Nikon Diaphot TMD w/ DIC -- Help!

[KurtM]

I am reasonably knowledgeable and experienced in microscopy, started in 2008 with a Spencer Model 13 and No. 735 research lamp learning to set up Kohler the old fashioned way. I have been using a Zeiss WL with DIC as my workhorse stand since 2015, and have just obtained a Nikon Diaphot TMD with phase and DIC. I downloaded TMD user and DIC manual PDFs from the web.

I immediately noticed differences between what the DIC manual illustrates, and what I have, and ran into trouble attempting to achieve Kohler, all of which which led me to realize the DIC arrangement on my scope is ... well, different.

Basically, it goes like this: the one illustrated in the TMD DIC manual has both combining prism and POL analyzer in a single module that fits into (what I call) the cube position under the nosepiece. The other, what I have, provides two modules: the one in the cube slot contains just the POL analyzer, and the combining prism is in a slider housed in a different style nosepiece that appears specially made for it. Here are two overall images; the first is what I have, and the second the single-module version as depicted in the manual:




Note that the stage is positioned considerably higher on mine, in the top image, due to the added nosepiece height for accommodation of the DIC combining prism. I'm thinking this is a clue as why I cannot get the lamp iris to focus: the condenser cannot go high enough to compensate for the additional nosepiece height.

I have been able to find nothing on this, and hope somebody here can help me understand this very new-to-me equipment. I am also inexperienced with LWD condensers and objectives, although I understand setting up Kohler should be no different.

Here are a couple close-up images of my scope, as it sits on my bench right now:




I don't even know if this is a factory thing, or somebody's "Frankenscope"? I'm getting decent images, and am delighted with my "new" Diaphot generally, but I really need to get to the bottom of why Kohler seems impossible -- and I'm stumped!

Thanks!

[KurtM]

Update: Long story short, I lowered the stage as much as I can and still focus my objectives, also coaxed the condenser arm up to the very tip-top of its travel range (past an obstruction I uncovered, that prevented it before), can now focus the lamp iris. But since it is such a stretch to make it happen, I'm still eager to know exactly what Nikon had in mind - the adjustments seem a bit extreme.

PS: I never really thought it possible this is a Frankenscope, all the bits look a little too refined for it to be possible, just said it to see if I could stir up some action.

[Cactusdave]

Yes this scope has certainly been modified from the configuration of a standard Diaphot TMD with DIC. The standard configuration is as shown in your second photo and is identical with my microscope.

The black box rather crudely attached with screws below the objective turret, with the pull/rotate rod with the letters on it is definitely non standard and MAY be the source of your Koehler setup issue. I don't know what it is for sure, but I'd guess it's from an in house conversion to incident (epi) fluorescence. If that's so the incident lamp house would have projected out the back of the stand and has been removed. Is there a hole in the back of the stand where it would have fitted? If I'm right then the black box covers the fluorescence excitation filter changer operated by the rod. Have you tried pulling out the rod as far as it will go which MIGHT remove all filters from the path and solve your problem? In any case I would be inclined to carefully remove the black box and see what's under it. It may be there's something that can be removed from the light path and it would be helpful to know what's there. I'm assuming the DIC combining prism is now on the slider immediately above the black box, and it can be removed from the light path by pulling the silver knob on the slider. This would also be useful to know for sure, if you want to use the microscope for bright field or simple polarisation when you don't want the combining prism in the light path.

Hope these ideas help.

David

[KurtM]

Oh good, I was hoping you'd turn up. I have made much progress since first posting so let me update a little. I can now achieve Kohler without difficulty. The black box isn't a box at all, but a pair of easily removable (no tools) dust covers. For the first image below, one of the covers has been removed and set aside to reveal the POL slider beneath. The POL slider has click stops, and you can see an indent in the dovetail just as it emerges. In this shot POL is out of the light path.

DIC combining prism is in the top slider (with silver knob), works perfectly with click stops for in and out positions, slider removes altogether and reinstalls easily. Brightfield or simple POL is readily achieved, it all works very nicely, actually.



Below: POL slider and both dust covers removed. Slider pops right out, slides back in easy enough.



Below: POL cassette removed from POL slider.



Below: A look back at the cube space with POL slider removed.



This arrangement looks OEM to me, and at least isn't utterly unique, see here:

http://scopeoptic.com/nikon-tmd-inverte ... -contrast/

[Cactusdave]

Firstly I'm glad you've sorted out your Koehler issue and are generally happy with the microscope. I love mine, it's very versatile. The only downside is the relatively low NA of the condenser (0.52) which limits somewhat the performance of high NA objectives.

Looking at what was under the black box, and also the sales blurb for the similarly modified Diaphot that you found, it does seem the slider block in there was designed to house not just the analyser for the DIC setup but also an excitation filter block for epi fluorescence. All that has been removed just leaving you with the necessary analyser and an otherwise empty block.

What was causing the Koehler issue BTW? It would be interesting to know.

David

[KurtM]

What was causing the Koehler issue BTW? It would be interesting to know.

