BFP1 latch on the Olympus DIC slider(s)

Everything relating to microscopy hardware: Objectives, eyepieces, lamps and more.
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BFP1 latch on the Olympus DIC slider(s)

#1 Post by Macro_Cosmos » Thu Jan 19, 2023 12:17 am

I have a UApo N 40x objective that asks for the BFP1 latch, thus officially incompatible with the normal U-DICT sliders. People often claim there is no difference between DICT and DICTS, I will demonstrate the opposite.
BFP stands for back focal plane. Most UIS2 objectives have a BFP of either -19.1 or -25. There are several exceptions and they require special condenser prisms, usually. I will ignore those. Olympus' objective selector will show this if you are interested.

Full resolution: ... d562_o.png
- Normal position appears darker but background is uneven
- Colour variance
- Intensity variance
- With the BFP1 latch engaged, the image can be made very dark by engaging the translation knob. The normal position will always showcase a weird bright spot.
- Only applicable to this specific objective/prism combination. Others may see a more/less prone effect.

Full resolution: ... 7745_o.png

Here is an animated illustration for the valve.
bfp12.gif (122.45 KiB) Viewed 1178 times
The BFP1 slider ensures that the extraordinary and ordinary waves split by the condenser prism gets combined correctly. It lowers the prism by around 6mm.
Is there a difference? Clearly, yes.
Does it matter? Probably not, background can be replaced/cleaned. The minute intensity difference/unevenness is hardly noticeable.
Does it depend on the objective? Likely, the effect could be more or less prone, but this is just a guess.


neal Shields
Posts: 57
Joined: Sat Jun 04, 2022 8:02 pm

Re: BFP1 latch on the Olympus DIC slider(s)

#2 Post by neal Shields » Thu Feb 09, 2023 10:18 pm

"It lowers the prism"

I don't have the U-DICTs. I have the "normal" U-dict.

From the photos of the slider on the internet it seems that Olympus has removed the thick removable analyzer and replaced it with a thin filter.

I assumed that this was to create room to move the prism up, not down.

Can you confirm that from "normal" to BFD1 the prism is lowered?

I assumed that the BFD was measured as increasing negative numbers from the flange. Where distance like parafocal distance was positive numbers from the flange to the front focus) That a BFD of -25 was 6mm closer to the eyepiece than the -19.

If that is the case than I should get the same result by spacing the objective down 6mm. I did that ($10 spacer from china) and probably duplicated your results although my photography isn't as good as yours.

As a result of my experiment I have concluded that it definitely (as a hobbyist) doesn't make sense for me to buy a U-DiCTS and sell my U-DICT which would be a lot of trouble and cost. (There is about a $400 difference on eBay)

I have also decided that I am not even going to leave the spacer on my lens (I also have the UAPO340 40x water).

Also I have read somewhere that the "best" DIC setting is right before the black stripe and I don't think there is nearly as much noticeable difference there.

I can understand that a laboratory that is dealing with human lives and peer reviewed research has to have it "right" but I can't justify the expense.

(Note: I also took my standard -19 BFD 40x UplanFl and spaced it down. Still no noticeable difference.)

neal Shields
Posts: 57
Joined: Sat Jun 04, 2022 8:02 pm

Re: BFP1 latch on the Olympus DIC slider(s)

#3 Post by neal Shields » Mon Feb 27, 2023 8:45 pm

I figured it out, I think.

According to an Olympus manual I found online for an IX81 my UAPO340 objective can be used with either a U-DICT or a U-DICTS slider.

The difference they show is:

U-DICT "The background interference color is continuously variable from gray sensitive color to purple sensitive color"

U-DICTS "The background interference color is continuously variable from black to light gray"

Further I now believe that the "normal" position on the U-DICTS slider is the uppermost because it is expected to be used with an inverted microscope so up will be closer to the objective I.E. -19 and down will be farther from the objective I.E. -25

This was confusing me because the only position on the U-DICT is the lowest position with the U-ANT taking up the space above it.

Solve one problem and another crops up. The same instruction manual that says my lens is compatible with the U-DICT also recommends (demands) that I use a lower prism DPAO40 instead of the DP40 I have.

However one other site on the internet says I only need the DPAO40 for the UAPO340 oil, not water.

After looking at a picture on this site that shows both the DP40 and DPAO40 side by side it seems the difference is a larger aperture to account for a larger NA. The oil lens has an NA of 1.4!

My lens is probably borderline between the two at an NA of 1.15 but I get excellent results and in addition I don't have the rare and very expensive TLO condenser swing in lens, so my working objective aperture is somewhere between the objectives NA of 1.15 and the condenser aperture of .9. So I suspect I couldn't get any benefit from the DPAO40 without also buying a TLO condenser lens.

As it stands I love the UAPO340 for pond water. The difference between it and my UPLAN FL PH 40x dry is striking. Like B&W to Technicolor when there is water between the sample and the cover slip.

However, with a Diatomlab test slide where the diatom is in contact with the cover slip, I can not detect ANY difference between the two lenses.

This is a link to the instructions I am referencing: ... manual.pdf

Thanks for everyone's help and input.


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