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Strange problem with a DIC setup on a Olympus BH-2
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Clemmys



Joined: 16 Jul 2015
Posts: 10
Location: United States

PostPosted: Tue Jul 28, 2015 2:58 pm    Post subject: Strange problem with a DIC setup on a Olympus BH-2 Reply with quote

Please excuse any terminology issues, I have a background in microbiology but have never used a scope with a DIC setup before now.

I bought a Nomarski condenser and intermediate tube off of ebay to use with my BH-2, but unfortunately discovered after the fact that it was made for the BH/CH2 series (different condenser attachment), so I haven't been able to use it. Before I could pick up a BH or CH2 to try it with, I ran across a good deal on another BH-2 with a DIC setup already installed from an auction house, including a few interesting objectives that I wanted to try, so I picked that up instead.

However something seems to be wrong with the BH2-NA slider (or analyzer) that came with the full setup. I spent a frustrating hour or 2 trying to get DIC working and all I could get was a rainbow pattern no matter what adjustments I made. It was then that I remembered my older DIC setup that shares a similar slider/analyzer. I swapped the two parts (newer bh2 model to the old slider/analyzer) and bam, instant DIC effect.





Holding the Intermediate tubes (with analyzers) at the same angle in front of my polarized LCD monitor you can clearly see that something different is going on. Not sure what it means, but the newer one doesn't create the same black lines when held at the same angle in front of the polarized light source. The knob on the analyzer turns smoothly with the newer setup, but all it does is move the rainbow across the field of view.
Any ideas would be appreciated=)


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g4lab



Joined: 23 May 2008
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PostPosted: Wed Jul 29, 2015 12:35 am    Post subject: Reply with quote

The spacing demonstrates the different angles and orders of interference colors of the sliders. I think you may have your sliders mismatched with the
the DIC prism on the condenser. or something like that.

The sliders have Wollason prisms in them and the angles used depend on the mag an NA of the lens to be matched to.
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Pau
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Joined: 20 Jan 2010
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PostPosted: Wed Jul 29, 2015 1:21 am    Post subject: Reply with quote

Hi Clemmys, welcome aboard

I'm pretty sure that your problem is the wrong orientation of the optical components: in your last image you can see two black lines and you need to see just one in the center (when no shear is set, hence the field is black)

Two posible causes:
1. wrong polarizers orientation. Be sure that the condenser polarizer is oriented E-W and the analizer (if not built in the objective prism) N-S

2. wrong orientation of the objective prism slider. Try putting it at the opposite orientation, at 45º of the microscope but at the opposite sense, for example rotating 180º the intermediate piece that holds it

Maybe your condenser or objective prism slider cames from an inverted microscope where the prisms orientation is different.

If you post pictures of the equipment one of our several Oly DIC experts will give you more precise advice.
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Clemmys



Joined: 16 Jul 2015
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PostPosted: Wed Jul 29, 2015 7:50 am    Post subject: Reply with quote

Thanks for the welcome and replies=)

Orientation of polarizers: the condenser polarizer only has an approx 10 degree range of adjustment once you slide it into position, so no chance for me to really screw that up. (believe it is the BH2-NC, not the 'universal' condenser with interchangeable prisms) The analyzers - both of them are attached so that the red dot is aligned with the one the scope. I did try slowly moving the intermediate tube holding the analyzer around 360 degrees and testing it in different positions and that did not work.

"Old" NIC setup (cannot test the condenser since it is for a BH/CH2. Analyzer works with the "new" setup


"New" setup with defective? analyzer


"New" analyzer installed


"New" condenser installed


"Old" analyzer installed
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Clemmys



Joined: 16 Jul 2015
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PostPosted: Wed Jul 29, 2015 8:02 am    Post subject: Reply with quote

Pau wrote:

I'm pretty sure that your problem is the wrong orientation of the optical components: in your last image you can see two black lines and you need to see just one in the center (when no shear is set, hence the field is black)

Two posible causes:
1. wrong polarizers orientation. Be sure that the condenser polarizer is oriented E-W and the analizer (if not built in the objective prism) N-S

2. wrong orientation of the objective prism slider. Try putting it at the opposite orientation, at 45º of the microscope but at the opposite sense, for example rotating 180º the intermediate piece that holds it

.


Forgot to answer directly - The strange thing is that the analyzer that has the two black lines is the one that works. It is possible that I am not holding it perfectly square to the screen when I see 2 lines, because it does not take much of a shift to get a central black line with a second line just touching the outside edge.