Turned out there was a piece of debris fouling the rack, and I had assumed it was a limit stop. After clearing it, I am able to adjust the condenser as required. Gotta love those simple fixes, I was well on my way to drilling and tapping new dovetail mounting holes if necessary when I discovered it was only trash in the works.

I was also thinking my DIC arrangement (versus the one you have) might have something to do with fluorescence compatibility. I really don't understand how epi fluorescence in our microscopes works well enough to get much further than that, however.

[Cactusdave]

Glad it's all working well now. I'm sure that at one point this microscope had an OEM conversion to epi fluorescence, but all gear that was stripped out before the microscope was sold on. The Diaphot TMD is a great classic IMO and retains its resale value far better than many other microscopes of similar vintage because it's so versatile and still a valid lab tool.
David

[KurtM]

Getting into some Nikon Diaphot TMD "trivia" here, but I want to understand some finer points just out of curiosity...

As established above, there are evidently two different DIC arrangements for the Diaphot TMD, whereas one provides POL filter and combining prism in a single slider under the nosepiece, which is what Cactusdave has the manual shows, and the other provides POL and prism in separate sliders, which is what I have, as shown in detail photos above. My arrangement, then, has a modified nosepiece with provision for the prism slider, which makes it stand noticeably taller (compare first and second photos in this thread).

What I'm wondering now is:

1. Which is the earlier, and later, arrangement?

2. How is the combining prism removed from the light path in the single slider? I take it the larger wheel on the slider marked "In-Out" flips it 90 degrees? And the smaller coaxial knob adjusts the prism laterally?

3. There appears to be a slider under the coaxial knobs which I assume is a POL slider?

Thank you ... and now back to your regularly scheduled programming...

[mtuell]

Kurt,

Well, thanks for the info! I've actually got one of those 20 mm extenders that hold the slider. It came with a fluorescence scope. Now that is starting to make some sense!

As for your questions - #1, I'm not sure - it may be that they are of the same vintage, but one was if you also wanted to do fluorescence. The arrangement I've got for DIC will definitely preclude EF.

#2 If you are referring to the other setup, like the one I've got - yes, I think you've got it exactly right. There is also an analyzer below the prism, which is your question #3.

Mike

[ldflan]

Hi Kurt.

I just acquired a Diaphot with your DIC arrangement at a very reasonable price. I also have the more usual version, so I am going to do some comparisons of results.

It seems pretty clear that this arrangement with separate prism and polarizer sliders below the objective turret is one that is designed to allow the operator to very quickly switch from a transmitted DIC image to an epifluorescent image of the same specimen. There are many applications where this is quite useful. Since it's rare, and poses some potential problems along with its advantages, I imagine it's something that was developed as a later accessory to be added if needed.

I suspect that this arrangement with separate sliders is probably an afterthought because it adds 21.5mm in height to the base of the objective turret, as noted above. In effect, it is converting a microscope of 160mm mechanical tube length to a 181.5mm mechanical tube length scope. There is no corrective lens in the accessory piece for the prism slider. I see no indication of a corrective lens coupled with the prism, either. The eyepieces are standard Nikon CFWN 10x/20s. The stage accommodates the additional turret height by the simple expedient of being clamped 20mm or so higher than normal.

It may be that this tube length increase is not very important, especially at magnifications of maybe 20x and up? The well-known Leitz memo from the mid 1970s regarding their shift from 170mm TL to 160mm TL objectives suggests that the difference in objective performance when using a 160TL objective on a 170TL scope is minimal with objective powers of 16x and above. And it notes that there is +/- 10mm of play in tube length on any binocular scope having an adjustable inter-ocular distance for the eyepieces.

Here the difference in the position of the intermediate image created by the tube length discrepancy is probably more because the objective focal length discrepancy is greater (181/160 instead of 170/160). I certainly do not know enough to say how much more the difference is. At a total guess, I am wondering whether magnifications of 20x and below might suffer from the increased tube length, so I may do some comparative tests.

The Nikon Diaphot DIC system includes a prism for 10x objectives, so Nikon must have thought the performance at that magnification is acceptable, even with the added mechanical tube length.

It might be interesting to try some Leitz 170TL mid to low power objectives on the Diaphot in this configuration, just to see whether they perform better than 160TL objectives.

[Given the NA .52 limit of the Nikon DIC LWD condenser, and given the likely need/desire to use LWD objectives, high magnification objectives are of limited usefulness on the standard Diaphot. Accordingly, the Diaphot DIC condenser has prisms for 10x, 20x and 40x. (It is possible to "hot rod" the Diaphot using Diaphot 200/300 condensers and prisms to accomplish good DIC imaging at high magnifications at NA of up to 1.4; the later series condensers include an NA .85 LWD dry condenser, oil/water/glycerin condensers, etc., all of which can be used with more or less ease on the Diaphot, with slight modifications of the mount orientating pin.)]

1. Which is the earlier, and later, arrangement?

No idea. I am guessing the second arrangement with separate prism and polarizer slider is later, for reasons explained above.

