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PostPosted: Wed Apr 18, 2018 9:17 pm 
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This is a good thread Hobbyst46, I have a seriously degraded mirror in one of my external OLY lamps that will need a fix one day, I saved this out for reference.


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PostPosted: Wed Apr 18, 2018 9:36 pm 
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MicroBob wrote:
Cutting wood with an abrasive wheel generates lots of smoke - I would prefer the tape.
You can glue a strip of wood on the tape as a guide.

Sorry for being vague. What I actually thought was to put some protective tape on the coating, clamp the mirror between two thin plywood (or aluminum) pieces, mark the required size and cut through with a fine-tooth hacksaw, and finish with a fine file. A guide like you suggest is another option, if I use the Dremel tool.
Quote:
Have you tried whether you really need a first surface mirror?
No, I just trust that a first-surface mirror will be better, but how can it be checked without the mirror in hand?

@Apochronaut: Yes, a large mechanical shear is an excellent idea, with protection of the mirror as you suggest. It will be easier to get and faster than a mill, indeed. My hand shear has always deformed the tin. But the bottom line, is indeed to know first what thickness is the mirror.

Thank you both for the support!

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PostPosted: Wed Apr 18, 2018 9:38 pm 
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I'll have to try the stainless.

Another option is first surface mirrors with a glass substrate from Edmund. Tend to be pricey, but you won't need their most precise (very flat) grades. I've found cutting with an ordinary glass cutter works, but damages the coating adjacent to the cut. However, since only the central (ellipse) is needed -- doesn't usually interfere. Frankly, you could probably nibble away at the edges with end cutters and get something usable to fit.


Last edited by PeteM on Wed Apr 18, 2018 9:42 pm, edited 1 time in total.

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PostPosted: Wed Apr 18, 2018 9:39 pm 
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coominya wrote:
This is a good thread Hobbyst46, I have a seriously degraded mirror in one of my external OLY lamps that will need a fix one day, I saved this out for reference.
You are most welcome, I hope that it will prove useful, I will report on the results. The mirror is being shipped from China, via a real cargo ship I believe, since delivery time is 30-40 days...

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PostPosted: Wed Apr 18, 2018 9:59 pm 
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PeteM wrote:
I'll have to try the stainless.

Another option is first surface mirrors with a glass substrate from Edmund. Tend to be pricey, but you won't need their most precise (very flat) grades. I've found cutting with an ordinary glass cutter works, but damages the coating adjacent to the cut. However, since only the central (ellipse) is needed -- doesn't usually interfere. Frankly, you could probably nibble away at the edges with end cutters and get something usable to fit.
Thanks, PeteM. I checked with Edmund Optics. They have a 35x35x3mm mirror (the simplest reflecting type, aluminum) in stock. No need to cut it, since it is shorter by only about 5 mm (I believe) from the present mirror so it might be adequate. USA price is $23 (perhaps plus H&S cost?), but I have to call their international dept and probably ask for a quote etc. Maybe Amazon sells them.

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Last edited by Hobbyst46 on Wed Apr 18, 2018 10:10 pm, edited 1 time in total.

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PostPosted: Wed Apr 18, 2018 10:07 pm 
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coominya wrote:
This is a good thread Hobbyst46, I have a seriously degraded mirror in one of my external OLY lamps that will need a fix one day, I saved this out for reference.
Incidentally, how does one save a post ? there are great posts here that I would save!

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PostPosted: Thu Apr 19, 2018 12:31 am 
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A few years ago I bought a fairly large front surface mirror on Ebay for about $20, if memory serves. Using a hardware store glass cutter I cut a new 45 degree mirror for the internal illuminator in one of my A/O 4 Series stands. The reflecting surface on the old mirror was in bad shape. The first attempt at mirror cutting wasn't successful, but the second one was. The new mirror stock is about twice as thick as the original mirror, but I haven't noticed any problems with illumination.

There are a whole bunch of front surface mirrors up on Ebay right now. They're called laser bounce mirrors for laser light show displays. Hardly optically flat, but a small piece is giving good service in my most used scope.

There might be some sellers outside the U.S., too.