1 - analyzers are installed correctly I believe, pictures are above to confirm any mistakes on my part=)
2 - I did try spinning the intermediate tube around 360 deg, but never could find a point that 'worked'. Where the dots line up got the darkest, but I get that weird rainbow effect (all colors, not just a slight gradient) with 0 to minimal DIC effect across the field.
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Pau
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PostPosted: Wed Jul 29, 2015 8:24 am    Post subject: Reply with quote

I was just writing: Just try to mount the "new" slider in the oposite sense, maybe it can be just mounted from the rear left position of the intermediate piece or just turn the intermediate piece, even if it doesn't lock at a precise position you can easily find the adequate one. It seems that you've already done it, so I have not more clues.

You can also try to combine the new and old intermediate pieces and sliders, but I don't think it could solve the issue.

I use a hybrid dic setup with components from different makers. I can combine the DIC Zeiss condenser both with an original Zeiss slider or with an Olympus one and both work but mounted at the opposite senses (Zeiss NW-->SE and Oly SW-->NE). Maybe the new condenser prisms are mounted at inverse position of the old ones. I don't know enough about Oly condensers but i some models the position of the DIC prisms can be changed, but is seems less risky to just change the orientation of the DIC objective slider.

Could you post pictures of the sliders between crossed polarizers to see how the color lines compare? (for exemple without objective, sample and condenser prism)
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g4lab



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PostPosted: Wed Jul 29, 2015 9:09 am    Post subject: Reply with quote

The "Polarizer" in the condenser is not just a polarizer. It also has a Wollaston prism in it which has a range of objective sliders it should work with. (In the Zeiss INKO system the polarizer looking disk is labeled with the Roman numerals I II or III to determine the range which is marked on the objective sliders. This is what engenders the "differential interference".

If the ranges of the Wollaston prisms are not matched properly you will have lots of color.

If you examine the sliders and "polarizer" between crossed polars you will see the order bands but without the color caused by mismatch.

Zeiss used to have generalized sliders labeled I II III for the objective side too. But more recently they make sliders specific to each objective but they still have a label to tell you which prism to use on the condenser side.

If anybody needs newer Zeiss sliders I have access to quite an assortment.
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Pau
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PostPosted: Wed Jul 29, 2015 9:39 am    Post subject: Reply with quote

g4lab wrote:
The "Polarizer" in the condenser is not just a polarizer. It also has a Wollaston prism in it which has a range of objective sliders it should work with...


Gene, I find the above sentence misleading: At least with Olympus and older Zeiss systems the condenser polarizer is just a linear polarizer positioned under the condenser, in fact it can be used for simple cross pol work. The condenser DIC prisms are placed at the condenser turret.
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Clemmys



Joined: 16 Jul 2015
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PostPosted: Wed Jul 29, 2015 9:50 am    Post subject: Reply with quote

Pau wrote:


You can also try to combine the new and old intermediate pieces and sliders, but I don't think it could solve the issue.

Could you post pictures of the sliders between crossed polarizers to see how the color lines compare? (for exemple without objective, sample and condenser prism)


Can't get the slider out of the 'old' intermediate tube to intermix or examine more closely. Will follow with some pics of the new slider.

No objective, sample, condenser set to brightfield, but polarizers left in place. First row is "new" analyzer with the first pic of the adj knob screwed all the way in, then 1/2 way out, then all the way out. Second row is the 'old' analyzer (that works for me) (need to clean my sensor or something in my light pathway...)


I took opened up the analyzer for the 'new' NIC. It appears that the prism has not been glued down flush to the metal ramp. Glue is under the glass, particularly on the right side, which changes the angle of the prism. Could this be what is throwing things off? (it is not loose - the glue is holding it firmly)




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Pau
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PostPosted: Wed Jul 29, 2015 10:08 am    Post subject: Reply with quote

Clemmys wrote:
No objective, sample, condenser set to brightfield, but polarizers left in place. First row is "new" analyzer with the first pic of the adj knob screwed all the way in, then 1/2 way out, then all the way out. Second row is the 'old' analyzer (that works for me) (need to clean my sensor or something in my light pathway...)


Sorry, now I understand nothing: the first row of images looks right, like a DIC prism must look between crossed polarizers (well, the right one with the black band more centered) while the lower row looks weird.

Test if the optical orientation of the condenser prisms do match the slider prism. You can do it with the microscope full mounted looking at the back focal plane with a phase telescope eyepiece or just removing one eyepiece

Clemmys wrote:
I took opened up the analyzer for the 'new' NIC. It appears that the prism has not been glued down flush to the metal ramp. Glue is under the glass, particularly on the right side, which changes the angle of the prism. Could this be what is throwing things off? (it is not loose - the glue is holding it firmly)


Don't touch the prism, they are very delicate. The angled position could be to prevent reflections.
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g4lab



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PostPosted: Wed Jul 29, 2015 10:54 am    Post subject: Reply with quote

Quote:
Gene, I find the above sentence misleading: At least with Olympus and older Zeiss systems the condenser polarizer is just a linear polarizer positioned under the condenser, in fact it can be used for simple cross pol work. The condenser DIC prisms are placed at the condenser turret.


