Destructive removal of a stuck lens filter; testing for radioactivity

[Andreas Thaler]

A Vivitar skylight filter was stuck on a Rikenon 55/2.8 lens and wouldn’t budge even with the lens filter wrench.

Since the filter was already damaged and had a dent, I didn’t want to waste time trying WD-40 to loosen it.

Besides, this presented an opportunity to try out a technique that Thomas Tomosy describes in one of his two books on camera repair1.

To do this, the glass is removed, the filter ring is cut in, and then, using combination pliers, it is pried out of the filter thread on the lens with a twisting motion.

This destroys the filter, so it’s a last resort when nothing else works.

Since the dent made it impossible to remove the glass, I carefully tapped the glass with a small hammer and removed the broken glass pieces.

This created glass dust that fell onto the work mat.

All went well

the job was done without damaging the lens.

Now I started worrying about the glass dust

After all, there are lenses that contain thorium and emit alpha radiation.

As long as the glass isn’t damaged and no pieces of it enter the body, it’s harmless. Alpha radiation can be blocked by as little as a sheet of paper. According to my research, the levels of beta and gamma radiation are not cause for concern.

Anyway in fact



I found a video where someone detected low levels of radiation from skylight filters.

This worried me, so I got a radiation meter, researched the topic, and concluded that the glass shards from my Vivitar skylight filter did not exceed background radiation levels.

Meaning they are not radioactive (both around 20 counts per minute—cpm).

For comparison, I measured a piece of uranium glass, which emits a significant amount of radiation at 86 cpm but it's not dangerous.

An interesting topic. Perhaps I’ll find another lens with thorium glass in my lens collection.

When doing this kind of work, you should take every precaution to protect yourself.

Small pieces of glass can fly off unpredictably.

So face protection, safety goggles and hearing protection are a must for me. As they always are when working with the Dremel.

A respirator filters out particles.

---

1 Camera Maintenance & Repair, Book 1: Fundamental Techniques: A Comprehensive, Fully Illustrated Guide

+++

A word of caution

Please keep in mind that you’ll be using highly flammable solvents for service work, and their fumes are harmful to your health. Soldering also produces fumes that should not be inhaled. Dangerous high voltages can be present when handling electronics, especially in conjunction with electronic flash units and mains. Therefore, familiarize yourself with the safety regulations beforehand and ensure your safety. Depending on the activity, protective gear may be advisable.

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

 

[MattKing]

I'm tempted to share this with my camera repair friend - to see if the sight of the camera and the hammer causes him to shudder .
As I understand it, Thomas Tomosy and him were friends, but mostly because they were in the same group of camera collectors.

 

[Andreas Thaler]

I'm tempted to share this with my camera repair friend - to see if the sight of the camera and the hammer causes him to shudder .

Please give him my best regards. In Austria, we solve everything with a hammer

As I understand it, Thomas Tomosy and him were friends, but mostly because they were in the same group of camera collectors.

Thomas, one of our great masters.

 

[koraks]

When breaking glass, you could tape it first so you get less splinters flying about.
Looks like you nicked the filter thread on the lens with the angle grinder...

 

[Andreas Thaler]

Looks like you nicked the filter thread on the lens with the angle grinder...

Yes, a tiny bit but a bit

 

[koraks]

Not a very unique lens, so I imagine you're not worried about it.
It's funny how incredibly stuck those filters can get, isn't it?

 

[Chuck1]

This also works for pipe fittings

 

[Andreas Thaler]

Not a very unique lens, so I imagine you're not worried about it.

Every item on the table gets 100 percent respect. If I damage the front lens while doing this, I should put the tool away.

But it’s also fun to destroy something once in a while. In this case, the filter

 

[koraks]

Yeah, definitely. Although when it comes to destroying things, I find it is especially rewarding if you can put some serious force into it!

 

[Petrochemist]

Why would the filter be radioactive? Filters have flat sides so their refractive index is not critical (o need for thorium glass)
Exposure to alpha beta &/or gamma radiation does not make things radioactive, - it takes neutron bombardment to do that.

 

[Andreas Thaler]

Why would the filter be radioactive?

Yeah, I was wondering that too.

But while doing some research, I came across this video, which apparently shows evidence of low-level radioactivity.

 

[Dan Daniel]

Dust mask also good if grinding metal and/or glass. Especially glass.

I've taken 1/4 of the diameter off of a filter thread on an Olympus lens after the threads were smashed down. Remember, if you have only maybe 15 degrees of the mount at 120 degree spacing, the filter would still go on and be secure.

 

[mshchem]

In Austria, we solve everything with a hammer

In the US we would have used a much bigger hammer

 

[Petrochemist]

Yeah, I was wondering that too.