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A/O 10 Series Microstar
A/O 4 Series Microstar
A/O 4 Series Phasestar
A/O 4 Series Apostar
A/O Cycloptic Stereo
Several old monocular scopes in more or less decrepit but usable condition


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PostPosted: Thu Apr 19, 2018 6:03 am 
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Hobbyst46 wrote:
Incidentally, how does one save a post ? there are great posts here that I would save!


I run the latest firefox with the "Save page WE" add-on. I just click the button and it makes a copy of the whole page with all posts.


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PostPosted: Thu Apr 19, 2018 10:52 am 
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Hobbyst46 wrote:
No, I just trust that a first-surface mirror will be better, but how can it be checked without the mirror in hand?


A first surface mirror generally is better for this application but the question is, whether it was really part of the original concept of your specific instrument.
Zeiss was very willing to make small changes to their instruments so I would check this first. The GFL was a development of Zeiss-Winkel in Göttingen, not from Carl Zeiss in Oberkochen. This alone led to several changes over the years.

I would install the old mirror as good as possible and do the test i suggested on Wed Apr 18, 2018 3:44 pm. It should be easy to see which type fits right. A piece of aluminium foil on glass could even be used as a dummy first surface mirror.
Perhaps you can see it even without the mirror by looking at the mirror box from the side and comparing the placement of field iris, frosted lens and 45° plane by eye. The error introduced by using the wrong typ of mirrir would be quite big.

Shearing sheet metal: Difficult to predict whether your mirror will be warped or not. There is stainless spring steel and types that bend easily but still offer resistance to beeing cut.

Sawing: Good method, but you would have to use wood or aluminium of a couple of mm below and on top, otherwise the saw teeth will dig in and the border will be uneven and jagged.


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PostPosted: Thu Apr 19, 2018 11:05 am 
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Yes. I hadn't considered that they might make a dental mirror out of spring steel.


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PostPosted: Thu Apr 19, 2018 1:35 pm 
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This stainless spring steel actually cuts quite well as long as it is not too thick and it is less prone to warping.
It is used in half hard condition so the springs still can be cut and bent.
Since it is not that expensive it would be a very nice material for a dental mirror.


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PostPosted: Thu Apr 19, 2018 9:34 pm 
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MicroBob wrote:
I would install the old mirror as good as possible and do the test i suggested on Wed Apr 18, 2018 3:44 pm. It should be easy to see which type fits right. A piece of aluminium foil on glass could even be used as a dummy
Thanks, I found that post - it is shown as posted on 4:44 pm on my computer (summer time clock mismatch I believe). I will try to run a comparison on a spare stand + iris diaphragm and collector optics that I have.

@MicroBob:
What is "Stainless spring steel" in this connection ? all plain stainless steel sheets (thickness ~1-2mm) that I have worked on are usually somewhat springy, but can be bent and cut, especially with heavy workshop machines.

What I learned, with the help of the discussion with folks on this forum, is that indeed, also on my scope, the mirror can be fixed without glue, just pressed between the sloped side rails of the carrier and the cork strips on the back frame. The strips cannot isolate the mirror from heat flow through the metal, though, if the mirror is pressed against the metal carrier.
I think that I will attach the new mirror, whether first or second surface, with the double side tape.

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PostPosted: Fri Apr 20, 2018 12:42 am 
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Hobbyst46 wrote:
. . . I think that I will attach the new mirror, whether first or second surface, with the double side tape.


Many double-stick tapes use an adhesive that won't stand up to heat. Typical ratings are for a max of 150F or 200F -- and old tungsten or halogen units will often get hotter than that.

You might want to experiment with your chosen tape and a heat gun first -- or look up the adhesive if the manufacturer provides a spec. Alternatively, McMaster Carr and others sell higher temperature double stick tapes (variously good to 250F, 300F, top around 500F).


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PostPosted: Fri Apr 20, 2018 8:05 am 
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PeteM wrote:
Hobbyst46 wrote:
. . . I think that I will attach the new mirror, whether first or second surface, with the double side tape.


Many double-stick tapes use an adhesive that won't stand up to heat. Typical ratings are for a max of 150F or 200F -- and old tungsten or halogen units will often get hotter than that.

