Question Regarding Darkfield Condensers

[apochronaut]

Odd question but if you had the capacity to examine or the experience of examining Spencer catalogues in some detail, let alone the experience of using Spencer equipment you would realize that you would look long and hard to find that interchange. It would be nice wouldn't it be? Just pop out the BF condenser and pop in the DF condenser. No, the DF condenser lives in it's own mount and fits into the dovetail vacated by the BF condenser. Yes, the DF condenser has a machined dovetail on the bottom, which isn't expressly designed to work in the 1.30 achromat housing but it actually does quite accidentally. That's just another way of helping to solve John's dilemma by providing a non stat. solution. He seems to otherwise not have the parts to make it work or for some reason does not want to adjust his DF condenser out .
You know it isn't just that I have used a Spencer # 5. As I said , I have used one in all possibilities and for many years and currently own more than one , so I know the system quite well. I just reconditioned a # 3 for sale and it is a smaller #5. Functions similarly
. Maybe you should buy it? Using it might give you a grounding and you could be able to confirm which way is up on a dovetail.
Solutions for this type of problem are usually quite straightforward and based on precise mechanical relationships. DIY solutions involving tube and tape and hot glue etc. are of value where mismatched or otherwise diverse components are being assembled. There is no such situation here. You just follow the dots. Simple mechanics.

[J_WISC]

John has low confidence and fears breaking something ever since he broke detent on the antique Spencer Buffalo.

Also, I briefly panicked when a spring jumped out when I took something apart.

The DF lens integrated into the dovetail, with the centering screws below the dovetail, is very intimidating. So I was hoping for an easier fix.

But now that I have photos of the interior, I might have the courage to do the right thing and extract the DF from the dovetail so I can easily swap BF and DF condenser lenses as needed.

There is hope for me. Thank you everyone for your help.

(But still thinking about an extension tube for other reasons. )

[Chas]

Just pop out the BF condenser and pop in the DF condenser. No

It would be nice wouldn't it be?

......Tooo nice, the manufactures might say. (and if you really want the freedom to use a standardised condenser you are going to have to purchase a special mount ).

Of course they each maintained other dimensional differences that would keep you on the straight and narrow

Maybe you should buy it?

At the moment I would love to have any microscope with a fine-focus control for the condenser


J_WISC .. Even though I was aware that the fine focus spring in a Bausch and Lomb was under tension, the unexpected speed and ferocity with which it sucked its holding pin down into the frame, shocked me*.
Have you managed to turn the threads of the DF condenser head? MichealG once recommended 'PlusGas formula A' liquid for freeing up threads and it is good.
(my Leitz DF sat unused for 18 months until I bodged it into another centering mount ...)

* reminded me of this Bobbit worm clip:
( https://www.bbc.co.uk/programmes/p05mg8j9 )

[apochronaut]

John has low confidence and fears breaking something ever since he broke detent on the antique Spencer Buffalo.

Also, I briefly panicked when a spring jumped out when I took something apart.

The DF lens integrated into the dovetail, with the centering screws below the dovetail, is very intimidating. So I was hoping for an easier fix.

It is quite a simple system. There almost no spring pressure once the thumbscrews are backed off to where the ends clear the dovetail or rounded chamfer on the condenser housing bottom. They cannot fall out and the kind of omega shaped leaf spring just stays put when the condenser body is removed out the bottom. Once the DF condenser body is out, you don't really need the DF condenser centering mechanism any more, if you are going to be placing the DF condenser into the BF condenser well for use.
There is about a 1" hole in the top of the centering plate once the DF condenser is removed, so the spring could fall out if the part was moved around or handled. I would just plug the hole with something or put a piece of tape over it and put the part in a small box, clearly identified.

[apochronaut]

Just a little extra Spencer # 5 context from a couple of old threads. There were two Spencer # 5s, each one being the flagship research microscope of it's day. The older one quickly slipped into obsolescence after W.W. I to be replaced by the Spencer # 7 for about 10 years until 1932 when the # 7 was by then past it's prime and the new # 5 arrived with it's revolutionary low fine focus.

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viewtopic.php?f=24&t=1042

[J_WISC]

Slight tangent, since the fine adjustment for the condenser entered the discussion.

Can someone please briefly describe proper use of the fine adjustment for the condenser on a Spencer Research Microscope? It's possible I don't know what I actually have or something is missing.