But while doing some research, I came across this video, which apparently shows evidence of low-level radioactivity.

That's almost just certainly background radiation, though surface contamination is possible.

 

[MattKing]

I had coffee with my friend this afternoon, and mentioned this thread.
He said that he has and has used more than one hammer.

 

[fgorga]

Many years go, while in high school and college, I worked at a service station owned by a fellow named Henry.

Henry's first rule of auto mechanics was if a first you don't succeed, get a bigger hammer! His second rule was if the bigger hammer doesn't work break out the acetylene torch!!!

I learned from the best but I am not sure how these rules apply to camera repair!

 

[reddesert]

No sane designer would ever use something like a thorium doped glass in a filter. And thorium glass went out of common use in the 60s or so. Designers use a variety of glasses for lenses because they need specific values of index of refraction and dispersion to balance the different curved elements in the lens. But a filter is flat (no optical power) and you don't need to worry about the dispersive properties, you just get whatever you get.

It might be something like plain crown glass (like BK7), which is about the least expensive optical glass that can be bought. (I suppose a filter could be even cheaper float glass, but I don't know if that is flat enough.) If you buy a typical simple convex or concave lens from Edmund, Thor Optics, etc, it will be crown glass like N-BK7, or the equivalent from another glass supplier.

 

[Patrick Robert James]

Zero reason to Dremel the ring. Just tap out the glass then take a pair of pliers (regular not needlenose) and twist. It will come right off.

 

[Andreas Thaler]

Zero reason to Dremel the ring. Just tap out the glass then take a pair of pliers (regular not needlenose) and twist. It will come right off.

The filter had a dent in the base, so I couldn't unscrew the retaining ring on the glass to remove it. That would have saved me from having to use a hammer. Once you cut the ring, it's easier to unscrew it with pliers—it's amazing how sturdy the structure is.

 

[Andreas Thaler]

Here you can see how these filters are constructed. It’s a fine example of precision engineering and is therefore worth preserving.

Screw-on filters with retaining rings: Complete cleaning

As a by-catch to lenses, screw-on filters also come into the house from time to time, which the previous owner used as an extra to protect the front lens. You quickly remove them (as long as they aren't stuck) and put them aside or even throw them in the trash. Especially when, after decades of...

www.photrio.com

 

[koraks]

The filter had a dent in the base, so I couldn't unscrew the retaining ring on the glass to remove it.

@Patrick Robert James is right, though. Once you remove the glass, the ring does generally become easier to turn. This is because the glass helps to bolster against the compressive force on the edges of the filter ring. Remove that fortification and the filter ring ends up being much, much less solid and can generally be removed. I've done it that way, too, without cutting the ring itself. Grab it with pliers and it'll basically just twist out just like it did for you. Next time when you have a really stuck filter, give it a try. The grinding can always be done at a later stage if all else fails. This also avoids accidentally breaking the glass with the grinder, which could send tiny splinters of glass flying around.

 

[Andreas Thaler]

I see, perhaps I wasn't clear enough in my description.

The process involves loosening the retaining ring with the lens spanner and then unscrewing it.

To do this, I rotate the filter and hold the ring in place against one of the grooves with a flathead screwdriver. Then the glass can be removed, and the remaining filter can be unscrewed from the lens thread using pliers.

The cut helps ensure that this twisting motion with the pliers enlarges the already weakened structure of the filter at that point and concentrates the torque on that spot. This allows the filter to come off, but it still requires some force.

Since the filter had a dent on the side in my case, I couldn’t unscrew the retaining ring and had to essentially smash the glass with an emergency hammer (like with a fire alarm) to remove it.

The cut can be placed precisely, which I didn’t quite manage to do.

Of course, the methods you described also work, as you have confirmed.

---

In my case, I’m also a big fan of the Dremel and prefer to use it and the small Dremel Stylo.

The same goes for my cordless screwdriver, which is helpful for loosening screws—for example, the glued bayonet screws on the Nikon F4 or the many screws on motor covers, etc. It takes the strain off my hand. The prerequisite is that the torque of the cordless screwdriver can be finely adjusted.

I love using tools like these. As well as a butane torch with a hot-air nozzle for desoldering electronic components. It helps you get used to working with high energy and is a challenge that provides good practice.

It’s clear to me from our discussions that not everyone sees it that way. But for me, unconventional methods and experiments are part of the process.

The advantage I have is that I work exclusively with my own cameras and equipment, not with my clients'. That gives me the freedom I need to do so.

 

[beemermark]

As a Nuclear Engineer I think you'll detect radiation in about everything