You might want to experiment with your chosen tape and a heat gun first -- or look up the adhesive if the manufacturer provides a spec. Alternatively, McMaster Carr and others sell higher temperature double stick tapes (variously good to 250F, 300F, top around 500F).

Thanks PeteM for this important comment.
Since the old mirror was defective, I already replaced it with a new second-surface mirror (at least until I get the first-surface and try it), using a No-Name double sided tape. I had been concerned about heat from the lamp, so before I installed it, I checked with a Fluke digital thermometer and a bare-bead thermocouple sensor. Placed the sensor tip inside the assembled (without mirror) field aperture unit, near the back. Turned on the 10W LED illuminator (unfortunately, no halogen...). Room temperature was 75F. The temperature inside the frame rose by about 18F, then leveled off. This is a rough measurement for sure, heat dissipation varies, and the scope stand was lying on its side, so heat losses by natural ventilation were optimal.
Heat dissipation mainly occurs via conduction through the aluminum base of the stand. I believe, that even on a very warm day (say 90F room temperature, no AC), the mirror temperature will not reach 120. Still, I will keep that in mind.

P.S. One advantage of this commercial LED illumination setup is that the multi-fin heat sink of the lamp "housing" is outside the base of the microscope, not within the space under the stand as in some home-built LED conversions. Hence, much or most of the heat created by the LED supply is dissipated outside the scope itself.

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PostPosted: Fri Apr 20, 2018 10:04 am 
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Hobbyst46 wrote:
@MicroBob:
What is "Stainless spring steel" in this connection ? all plain stainless steel sheets (thickness ~1-2mm) that I have worked on are usually somewhat springy, but can be bent and cut, especially with heavy workshop machines.


When you make stainless steel springs you use the material in pre heat treated condition, make the spring and have no heat treating afterwards. This material is also used for many other applications just because it resists permanent deformation better. The standard "V2A" 1.4301 stainless steel is quite easily bent or dented because of its comparatively small yield strenght. It would be too soft for many everyday applications.
When your mirror arrives, you can just try on a corner how it can be cut the easiest way.
I waiting for you report since this is an attractive material if the quality is good enough for our uses.


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PostPosted: Fri Apr 20, 2018 10:12 am 
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MicroBob wrote:
Hobbyst46 wrote:
@MicroBob:
What is "Stainless spring steel" in this connection ? all plain stainless steel sheets (thickness ~1-2mm) that I have worked on are usually somewhat springy, but can be bent and cut, especially with heavy workshop machines.


When you make stainless steel springs you use the material in pre heat treated condition, make the spring and have no heat treating afterwards. This material is also used for many other applications just because it resists permanent deformation better. The standard "V2A" 1.4301 stainless steel is quite easily bent or dented because of its comparatively small yield strenght. It would be too soft for many everyday applications.
When your mirror arrives, you can just try on a corner how it can be cut the easiest way.
I waiting for you report since this is an attractive material if the quality is good enough for our uses.

Thanks Bob. Found that V2A is the same is the familiar :lol: SS304 (I am used to the 304, 316 etc type numbers...).

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PostPosted: Fri Apr 20, 2018 10:36 am 
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Hi Doron,
V2A is no official naming at all but the most used name for this material here. It is named after a reseach melt from company Krupp a century ago.
In Germany the proper name would be 1.4301 according to the "Stahlschlüssel". Of cause there are other naming systems, I don't know how many. SS304 seem to be the american system. It would be interesting to see on a world map who uses what system! I would show a lot about economic relations between the countries.

Bob


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PostPosted: Wed May 16, 2018 9:54 am 
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apochronaut wrote:
Hobbyst46 wrote:
Thanks Apo' for the idea. Is well worth trying. I ordered it.
Do you recommend that I cut it on a milling machine to avoid distortion and damage to the coating, or is there another way?


Do you know anyone with a shear? Make an oversize shirt cardboard cover, tacked in at least 8 spots around the perimeter with a tiny dab of some glue.
Mark your dimensions on the cardboard + a bit for dressing. Do some tests on a waste area first. Cut with a shear and finish it with a good fine file.

