disassembling large lenses

[Vipitis]

So, as I finally try to move on with my project, repaired the shutter, gave up on getting digital/serial, resoldered by custom video cables, 3D printer died so I won't print a housing... (details here) my current roadblock is the 150mm lens being attached to the high resolution core.

I though to make this a new topic as it may attract some new readers and is easier to see for those that know what they are doing.

the core is attached to the 150mm f/1 lens on what I believe is a custom machined platform that the core screws into. From the smaller resolution core I got some idea of what the sensor side of the core will look like. Trying to find some information on the internet is really difficult as this must have been build somewhere between 2006 and 2009 and you rarely get a manual on google. I did find however a drawing here: https://www.x20.org/mwir-long-range-cooled-3-5um-micron-zoom-cameras/150mm-f1-germanium-zoom-lens-lwir-2/ which does look very similar to the lens on my desk right now. Note however that the label "release button" is just a custom cable management piece.

It is a motorized lens and I took all accessible screws off. The core does not remove and the only thing that has caused is the front group (with the motor and gearing) now sliding around in the plastic housing. This group is only stopped by the cable so it is not dropping onto the large front element. What is bad however is that the 3/8" mounting thread did come lose and now a piece of machined metal is rolling around inside the lens, likely scratching the front element. Only a few tiny screw holes allow me to look inside and I don't see any hints of how one would remove the camera.

I believe that the core module is only attached to the rear of the housing and the lens elements being in two groups. If it comes to the worst I will saw the plastic housing in half and free the lens from inside, as I think there might be hidden screws directly into the core. A long term goal of mine was to rehouse the lenses either way. But that will likely cost 2k-3k € to get done professionally and a lot of weeks to do with my friend and his new lathe.
There is a small chances it is glued but a larger chance it is just fused over the time.

I will post some pictures in a reply tomorrow.

My question is to all those out there that have the chance to get their hands on large lenses(100mm+), what were the mounting system like - are there any hidden mechanism I should look for?

[eKretz]

First thing I would do is remove the front lens element and get any loose pieces out of there immediately. That will likely be held in by a threaded ring - look for little notches that can be used to unscrew the ring. Once that ring is out you may have to contend with silicone or similar sealant around the lens element between its outside diameter and the inside diameter of the lens housing - working a thin razor blade around and down into the joint can help with that, just don't slip and scratch the lens or cut your fingers. Once that is out of the way you may find you have access to any hidden screws. It would probably be a good idea to mark the orientation of the front and rear lenses to each other if that is still possible also, as they may have been clocked to each other in the optimal position for image quality.

[Ultrapurple]

Like eKretz said.

Also, if by any chance you have access to X-Ray equipment then that's an incredibly good way of finding otherwise hidden screws. (I know this from first-hand experience, after waking up from a general anaesthetic and discovering that one arm was suspiciously heavier than the other - and now sets off metal detectors...)

[Fraser]

When approaching a challenge such as this, I always consider the needs of the manufacturer. If something is very hard to assemble, it is inefficient in terms of production time. A manufacturer will normally assemble a system in a logical and linear way that is most efficient in terms of time and energy. If something is very difficult to assemble, the person doing the task may make mistakes or find the task too challenging altogether.

In the case of your lens........

There are a few mounting methods to be considered.....

1. Screw thread mount. These can be screwed on and then locked in place using a thread lock varnish, locking screw (sometimes a tiny grub screw) or just a friction plate.

2. Bayonet mount. The Bayonet mount is used on some professional thermal cameras and is a well proven design. The lens is locked onto the camera either by a retractable locking pin or just an indent in the bayonet contact surfaces. Friction bayonet mounts using spring steel ripple washers also exist. Sometimes a bayonet may have locking varnish added to prevent movement due to vibration.

3. Sliding mount with locking band or screw. These are quite crude, but effective. The lens is an interference/sliding fit into the lens mount tube. The lens is adjusted for back focus and locked into place using one or more grub screws through the mount tube wall or a locking band that tightens down on a slotted section of the mount and so compresses it against the lens tube.