Here's an image from a 1946 Spencer catalogue (note the "fine adjustment" knob):

1946.jpg (53.82 KiB) Viewed 13291 times

This is close to what I have (mirror removed):

condenser_holder.jpg (57.18 KiB) Viewed 13291 times

Here is the condenser holder removed from the microscope:

removed.jpg (86.94 KiB) Viewed 13291 times

I originally thought the sliding dovetail was SEVERELY gummed up. But after loosening the grease, I found it moves only a few millimeters up or down relative to the primary rack. There are hard stops blocking further motion, and they're impossible to reach without further disassembly. Furthermore, being very naive, I assumed there was a gear in there. There isn't. I finally found the courage to remove the (reverse-threaded) knob and the black bracket. The knob just threads through the bracket and serves as a set pin to stop the sliding dovetail, which you have to move directly by hand.

set_screw.jpg (60.38 KiB) Viewed 13291 times

So ... I MUST be missing something, mentally or physically. Because it is difficult to see the value of moving the ultimate condenser holder a few millimeters up or down relative to the rack. Wouldn't a person just adjust the stop for the rack? OR ... once close to the bottom of a slide, did the user gently push the holder up a bit more and lock it with the set screw? Or is there a part missing?

I might have just answered my question while typing this out. Gently push upward to just below slide and lock in place ... right?

THANKS!

(By the way, screws holding condenser dovetail ring were damaged and so firmly stuck, I had to temporarily replace them with new set screws. I apologize for the poor aesthetics. Proper screws cost more to ship than cost of screws. Also, beware! There are tiny springs holding tiny pins in there!)

[apochronaut]

Your post confirms a couple of suspicions that I had. The first is that the condenser stop is set high , which conversely will stop the condenser yoke at a lower position.
In order to bring the DF condenser ( when still assembled in it's own mount) to proper oil contact with a slide on the floating slide carrier, because it is a bit shorter than the BF condenser, it needs the maximum height settings. The stop needs to be adjusted to it's minimum, which leaves the locknut and adjustable screw at the same level. Right now, your screw is sbout 6 or 7 threads above the locknut.
The screw has a slot on top for turning in and out and the locknut is unfortunately round with a split slot on either side ofvthe screw.. There are special wrenches with which to free up the locknut but once loosened they aren't really needed, nor if already not very tight . The tip of a small screwdriver or nailfile or other small device can be put into one of the slots sideways to retighten it or often just the fingers will do it . To loosen it initially if stubborn without the proper split screwdriver or tiny pin wrench , use a small set of pliers or hemostats with a couple of pieces of protective electrical tape on the jaws, or most often a small screwdriver turning out the stop screw will bring the nut with it . It can then be adjusted level with the top of the screw and tightened down. This will get you 3 or 4 mm maybe more.
A bigger problrm is the fine focus, which I suspect is stuck at a low point. I have not disassrmbled one but based on the design of some of Spencer's other older fine focus mechanisms, it is likely a worm and nut design which cantilevers a moving apex up and down as the screw is turned with the knurled knob. Possibly the nut has dropped off the shaft or has been lost somehow. I can check on that for you but for sure, based on your photos, the yoke sits low on the dovetail, so getting that working will gain you another 5mm or maybe more.
I don't know what stage you have. There were I think 7 possibilities and the fancier ones have what they called a floating slide carrier, which elevates the slide sbove the stage surface a little. With this type of stage, the condenser top lens needs to rise above the stage surface a few mm more than normal, so the maximum height is needed.

I think I may have an orphan condenser yoke here from another model. If it is the same as that on the # 5, I can send it to you. The spring loaded fingers on the dovetail yoke is a feature you should have.

[J_WISC]

A bigger problem is the fine focus, which I suspect is stuck at a low point. I have not disassembled one but based on the design of some of Spencer's other older fine focus mechanisms, it is likely a worm and nut design which cantilevers a moving apex up and down as the screw is turned with the knurled knob.

Good evening. Setting aside the DF matter for a bit, I tried dissecting the condenser fine focus. And here's what I found. It is a very interesting mechanism.

Interior when knob is turned in as far as possible:

high-interior.JPG (164.14 KiB) Viewed 13183 times

Interior when knob is turn out about 6 mm:

low-interior.JPG (164.96 KiB) Viewed 13183 times

The fine focus is highest when the knob is in as far as possible, and drops about 2 mm when turned out.

high-exterior.jpg (182.5 KiB) Viewed 13183 times

low-exterior.jpg (206.56 KiB) Viewed 13183 times

Is this likely the normal operating range? I don't see an easy means of further dissection and I'm thinking "sort of" working is probably better than not working at all.

THANKS!

[MichaelG.]

An interesting little mechanism … thanks for sharing the photos

MichaelG.

[apochronaut]

The range of movement needn't be very much since it is a fine focus. The bigger problem is the travel stop or travel limiter that is visible at the top of the two last pictures. As already mentioned there are 7 threads visible above the locknut. That needs to be lowered to the level of the locknut or removed altogether. The condenser yoke height is being limited by the length of that stop.