Good quality hand shears should do about as good a job, if the gauge is light enough ; about up to 16, for long ones. Leave enough extra so any small deformities, can be filed or ground away, down to the finished dimension.

I guess, first see what the gauge is. From the picture, it looked to be about 16.

The first surface mirror arrived, nicely packed within a thin polymer envelope inside a soft thick cloth pouch.
It appears to be fine, reflective, and certainly large enough for three microscope illuminator mirrors, its narrowest diameter being >50mm. Thickness is 14-15 gauge or 1.5mm. There are two large flat surfaces. Because none of the edges is a straight line, cutting out a mirror for the scope means cutting all four sides. The adventure starts here.


Attachments:
mirror side.jpg
mirror side.jpg [ 47.69 KiB | Viewed 812 times ]
mirror top.jpg
mirror top.jpg [ 46.6 KiB | Viewed 812 times ]

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PostPosted: Wed May 16, 2018 1:44 pm 
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That looks promising. It is thick enough that the danger of deformation during cutting won't be too high but then it will take some energy.

Does it have a protective polymer coating of any kind? The reason I ask, is that if so I would tack a 1/2-1mm per edge oversize piece of protective thin, hard, pressed cardboard to the coating and work to that dimension, finishing with a good file. I'm not sure how you plan on cutting it....perhaps do some corner tests to determine the degree of deformation. That would determine how much oversize to make the two covers.

If it doesn't have a coating, a very thin bead of glue along each edge could seat the protective covers. The cement would be filed away anyway.


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PostPosted: Wed May 16, 2018 4:22 pm 
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apochronaut wrote:
That looks promising. It is thick enough that the danger of deformation during cutting won't be too high but then it will take some energy.

Does it have a protective polymer coating of any kind? The reason I ask, is that if so I would tack a 1/2-1mm per edge oversize piece of protective thin, hard, pressed cardboard to the coating and work to that dimension, finishing with a good file. I'm not sure how you plan on cutting it....perhaps do some corner tests to determine the degree of deformation. That would determine how much oversize to make the two covers.

If it doesn't have a coating, a very thin bead of glue along each edge could seat the protective covers. The cement would be filed away anyway.

Thanks Apochronaut. The mirror has no protective coating and is extremely sensitive to the touch, as I rapidly learnt. So the useful part of the surface must never be touched. I clamped the mirror between two flat pieces of wood and made a test 10mm long cut with a hacksaw. I used a 24 TPI blade, although a 32 TPI may be better. Anyway, the cut looks clean, no obvious deformation and no chipping off of the reflective nickel-chromium coating. I used the saw at an angle of maybe 50-70 deg to the surface. Hence maybe I can clamp it vertically in a vice.

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PostPosted: Sat May 26, 2018 3:46 pm 
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Previously, I have seen that a second surface, 3mm thick glass mirror reflected the light correctly. I painted a black dot in the center of the light collector lens (the lens in front of the bulb/LED). Looking at it through the binocular head without eyepieces, objectives and condenser (all these were removed), the dot (and the lens and end of collector tube) appeared to be centered in the reflected image. So in view of this test (suggested by MicroBob) the second surface mirror was OK. However, there are good reasons to think that the original mirror might have been first surface, so I became picky and decided to try and install a first surface mirror anyway.

Cutting, filing and fitting the first-surface dentistry stainless steel mirror took some time. I first separated the bought item into two flat plates, using a hacksaw. Used two 10x15cm, 6mm-thick plywood plates to serve as protectors against scratches and bends or twists. Sandwiched the flat metal plate between the protectors such that the pencil mark was just visible, and clamped the sandwich vertically. Then, slowly, I used a 32TPI blade hacksaw to cut along the rim of the plywood. The mirror has a dull uncoated back side. I marked a ~37x42cm rectangle on the dull side with a pencil. Then cut out the rectangle as detailed above. For a finish, I used a coarse metal file, then a fine metal file and a flat needle file to reduce the dimensions of the mirror to the required 35x40mm. I beveled one edge to fit inside the slot in the base, but that was deemed unnecessary (see below).

Interestingly, although the reflective coating is very sensitive to the touch, it adheres very well to the metal base, so cutting and filing left the coated rims practically undamaged.

