chipped lense I think....

[peytr]

I got a not too rough example of the Baker Patholette last weekend. All works well, needs a clean and the usual TLC but I couldn't get anything of a picture with the 40x objecive. Just inspected it with a loupe and I think the front lens is chipped.

Please take a look and let me know what you think.

I ordered a second hand 40x objective in the mean time and hope for the best.

[75RR]

Never seen that before - looks perfectly round and perfectly centred.
What does the image look like through that objective?

[wporter]

It looks like something is on the surface of the lens, making it wavy. Could it be a dried contaminant? Maybe someone tried to use it with immersion oil? Try cleaning it with a Q-tip with some acetone on it.

[zzffnn]

Usually a minor chip, delamination or dried oil won't render an objective not capable of producing image.

More photos of the top lens and back focal plane image (shot through phase telescope with dime light) will help diagnosis.

Won't hurt to gently clean it.

apochronaut may be able to tell you more.

[peytr]

Yes it looks perfectly round and a bit wavy. I read (before buying) these Patholettes do have a problem. The table is resting on a lever which regulates the height of it. Works like a dream because there's no spring, only gravity. The disadvantage of that is that you can move the table up and against the lens by adversely lifting the scope by grabbing it under the table. This will happen with force because it is not a light weight scope. It is a problem because it hardly has features to hold on to so will happen sooner or later.

To answer your questions: I'll try cleaning but such a front lens should not have a concave spot, should it?

I can hardly get any image from this objective now. The other objectives (3x, 5x and 10x) all work well and only need cleaning. I tried the objective in different positions and with different scopes before taking a closer look.

Ah, good idea.. I have a phase telescope somewhere and I van take a closer look with that as well!

[peytr]

Just got the objective I bought as a replacement in the mail. This one is OK and didn't cost me an arm and a leg.

Looking at that objective I can see that there is another element with the flat side out, probably kitted to the surface we're looking at on my defective one. I can clearly see the same shape when I hold it but I think I cannot take a picture of that.

The waviness in the concave bit must be old kit, I guess.

Problem solved. Unfortunately no cure for the damaged one, I'm affraid.

[apochronaut]

Is your replacement a Cooke-Baker or Vickers cover slip corrected microplan? The one you picture is a microplan and that objective has a concave facing surface. The front element looks similar to a classic volcano shape, with a conical glass element , topped by a concave first surface. Looks like your fouled objective just needs a good cleaning, as earlier suggested. Probably got dipped into immersion oil that subsequently hardened, the most common failure of high-dry objectives. If you did not receive a 40x .70 microplan as a replacement, I would be cleaning the microplan. Those are very superior objectives, for any D.I.N. 160mm system.

[peytr]

Thank you Apochronaut, that's very interesting.

The replacement is a Vickers, doesn't have the Microplan designation but looks exactly the same as the Cooke Baker Microplan, which I photographed. The Vickers (replacement) shows the same 'crater' or concave section, albeit behind a flat glass surface. I doubt if I can get a good picture of this but will try.

As said I'll try cleaning but want be do this with caution. It is such a beautiful thing that I would never forgive myself for damaging it while trying to save it

Regards,

Peter

[Rodney]

Another very good option is to place the objective in a rubber clamp lab stand and place it under a stereo microscope if you have one or know someone who has.
Send a light up from the other end of the objective in question and focus the stereo microscope in the area of question.
Take a close look at 10x or a little higher magnification at any problem you possibly could have. More than likely you will eventually be able to tell if the objective glass has been damaged or just needs cleaning.
Rodney

[apochronaut]

Thank you Apochronaut, that's very interesting.

The replacement is a Vickers, doesn't have the Microplan designation but looks exactly the same as the Cooke Baker Microplan, which I photographed. The Vickers (replacement) shows the same 'crater' or concave section, albeit behind a flat glass surface. I doubt if I can get a good picture of this but will try.

As said I'll try cleaning but want be do this with caution. It is such a beautiful thing that I would never forgive myself for damaging it while trying to save it

Regards,

Peter

The Cooke-Baker/Vickers standard achromat, came in a 40x .65 version mostly but I have seen a 40x .70 phase version. Both of those had a conventional plane surface on the front lens. This type of conventional forward lens surface is typical for a non-plan objective. Designs for better plan performance often demand that the front element have a concave surface, which is the design Cooke-Baker and successor Vickers used for the 40x .70 microplan objective.

Rodney's system works well but if you do not have access to a stereo mic. an alternative is ; using a reversed eyepiece as a magnifier, a common household solvent, such as isopropyl alcohol and good quality cotton swabs, you can get an idea, how persistent the residue is and most likely be able to clean it with those tools. Usually isopropyl will dissolve old hardened oil, with a bit of a wetting period. Isopropyl, will not harm the coating. If light rubbing with the soaked q-tip doesn't remove anything, when viewed with the reversed eyepiece, then set up the objective on it's threaded end and find another object about the same height and place near to it. A wine cork will do. Soak the swab in the isopropyl and lay the wet end on the objective end, resting the other end on the cork. You can cover the end with a little sheet of plastic to slow evaporation. After about 5 min., try gently wiping off residue again with the swab. If anything at all looks like it is being removed, keep at it. If not, up the solvent strength to ethyl alcohol. Vodka will do. That lens is perfectly safe to be cleaned with ethyl alcohol. The optical collecting surface on that objective is quite small, so the best method of cleaning is to place the swab on it's end and rotate it back and forth between your thumb and finger(s).

