed. I'll try to remember not to do that with SLR lenses.
Click to expand...
It's better to add some oil to the blades during mounting so that they stick together. After complete assembling the oil will be washed out by gasoline.
 
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forest bagger

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Andreas Thaler said:
Great!

Which tool did you use to demagnetize the aperture blades and how does it work?
Click to expand...
ELEKTRISCHER TONKOPF-ENTMAGNETISIERER, art.nr. 304856 from CONRAD ELECTRONIC SE

It works. The magnetism vanishes not completely but enough to bother no longer.
 

Sanug

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Yes, it works.

Question: Why did you deassemble the aperture blades? Why did you not use the demagnetizer with the blades assembled?
 
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forest bagger

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Sanug said:
Why did you deassemble the aperture blades? Why did you not use the demagnetizer with the blades assembled?
Click to expand...
At first I tried the demagnetizer in the assembled status, it worked not enough.
So I deassembled the aperture completely and demagnetized every single blade separately.
 

ic-racer

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I use the head demagnetizer for my audio tape deck when I need to demagnetize things, though I have never encountered magnetized shutter components. Thanks for sharing your experience.
 
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forest bagger

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Nov 9, 2023
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Since I had one of these lenses yesterday for repair (actually for assembly, since it arrived in two parts), here is an "explosion photo":





In order to access the straight line guide and the aperture mechanism from behind, you have to unscrew the large ring (the middle of the 5 at the bottom of the image) around the rear part of the lens.

This is difficult because it sits very tightly and there is no surface for pliers or similar tools to grip.
 
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