To mount it in the base, I removed the previous glass mirror from the backplate: with a pen knife, removed remains of the original cork strips and the double-sided tape with the glass mirror, then attached the new first surface mirror by means of a 1mm thick double sided tape which is being sold for mirror mountings and is compatible with heat. The result is that the reflective surface is now firmly attached to the backplate, and is at about the same distance (from the light source) as was the reflective coating of the glass mirror. Accordingly, the reflective surface is not adjacent and touching the base. It is lucky that the metal mirror is only 1.6mm thick - had it been thicker, the reflective surface would be touching the base and the collector optics reflection would be off-center.

The performance of the microscope with the new first surface mirror does not show a difference in the illumination insofar, between the glass second-surface mirror and the first-surface mirror. There are no off-center effects, and BF, DF and phase contrast function correctly. I believe, though, that the first surface mirror performs better, since any parasitic reflection from the mirror has been eliminated. As a side benefit, I am more familiar with the mechanics of the scope...

And I hope that this thread may be useful to others that run into similar doubts.
Note: the reflections in the mirror in the second and third photos are of a nearby window sun shades.


Attachments:
uncoated side of mirror.jpg
uncoated side of mirror.jpg [ 146.68 KiB | Viewed 720 times ]
mirror on backplate.jpg
mirror on backplate.jpg [ 146.06 KiB | Viewed 720 times ]
mirror on backplate 2.jpg
mirror on backplate 2.jpg [ 141.46 KiB | Viewed 720 times ]
assembled.jpg
assembled.jpg [ 116.05 KiB | Viewed 720 times ]
Assembled 2.jpg
Assembled 2.jpg [ 113.13 KiB | Viewed 720 times ]

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PostPosted: Sun May 27, 2018 3:06 pm 
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Very nice job. Good that the steel was soft enough to use a hack saw on, too. Hooray for Chinese steel! It's good those things are available so cheaply and for those requiring a good first surface reflector are a good option. You even have enough material to make a few mistakes on.


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PostPosted: Mon May 28, 2018 12:08 pm 
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apochronaut wrote:
Very nice job. Good that the steel was soft enough to use a hack saw on, too. Hooray for Chinese steel! It's good those things are available so cheaply and for those requiring a good first surface reflector are a good option. You even have enough material to make a few mistakes on.

Thanks again, Apochronaut and all contributors to this post! Your comments helped me see the light at the end of the mirror! truly a fruitful brainstorming.

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PostPosted: Tue Jun 12, 2018 10:14 pm 
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Location: California
I'm kind of late to the party here, but just wanted to point out that when working on instruments like microscopes, hollow-ground screwdrivers work better than the more typical taper-ground versions. The photo below illustrates the difference:

Image

Hollow-ground screwdrivers are sometimes known as gunsmith screwdrivers and gunsmith supply stores are good places to get them. I got a set from a place called Midway, which seems to have a good selection.

https://www.midwayusa.com/product/43952 ... driver-set


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PostPosted: Tue Jun 12, 2018 10:22 pm 
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You can also reshape the tips yourself.


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PostPosted: Thu Jun 14, 2018 10:13 am 
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Quote:
The performance of the microscope with the new first surface mirror does not show a difference in the illumination insofar, between the glass second-surface mirror and the first-surface mirror. There are no off-center effects, and BF, DF and phase contrast function correctly. I believe, though, that the first surface mirror performs better, since any parasitic reflection from the mirror has been eliminated. As a side benefit, I am more familiar with the mechanics of the scope...

UPDATE: I notice an important advantage of the first-surface mirror. Previously, while the the secondary mirror was installed, the illumination seemed OK except that I could not achieve darkfield with the "D" position of my turret phase contrast condenser, no matter which objective, auxiliary lens, immersion I used. Now, with the first surface mirror in place, I do achieve darkfield up to 40X~0.7 with some tweaking of the condenser and the auxiliary lens in the path (in contrast to brightfield, where the aux lens is redundant for the 40x objective). Since darkfield illumination is very sensitive to the illumination optics in use, I attribute this change to the first surface mirror. (Hand-waving, I know.)

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