[peytr]

Long time since I started this thread. I finally cleaned the outside of the lense and I do get an image, but still not very clear. When I look into the objective with a loop there is all kinds of debris in there (perhaps fungal growth, I'm not sure). It became clear that this objective has seen quite a lot of abuse. I don't exactly know about the former lives of this microscope but I do know I bought it from a farmer in a rural area.

Anyhow; I'd still like to try and rescue the objective and tried to understand how to take it apart but I cannot figure it out.
I can screw off the bottom ring, which exposes a brass thread but nothing else seems to happen.

I can take out the screw in the top of the objective and then I can turn the main barrel but I cannot understand what this screw is for and how to proceed (and what the turning of the main barrel is for).

Can someone point me in the right direction for taking this objective apart?

Best regards,

Peter

[Chas]

The nose is spring loaded ....does the nose (i.e. green ring and forward of it) move in and out... or is it seized?

[peytr]

No, it moves freely. The lock screw or the front ring on or off doesn't make a difference.

Microplan objective.png (112.86 KiB) Viewed 2168 times

[Chas]

You need to unscrew the black disc
Before you attempt this it might be a good idea to put a drop of cigarette lighter fluid at the edge of the disk and leave it for ten minutes to work its way down between the threading.

(Lighter fluid is distilled [Swan even claims to be 'double distilled'] so shouldnt contain oily stuff that could find its way onto your glass) . but if you only have WD40 ..apply it with a matchstick.

I dont know if you have a lens spanner, but they are very helpful:

Lens spanner.jpg (27.26 KiB) Viewed 2146 times

Once you have taken out the little screw and removed the black disc, by screwing it out with something like the lens spanner, a large spring will appear and below that there is a brass barrel that has the all the optics inside it ... gently push on the nose of the objective and everything should come backwards out of the threaded end.

One word of caution dont try to clean the back of the rear element of the lens until you have blown the grit off it, think rust, dust, sand. ( a squeezey lens blower isnt bad but there maybe better things).

If one objective has grime on its back surface then the others might have too ..so the lens spanner might get more than one use

(Take some pics with your phone as you are taking things apart, just a good idea to save anxiety, later ). But you shouldnt need them for this job / objective. (famous last words).

[apochronaut]

There is a good chance there are thin shims between certain lens cells, especially between the front lens and # 2 and between #2 and #3. These are individually adjusted for each objective at the time of assembly in order to optimize spherical aberration, so those shims need to be kept in the proper order and number upon reassembly.
There may also be scribe marks down the sides of the cells, which are made after the lens cells and shims are manually aligned rotationally in order to obtain optimized centering. Not all objectives have these but if yours does, it is a good idea to register the location of the scribe against a fixed benchmark on the outside of the objective and when reassembling, line everything back up as closely as possible to it's original location.

[peytr]

Thank you Chas and Apochronaut,

I do have a lens spanner but I need to find it. It's missing in combat, one might say. OK, I wondered because the black ring doesn't have two holes, only the one with the screw. I'll give the lighter fluid a try because I tried to move the upper disk before and it wouldn't move.

I'll give it a gentle try with the info you supplied and see what happens.

Will let you know how things develop.

[Chas]

Peytr, I now realise that there is more than one design of the construction of the objective barrels:
I have a Baker labelled objective that has the concave front lens and this has two round holes on the back disc (for the lens spanner).
A Vickers labelled objective with no holes on the back disc... these look as if they might split along the chrome barrel, a couple of mm below the knurling.
A Cooke labelled 40x that I cannot see how it comes apart
So apologies for thinking it was simple.

[apochronaut]

I believe there were two versions of the 40X Microplan. A .65 version and a .70 version. Is that the difference in the assembly design?

[Chas]

I believe there were two versions of the 40X Microplan. A .65 version and a .70 version. Is that the difference in the assembly design?

I dont know, I only have one (Baker) 40 0.70 Microplan (with two round pin spanner 'holes' )

I wonder if the back plates without the extra pin spanner holes are a Vicker's thing; why drill 3 holes when you can get away with one, for general lenses. Only need a special tool to spin the disc into place, once.

peytr's lens is presumably Vickers as it is labelled Cooke-Baker(?)

On the subject of special tools I came a cross a DIY/hack video where someone made a pin spanner by putting the rear end of drill bit(s) into the pin hole(s) and then squeezing in some warm polycaprolactone modelling-granules. A 2.6mm drill bit seems a tight fit into the single hole, so I guess that a 2.5mm might do. Having said that it looks as if the caps had some additional black paint put on the after they were put into place as there some faint traces of it on the internal threading .. and even using a pin spanner on a double holed cap it needed the threads cleaning before the cap would screw out ( I used a glass fibre bristle pen). I didnt put any PTFE grease on the thread first, but it would have been a good idea.

UPDATE: I have just tried a 2.5mm drill bit 'set' in some of these granules on a single hole Vickers and it worked ! The stuff didnt grip the drill bit at all, but applying pressure on the drill bit's sharp end by pressing against the edge of a table, to hold it in the disc's hole, whilst turning the blob of of plastic, was enough. I had fed the thread with lighter fluid during the day.

I think it is worth seeing despite its ugliness;

The attachment Polymorph and drill bit.jpg is no longer available

It moulded itself both into the central hole and around the outside of the ojectives thread:

Polymorph drill bit spanner.jpg (21.2 KiB) Viewed 1830 times

The material is sold as 'Polymorph' in the UK