Reichert zetopan questions

[apochronaut]

Yes. That was my suggestion, that extending the 10X Chinese objective a bit would put it more in line with the 13mm focal distance requirement of your eyepieces. Very good that it works well.

The Zetopan should be able to produce a quite uniform illumination field. It was Reichert's flagship research microscope for quite a few years. Auxillary lenses in order to widen the illumination field are common with microscopes.
Do you have the Operating Manual ?

Here is a link to one https://isurplus.com.au › Zeto...PDfZetopan Research Microscope User Manual.pdf

Didn't copy correctly. The link just brings up the people hosting it not the manual.
It tops the list if you search adjusting a zetopan for kohler in google.

[wabutter]

As an addendum to apochronaut’s thread, parfocality on a Reichert Zetopan and later on the Univar/Polyvar scopes was achieved by hand honing the shoulder of the objective. This was specific to the position in the nosepiece and each scope. It was one of the reasons the objective mag position was marked on the nosepiece.
It is also one of the reasons Reichert never became a high volume microscope producer. Even in the research space.

More importantly the par-centricity was also honed to each scope to a spec of 5 microns or less from one objective to the next. That is roughly the diameter of a RBC.

Imagine being able to have a red blood cell in the middle of the field at 40x and shift to the 100x and have no movement of that cell in the field of view. That was the degree of precision that was standard in Reichert scope. That commitment to detail proved to be critical to the semiconductor industry when geometries moved toward 1 micron and Reichert dominated the semiconductor microscope market.

[Lukas]

Hi,

Thanks for the link, but I've already collected quite a bit info, including a phase contrast manual, and even printed all that stuff. While tossing around the internet I've found a quite valuable collection about optics of microscopes. it's quite a good explanation, also including limitations of DF patch stops, what types of dark field condensers are and so on :
https://wp.optics.arizona.edu/jgreivenk ... 1/ch23.pdf

In general, I must admit, the experiments ended like this : using DF patch stops with 10x/0.25 objective works really well. In case of 25x/0.45 the background is not as dark; but still not bad overall. I the paper above possible reasons are explained. Above that it's possible to push it with with a big stop disc even to 40x/0.65 but the quality is very bad and not useable at all.

Also I did some experiments while trying to fit a lens between the condenser and light source, in an attempt to increase illuminated area. To my big surprise, one of them worked. It's a chinese photo adapter. In this way it's possible to use 4x objective. For larger magnifications the lens adapter should be taken off, I think.

Another weird thing I encounter is this. Lets say, a phase disc is used as a DF patch stop. Then, while watching through eye pieces, the background is dark red. But the camera always sees background being black. What sort of mystery is that ?

Regards,
Lukas.

[Hobbyst46]

In general, I must admit, the experiments ended like this : using DF patch stops with 10x/0.25 objective works really well. In case of 25x/0.45 the background is not as dark; but still not bad overall. I the paper above possible reasons are explained. Above that it's possible to push it with with a big stop disc even to 40x/0.65 but the quality is very bad and not useable at all.

Good DF at medium to high NA is exceedingly sensitive to the size of the patch stop, its coaxial with the objective and condenser, and its distance from the specimen. It is very difficult to achieve such accuracy without precision mechanics of the system. The Ph3 phase contrast condenser annulus (for the 63X and 100X objectives) does it quite well for NA=0.2-0.4 on my microscope.

Also I did some experiments while trying to fit a lens between the condenser and light source, in an attempt to increase illuminated area. To my big surprise, one of them worked. It's a chinese photo adapter. In this way it's possible to use 4x objective. For larger magnifications the lens adapter should be taken off, I think.

Not surprising. I have various thin convex magnifier glasses, the remains of "for parts" broken old instruments; several of them do this trick, of increasing the illuminated area even for the 2.5X objective. Only that they are not optimized for focus uniformity across the field of view, spatial and color aberrations.

[apochronaut]

On later instruments with infinity corrected optics the 1.25 abbe aspheric has a wide enough angle to fill the field of a 4X. The aux. lens used for 2.5 X has quite a severe hemisphere, which faces up.

[Lukas]

Hi,

While being lost at number of different settings I did compile the following table. General observation with this microscope is, that with magnifications up to and including 25x auxiliary lens might improve evenness of illumination depending on settings. Tests were carried out with a camera connected to computer monitor, sometimes taking pictures and comparing A/B if difference is not immediately apparent. Note that field of view of the camera is quite large and edges extend outside FOV of eye pieces a little.

Regards,
Lukas.

[Lukas]

There are parfocalizing shims available, in incremental thicknesses. They come in a group of standard thicknesses, which you then add together to get in between thicknesses. An option if your plumbing tape method gives out eventually. With lower magnification objectives, altering the tube length is not without an effect on the optical quality.