Actually I spoke imprecisely. It depends on the age of the system and what I was thinking of while posting was newer systems, which have the condenser prisms and polarizers combined and they drop into a turret. The older ones did separate the prisms and the polarizer.

I have not played much with Oly componentry. But pretty many Zeiss systems of varying ages.
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Clemmys



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PostPosted: Wed Jul 29, 2015 11:36 am    Post subject: Reply with quote

I would think the prism would be attached to the precisely machined angle of the slider. By having the glue under it, it changes the angle of the glass a couple of degrees.

Yes, this setup has the linear polarizer under the condenser that slides into place. The different DIC prisms are rotated into position (can choose between 10, 20, 40, and 100x with the 'new' setup, the older setup leaves out the 20x prism slot and has an extra phase slot).

Pics of the 'new' analyzer with a 10x splan apo, focused on an empty slide, polarizers in place but condenser set to brightfield. pic taken through missing eyepiece hole. (adj knob fully screwed in) I can't get the typical black line


adj knob screwed out 1/2 way


adj knob all the way out


with the old analyzer, I can get the black line, but strangely I can't take a picture of what I see (comes out as a flat field of monotone)
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David Maitland



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PostPosted: Sat Aug 01, 2015 8:34 am    Post subject: Reply with quote

Hello – I am thinking that perhaps you cannot use DIC equipment on a BH2-BHTU stand… (the stand you have in your pictures). The BHTU stand is in the Olympus “affordable” range (which can be translated to mean that there are compromises with what it can do) -Importantly, it has a fixed nosepiece with built-in optics set into it. I am guessing that it is this lens system that is throwing off the DIC function (there are no extra optics in either the BH stand or BH2-BHS or BHT stands). Also, If you look at the brochure for the BH2-BHTU stand here:

http://www.alanwood.net/downloads/olympus-bh-2-bhtu-brochure.pdf
you will see that the DIC condenser and slider are not included, and the brochure makes no mention that DIC is possible with this stand – but somebody else here might know differently….

I do not think there is anything wrong with either of your DIC kits and the problem is not to do with incorrect orientation of components. Also, the DIC prism in the slider is purposely set at a slight angle in order to avoid reflections as light passes through the prism (do not attempt to “flatten” it out!

The DIC effect you are getting is not correct with either “set” on your BHTU stand – you should be able to get a nice even colour across the entire frame which you are not getting (the blue and grey have a clear gradient in your pics).

Instead, try to get hold of an old BHA stand or a BH2-BHS stand – both of these have the better 100w lamp-house and allow use of all techniques (I would recommend selling the BH set and hold onto the more recent dovetail fitting set to fund your BHS acquisition – you can also sell the BHTU stand for that matter if you settle for a BHS).
Hope this helps.
David
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Clemmys



Joined: 16 Jul 2015
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PostPosted: Sat Aug 01, 2015 11:49 am    Post subject: Reply with quote

- Perhaps, but as I understand it the BHTU is the same as the BHT, but with the different nosepiece (non-removeable and different angle). It doesn't change the light pathway, and the components still attach to the modular system??

- I realize that the prism is supposed to be at an angle in the slider. The point I was trying to make (poorly) is that the angle seems to be slightly off since the glass prism is not glued down flush to the angled ramp. Glue under the right side in particular makes the angle more than it would be if it was flush to the metal..

- DIC effect not correct on either set - this is my first time using it so I will have to defer on that. I have seen pictures online with slight gradients. I definitely can not adjust it so that there is 0 gradient.

- I might end up picking up a BHS stand just for the removable nosepiece. (and try out your theory). I like the flip forward style of the BHTU nosepiece, but my objective collection has been growing..
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Pau
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PostPosted: Sat Aug 01, 2015 12:34 pm    Post subject: Reply with quote

Clemmys wrote:
- Perhaps, but as I understand it the BHTU is the same as the BHT, but with the different nosepiece (non-removeable and different angle). It doesn't change the light pathway, and the components still attach to the modular system??

...

- I might end up picking up a BHS stand just for the removable nosepiece. (and try out your theory). I like the flip forward style of the BHTU nosepiece, but my objective collection has been growing..


In fact David's post has much sense for this kind of DIC systems where a common objective Nomarski prism must be placed at the precise distance of the objective to image its interference bands at the rear focal plane.
In th BHTU this distance is greater than in BH stands because the inverted nosepiece. I ignore up to what point the built in lens could compensate it.
(but this couldn't explain the weird apparence of your DIC slider when imaged alone without objective and condenser prism)

A BHS stand is a good idea, in fact you can get more money selling your surplus DIC components
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