2. How is the combining prism removed from the light path in the single slider? I take it the larger wheel on the slider marked "In-Out" flips it 90 degrees? And the smaller coaxial knob adjusts the prism laterally?

Yes, precisely.

3. There appears to be a slider under the coaxial knobs which I assume is a POL slider?

Yes.

One last comment here would be that the DIC system with the separate prism slider and polarizer slider, is mechanically much simpler than the standard combined system. It may therefore be less prone to failure than the standard combined slider, though that is completely a surmise on my part.

Leonard

[René]

[Given the NA .52 limit of the Nikon DIC LWD condenser, and given the likely need/desire to use LWD objectives, high magnification objectives are of limited usefulness on the standard Diaphot.

Don't dismiss high mag objectives for this reason. I've worked routinely on an Olympus IMT2 with 0.55 condenser and 60x/1.4 oil lens in BF. I agree DIC doesn't add much information with the 60x lens at this limited condenser aperture, but it is very nice for imaging.

You can easily make small microaquaria by taping large coverlips on slides with a spacer, glue large coverslips on tubing, there are nowadays even single use chambers for inverted microscopy. The gain in image quality of normal versus LWD objectives is immense, so get rid of them!


Good luck! The Diaphot is one of the great scopes of 'our' times

René

ps, It is also very easily adaptable to LED fluorescence, if you ever feel a need for that.

[ldflan]

Hi, René -

Well, higher magnifications are OK on the .55 NA DIC condenser for the Diaphot, but the results are inevitably limited and there isn't much point in using the scope as configured for that, to my way of thinking. If nothing else, using high NA objectives on the Diaphot requires super thick immersion oil, and it's a pain to clean given the configuration of the scope.

Like I mentioned, though, you can modify the Diaphot to function with high NA condensers from the later 200/300 series, and using those condensers you can get the full (or nearly full) capabilities of high magnification objectives when you flip your slide over (or otherwise image through a coverglass instead of the slide.)

In particular, there is an uncommon Nikon 60x LWD objective of higher NA (.85 I think) that work really well with the .85 high and dry condenser and DIC prism for the 200/300 series when cobbled onto the Diaphot. The .85 NA condenser actually leaves enough room between the condenser lens and the slide to use micromanipulator needles in a drop of fluid.

For ordinary high power objectives, a box of culture well slides with coverglass bottoms are nice to have for use with the Diaphot. They also don't leak unless you break them, unlike arrangements sealed with VALAP, tape, etc. The chambers are a bit expensive and fragile, but worth having.

I hear you on the image quality difference between LWD and normal working distance objectives. But the Nikon LWD objectives are critical to using the Diaphot in its intended role - imaging through culture vessel bottom, through petri dishes, through temporary slides, etc. Getting rid of the LWD objectives is not in the cards for that reason alone. I have also generally found that they perform very well in their intended role, and give good DIC images that are usually fully adequate for many micromanipulation tasks.

Yes, the Diaphot is definitely a great scope. The fact that they made so darn many of them for so long proves it. It's undoubtedly the most broadly useful and capable light microscope that I have had the pleasure of using. In terms of a piece of industrial art, theoretical versatility in configuration, and the sheer joy of manipulating gorgeously machined parts, I doubt anything can beat a Reichert Zetopan. At least that's my opinion.

But for a classic rig that gives great results across a broad spectrum of biology applications and imaging techniques, the Diaphot is very hard to best, and it offers considerably more capability per dollar invested than any other scope I know.

In terms of LED fluorescence light sources, I really don't think we are there yet - at least not at any reasonable price point. I haven't looked into it in a few years. If you can point me to an LED UV source that has been shown to have a broad enough spectrum to be useful with even a small range of standard fluorochromes (TRITC, FITC, DAPI equivalents at a minimum), I would love to know about it!

I've done some DIY work on this, and concluded there is really no way around having to swap out LED sources to optimize the output spectrum for your particular fluorochrome, and even then getting a diode with enough power is a challenge. For now, I am not convinced that there is any realistic LED alternative to mercury/xenon bulbs for the usual range of fluorochromes, much less a system that will actually do a professional job while remaining within financial reach of most individuals... It would sure be nice if someone could figure it out.

I do have an LED source for transmitted light instead of the halogen lamphouse - I use a 20 watt version built by Stan at Retrodiode. It's very good, though like most LEDs it has a little too much purple to the light, and could use a wratten straw filter or GIF to help with the chromatic aberrations that tends to create. Retrodiode offers at least two power supplies for their systems. The more expensive one has a refresh rate that does not interfere with my Sony digital camera display, so I would consider that one over the basic model, which has a power signal that creates lines on the camera preview screen.

Leonard

[Lou Jost]

I've just now built a primitive fluorescence illuminator out of an optophot epi illuminator and a UV flashlight. It works! Not very strong, since there is no dichroic mirror, but I am having great fun seeing this new world.

[Lou Jost]

The epi-illuminator works on its own, without a microscope, used between an infinity objective and the tube lens. I can freely move it between the finite Optiphot and the infinity rig.

[ldflan]

I hope you put a UV barrier filter somewhere in the tube before the eyepieces!

Leonard