4. Bulkhead mount. This uses a flange on the lens that is attached to the camera using screws. This is a very rugged and stable mounting method, commonly found where high levels of vibration may be experienced by the camera system. The screws that secure the lens flange to the camera may be orientated outside-inwards or inside-outwards. That is to say, they either screw into the cameras chassis from outside the camera or they screw into the lens flange from inside the camera.

You need to consider what mounting technique makes sense in your particular case. A mounting flange type system can be all but invisible if the screws are of the inside-outwards type as the screw heads are hidden inside the camera casing. Then you consider how the camera and lens are assembled at the factory. The manufacturer is unlikely to completely strip a lens or build it in-situ just to mount it on a camera. That makes no sense and is risky to the lens. I doubt you would find a lens that has its barrel mounted and is then populated with the fragile lens elements. More likely the lens is a complete module and is attached in its entirety to the camera without any disassembly or assembly required to the lens. This would suggest the front plate of the camera uses one of the methods detailed above. If it is a flange mount, the screws will be found around the Microbolometer aperture and are likely accessed by removing the camera casing and either using a long screwdriver or some PCB’s are moved to provide access.

Fraser

[Fraser]

I just took a look at a picture you posted previously of the large lens. More pictures of it woukd assist in making a decent assessment of the lenses construction but I believe I know enough to help were move the front lens element if required.

OK from what you have said, removing some screws released a mounting plate inside the lens barrel. Can you rotate the lens and tilt it to manoeuvre the part into view through the barrel drilling’s ? If so, use a paper lip or similar wire to manipulate the plate into position for refitting they screws. This is a challenge that I have Previously undertaken and have never failed if patient.

If all efforts fail, you will be able to remove the front lens element, but it will be a challenge and risky fir the lens element. This looks to be a fully sealed lens Front and does not use the usual under all locking ring. I believe it will use a complete lens barrel front section that contains the lens and screws onto the rest of the barrel with an internal thread. A bit like a threaded rear lens cap. If it is not that exact design, it may be a complex cross section Internally threaded ‘U’ profile cross section locking ring that clamps the lens element in position.

Both designs will be sealed with an appropriate weather sealant and will be challenging to unscrew. I use special rubber straps that go around the lens parts and grip it tightly without damage. Handles on the straps apply the turning force to overcome the sealants grip. It is not always easy and it carries risk that is best avoided if possible. Hence try to fish that loose mount part back into position. In the long run, it may take time but it is the better solution.

Fraser

[Fraser]

The rubber ‘wrenches’ that I use look very similar to these from Duratool. Not expensive but great for disassembling threaded pipe sections and lens barrels. I bought two sets so I have two of each size fir tasks.

https://cpc.farnell.com/duratool/d00070/strap-wrench-set-2pc/dp/TL10279?mckv=sCZwpuUiZ_dt%7Cpcrid%7C224686838591%7Ckword%7C%7Cmatch%7C%7Cplid%7C%7Cslid%7C%7Cproduct%7CTL10279%7Cpgrid%7C45804914126%7Cptaid%7Cpla-893434214619%7C&CMP=KNC-GUK-CPC-SHOPPING&gclid=CjwKCAjwj975BRBUEiwA4whRBzVzsGikPYMX4dvLIWXxSFpO2afIQU_8qhCQd2A96p0vZ1KeH0VfGxoCDQ8QAvD_BwE

On eBay just look for “strap wrench” and you will find many offerings

Cheap as chips 

Fraser

[Fraser]

The strap wrench in use...

https://youtu.be/wfKHz1yf1uI

Really useful and they come in different sizes to suit a range of tasks.