Historical note.
Some old school monocular microscopes right up until the late 40's had a graduated adjustable draw tube so one could use objectives that required a specific tube length and intermediate image location, and then the user could set the optical tube at that length. That is one of the reasons that monocular microscopes persisted so long after binocular versions had become very common. It wasn't uncommon for microscopists to have an array of specialized objectives of various parfocal measures, made by various makers. An adjustable drawtube and sometimes a different eyepiece allowed for the use of any of them. Spencer went so far as to custom manufacture objectives of various parfocal lengths. While their standard was 34mm parfocal, they also made quite a few objectives to the 36 2/3mm Bausch & Lomb standard and I have even come across a 4mm 44X .85 fluorite that is 32mm parfocal, obviously intended to be used in the same nosepiece with Zeiss objectives or in a Zeiss microscope. Presumably, the intermediate image distance was the 13mm of Zeiss rather than the 11mm of Spencer.

Hi,

Eventually, the plumbing tape has given up, so a more permanent solution was necessary. Searching for parfocalizing shims on internet ended with no results. So, plastic properties of steel wire were exploited and it was cold worked by using a hammer. The wire was first flattened, then bent into a circle and cut in the middle. Resulting washer was hammered again while checking for uniform thickness via caliper. In this way, both parfocality and par-centering was achieved and the solution is permanent.

By the way, a couple of months ago I also purchased a microscope for my daughter. It was of chinese types but not the cheapest of all. And there was a draw tube inside, of which the main purpose was the ability to draw the eye piece out. This resulted in in increased magnification, so the manufacturer could now advertise their microscope as magnifying 1240 times instead of mere 400. Of course, this made no sense, since even at 400x the resolution was not good at all.

Regards,
Lukas.

[BramHuntingNematodes]

Ah yes the engineers vise.and square-faced cross peen hammer classic optical bench equipment

[apochronaut]

Hey. I've got one of those 15mm objectives with the square 1/2" mount just like yours as well!


Good job on the shim.

[Lukas]

I figured for 69.00 + shipping you could get it up and running. The sleeve size will be correct for Reichert but you might just check with the seller and measure it. You can drop your condenser out of the Akehurst slide and measure it. I can't remember what the Reichert sleeve diameter is.

The Zetopan used an Akehurst Slide type of condenser mounting system but the condenser itself has a sleeve mount, which fits into the Akehurst Slide. No doubt other Reichert models used a plain sleeve fitting and it would be unusual for Reichert to use different sleeves, since DF condensers are optically universal.

The ebay condenser has the capacity to work on your microscope but you would either have to remove your BF condenser from it's alide and put the DF one in or find a spare Akehurst slide for a Reichert somewhere.

Since you posted a catalogue image from Reichert. The two condensers pictured in the cat. image are the same in function but 9 99 00 18 has in addition a toric lens in the bottom which broadens the field projected by the condenser. It would work for 10X objectives and up. The model 9 99 00 03 would cover the field of objectives only 25X and up likely but maybe only 40X and up. I haven't used that one but I have used a 9 99 00 18 .
The field coverage of a DF condenser( any condenser) is dependant on the f.o.v. of the eyepieces as well. I have used a DF condenser similar to 9 99 00 03, which was good from 25X objectives to 100X with a 20mm f.o.v. but if the f.o.v. was closed down to 18mm, it's function could be brought down as far as a 20X objective.

When using iris diaphragms to get DF you don't want to close the diaphragm any more than about 1/3 of the diameter. For instance with a 1.25 N.A. objective the diaphragm would be closed to between .80 and .90.

Hi,

Not long ago I've bought this condenser. The surface was a little bit rusty, but optical surfaces were intact. On the bottom side the condenser has a stop in the middle.
After receiving the item it has became apparent that it would not fit in as-is. Centering knobs were disallowing the condenser to be inserted. That was sorted out by simply removing them.
Yet the image was very faint. The 100W 3600 lumens halogen was not illuminating it properly, so it became apparent that something is wrong. While viewing with less magnification I saw unfocused blob of light with center even darker.
Is it so that light from illuminator is focused by a DF condenser in such a way that it's distance from the light source is important ?

However I did not give up so easily, and started experimentation if any sort of lens would help with that. After trying maybe 10 different specimen one particular lens was found to work. It was a bottom lens of an old eye piece.
So, the condenser was ready to get a DIY mount with eye piece lens with it's tube on the bottom.
After that it seems to work quite well. Useable range is from 20x/25x to 63x/0.8 and up to 100x/1.3 oil with iris closed half the way.
Comparing with a dry condenser, image is a little bit cleaner and sharper, also color is more white, so I'm assuming it should be working as archromatic.
Interesting observation is that opening or closing illumination field diaphragm also changes the size of working area for D.F., I guess that should work in this way.
After testing all of this it became apparent that with DF illumination objective's (un)corrections are far more apparent. Original Reichert achromats are unfortunately no longer good enough =.
According to specifications short barrel olympus objectives should work, but so far 20x plan apo seems to unobtainium. Any suggestions ?

Regards,
Lukas.