Fraser

[Fraser]

My set looks like these but I bought mine from Aldi. Not a bad price and they can even grip a camera casing whilst using another to apply torque to the lens barrel to undo it. Great bits of simple, inexpensive kit 

https://www.ebay.co.uk/itm/Stag-Tools-Two-Piece-Adjustable-Strap-Wrench-Set-150mm-100mm/274401988326?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D225075%26meid%3D45c08a6c2bb740ff87b6f72f8bcf4207%26pid%3D100675%26rk%3D1%26rkt%3D15%26mehot%3Dnone%26sd%3D274401988326%26itm%3D274401988326%26pmt%3D1%26noa%3D1%26pg%3D2380057&_trksid=p2380057.c100675.m4236&_trkparms=pageci%3Ad5beed30-df18-11ea-9f95-74dbd180c680%7Cparentrq%3Af310d97a1730aca47754723effffe658%7Ciid%3A1

Fraser

[Vipitis]

thanks for the tips. I am sorry that I haven't been able to post the images I promised. Just had something else comeup over the days. I did find some hints of the for hidden screws in the machined metal block or "flange". I can't really see inside or even get a photo of inside. but I see the uncoated rear side of the huge Ge element and some dust on it.

It's actually not plastic but powder coated aluminium. I really hope there is a solution to not destroy the housing, but just need the tools and strengths. I would rather destroy the housing than the front element.

In included some images, aggressively cropped to post them. But I might be able to get some more detailed shots with a different lens, as I got a new camera recently it is always a challenge. Don't have access to any x-ray equipment so we will only find out about the insides when it's opened up.


will look for some pictures of the smaller core when I took the lens off to highlight how that is attached to the core for a reference.

[Vipitis]

more photos here: showing the smaller core and how the lens is mounted there, as well as a drawing of a CAD model I have found a while ago.

I am expecting to find something rather similar on the bracket of the 150mm lens

[Fraser]

On the large lens you have removed some screws at its rear. These appear to hold the rear section of the lens to the main barrel. I would expect that rear flange of the large lens to dismount and provide access to the hidden screws that hold it to the cameras lens mounting flange. The rear flange on the lens may be an axial sliding surface or butt facing type mount that is well sealed to prevent moisture ingress. Some force may be required to break the seal. With the Screws positioned as they are, I would not expect the rear flange of the lens to use a threaded mounting between it and the lens main barrel.

Fraser

[Bill W]

Two observations - just in case you had missed them.

The cable entry includes an equivalent of the 'release button' on the drawing.

The drawing is a bayonet mount, so the machined block should rotate away from the larger lens part, but may well have set / seized over time as there's almost certainly a seal in there.

Any luck digging out that filled screw head in the machined part adjacent to the 'Miricle' on the core- maybe that locks the rotation of the core mount block ?

Also a chance that the front lens comes away as a whole cell somehow, leaving the (?) plastic cone behind.

Bill

[eKretz]

After the new photos, I think Fraser is probably right. Those removed screws are likely what held the back of the lens housing together. If it's not slipping apart, it is likely only held by sealant. Try giving it a twist. It may be held pretty tightly though.

[Fraser]

Good spot Bill. I had thought those marks on the lens mount were hollow tip grub screw impressions from a bracket that held the camera assembly in its original housing. Maybe not. Vipitis ... are these witness marks from hollow tip screws or something else ?

I believe the ‘pin release’ mechanism is not fitted on this particular lens configuration. The lens can be provided with custom rear mounting designs that are mounted to the lens body using the four recessed screws that I mentioned earlier. That is why I believe that whole aluminium rear ‘flange’ mount decouples from the rest of the lens assembly. It is a smart design by the lens manufacturer as it makes the lens effectively a ‘universal’ mount design with easy adaption to meet the customers needs 

Fraser

[eKretz]

I noted those marks as well. They definitely look like impressions from the end of screws that bit in at first glance. Perhaps could be a pinned fit too... Any chance of some closer-up shots of those areas? How many are there?

[Lord of nothing]

I know this from first-hand experience, after waking up from a general anaesthetic

pls be carefull next time you might wake up without a Kidney!

[Vipitis]

yes, there are two marks. Opposite of one another directly below the MIRICLE logo. The one pictured first is definitely the tip of a screw. Not sure what it's purpose it, but I think I doubt it's meant to be accessed from outside. Drilling that open could be an attack vector but I am worried about more metal pieces falling inside the lens cavity.

The mark on the opposite is just a dent from maybe some tool. Or it's a surface the mounting block was pressed against. Not a screw there.

I have tried to twist, push and pull the mounting block against the main cone. But nothing. Maybe it's glued/sealed so I will give it a try with some heat and hope for the best.

While I won't be arround for the next few days I want to thank all of your for the guidance. It's not progress but it's also not doing nothing and if there doesn't seem to be a solution. I will saw it in half and access the insides.

[Fraser]

Hmmmm, tip of a screw or locking pin ? The edge of the hole is chamfered which is normally done on the side a pin is inserted and not the exit point. The insert is flush with the aluminium in which it is inserted. Not common for a screw at its exit point. This has the appearance of a solid pin that has been press fitted into the aluminium flange using a pin press and the witness mark on the opposite side may be from the pin press fixed die.

This could suggest a very unpleasant pin locking technique for the lens or it could suggest a course spiral or some form of bayonet mount. I would be surprised if the pin is a locking pin as that is really service unfriendly and hard to remove.

Fraser

[Fraser]

Just thinking about this a bit more. That looks like a classic alignment pin deployment that is used to guide the rotational alignment of two tubular components with respect to each other. One part contains the pin and the other part contains an alignment slot. If this is true, I believe the lens mounting is axial in nature and separation would be via tension applied by a puller tool and not by rotational torque.

It would be worth removing the electronics package and Microbolometer from the cameras chassis and pushing the FFC flag out of the way so that you can see the inside of the lens mounting arrangement. It might provide some clues and save your lens barrel from damage. This is where an inspection borescope comes in hangs but you may be able to peer through the Microbolometer aperture With a torch to see enough detail of the mounting design.

Fraser

[Fraser]

If you remove the sensitive electronics from the camera, you can gently tap the area of the lens mount with a padded tack hammer to see if a gap opens up to reveal the separation point in the design. Do not be too enthusiastic with the hammer but sharp shocks can sometimes release lacquered or age dried seal joints.

Fraser

[Vipitis]

If it is a locking pin, it shouldn't be easily removeable from the outside. But I would have to look at a view examples to understand the geometry and the mechanism.

There is one difference between the 110k and the 307k core. And on the image I send form the 110k core you can see below the shutter flag and onto a bit of tape that is essentially a hole to the outside of the core. Such a hole is not present on the bigger 307K core. It has a protective cover fitted below the lowest pcb. The whole point of this operation is to get the camera core off the lens to use it with the other lens instead. And I can't take off the bottom pcb of the stack without accessing the sensor side of it.

[Vipitis]

Update Report: First success with combined forced my brother and I have been able to take the camera and it's mounting flange off off the rest of the lens. It turned out to be glued on, no screw thread. The core is functioning and shutter works. We are currently fighting with one screw to put the 32mm from the other core on for some comparison shots. Coming later^^

The lens however has a small rim and within destructing that I won't be able to take the the optical block and zoom motor out. It is likely filled from the front with the front element and it's mounting ring put on last. How that will be disassembled is another quest but I got some ideas. I am looking for professional rehousing anyway, if I find a partner for it.

Photos from the lens, flange and core will come soon. how soon I will be able to do side to side comparison shots is still up I the air right now. As my capturing solution already messes this up a lot.

[Vipitis]

as promised: the pictures.

the rear of the lens with the camera and core remove. the rear optical block is now moving freely in there.
the flange still attached to the camera core, revealing the "hidden" screws that.

example videos with the 307K core are in the works, will likely post one or two example pictures to the gallery thread.

[Vipitis]

Further update:

I haven't managed to take the front element off, so I ended up sawing the rear off. After a while I manage to just use the jaws from some pliers and tear off the little lip. I was able to take out the rear group and get the motor off.
 It's a smaller element than I thought. I am not not sure yet if it's just 1 or actually 2 elements the in the rear group. The rear is concave and the front of it convex. The little focussing mechanism it is in allows for 180° twist and about 10mm of travel. I decided it keep the assembly for now.

I removed the debris from the remaining lens housing. But don't see a way to undo the front element. Perhaps it is glued after all.

At this point I plan either heavily modified the housing (for manual focus operation and a lens mount). Or do rehouse it completely.

I want to give it a few test, but it's a setup of holding 3 things in your hand more or less. So maybe that will be uneventful.

See some photos I took from the disassembly below.