Can one adjust a condenser dovetail?

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farnsy
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Can one adjust a condenser dovetail?

#1 Post by farnsy » Mon Jul 12, 2021 12:10 am

My microscope does not have a aplanatic/achromatic condenser available for it. I have a Nikon NA 1.4 aplanat/achromat condenser that I would like to use. The dovetails are almost the same, but not quite. The Nikon fits almost all the way into my condenser carrier, but near the back there is a lip that prevents it from going all the way in. It is maybe 1-2 mm too large.

You can see a comparison of the dovetails here. The top one is the nikon, the bottom is an abbe condenser that fits in my microscope.

Image

The nikon doesn't seem to have any very visible screws so I have no idea how one would remove the dovetail, if such a thing is even possible.

Here's the condenser carrier.
Image

I'm trying to figure out if there's a way to make this work. I have no experience with metalwork. Do you think this is something a metalworker could adjust easily and without breaking anything (mill down the Nikon dovetail)? I mean, I guess I could also use a file and do just one side. It would be nice if it would still end up centered correctly, though my carrier can center.

Alternatively, the lighter metal in my condenser carrier seems to be something that can be removed. Maybe I could 3D print something that fits in the same area and accepts both dovetails. A spring-loaded solution, maybe.

Any thoughts on this? I guess I could also just give up on the idea, but I was quite hopeful about using this condenser with my higher NA objectives.

apochronaut
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Re: Can one adjust a condenser dovetail?

#2 Post by apochronaut » Mon Jul 12, 2021 12:50 am

Sometimes dovetails can be removed but your pictures don't show enough detail.
I see that you are using a .90 condenser. Did you not get an oil condenser with the DIC or is that still in transit?

farnsy
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Re: Can one adjust a condenser dovetail?

#3 Post by farnsy » Mon Jul 12, 2021 12:56 am

apochronaut wrote:
Mon Jul 12, 2021 12:50 am
I see that you are using a .90 condenser. Did you not get an oil condenser with the DIC or is that still in transit?
I don't use this abbe condenser. Just using it as a reference. I normally use my DIC or Phase contrast condensers, both if which can be oiled. I have a flip top I can use as well. This one I bought just because I didn't know if I might need it and they weren't very good at explaining why it exists and the incremental cost as low. Turns out I don't need it. Would be happy to cannibalize it for parts if that becomes an option.

My abbe condenser has a top that screws off and the dovetail and diaphragm can be removed by removing a few screws. The Nikon does not seem to screw apart and I can see no screws at all. I have no idea how it can be taken apart.

If you take a look in the "beginners" forum you will see a thread about my DIC condenser. It's exactly the same as my phase condenser. Just has prisms in place of annuli.

PeteM
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Re: Can one adjust a condenser dovetail?

#4 Post by PeteM » Mon Jul 12, 2021 2:01 am

Assuming the dovetail is just a bit too large, it can be turned down in a lathe.

It can be chucked either internally or externally, and a narrow profile turning tool used to replicate the dovetail angle (just a bit smaller). Kind of a shame to modify such a nice Nikon condenser through. FWIW an unmodified Nikon will also fit Olympus. Yours seems more like the still smaller dovetail of AccuScope etc.

farnsy
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Re: Can one adjust a condenser dovetail?

#5 Post by farnsy » Mon Jul 12, 2021 2:45 am

Yeah, it is a nice condenser, and could be sold if for some reason it doesn't work out for me and I don't modify it. Maybe I should be focused on replacing the carrier with something I design and 3D print. The problem is, I'm not that great at 3D designing. I can put plenty of time into this, though, and do a few iterations.

I don't really know what standard my condenser carrier conforms to. My scope is identical in most or all respects to an AccuScope EXC-500 and the optics are compatible with Nikon's. The body looks very much like a Nikon Ci, but I guess the condenser carrier is a more generic Chinese one. If AccuScope uses the same condensers for its EXC-500 and its Infinity/180/45/RMS microscopes, that would be nice. Certainly all of my condensers look very generic. Is there any standardization in the condenser dovetails sold by Chinese manufacturers?

Actually I fail to see why Chinese manufacturers would choose a different standard than that of one of the big manufacturers. Most of their infinity optics are compatible with Olympus, so why not make the condenser mount the same? Unfortunately not everyone in the world sees things my way.

PeteM
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Re: Can one adjust a condenser dovetail?

#6 Post by PeteM » Mon Jul 12, 2021 6:23 am

If you have a 3D printer and enough room under the stage (which is likely), you could 3D print an adapter/carrier for the Nikon 1.4na condenser. Top part is female with some setscrews coming in from the side to capture the Nikon dovetail. Bottom replicates your scope's smaller dovetail. Pretty simple modeling task - the condenser needs about an extra cm. or so room under the stage. I'd just drill and tap the setscrew holes rather than attempt to print them.

farnsy
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Re: Can one adjust a condenser dovetail?

#7 Post by farnsy » Mon Jul 12, 2021 7:09 am

Yowza, Pete, that's a really good idea. Funny how it didn't occur to me to print an extension to the Nikon condenser dovetail instead of trying to change my current carrier.

Actually I can do one easier as a test case. I removed the dovetail from my abbe (remember, I don't use it) and what do you know? It has a little lip that fits nicely inside the dovetail of the Nikon and holds it in place. About a mm of play, which means I can center it by hand without using any set screws.

Image

Here it is on the scope

Image

It works great. The edges of the field diaphragm are crisp white and black with no color fringing at all. That's my first time seeing that through a microscope. Very nice!

Too bad I can't rig this to my DIC condenser. I hate changing condensers out. Unfortunately, if I did rig them together, the prism would no longer be super close to the condenser diaphragm, which I believe is necessary, right? Probably not enough space under the stage to do that, either.

Anyway, I really appreciate your idea, man.

apochronaut
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Re: Can one adjust a condenser dovetail?

#8 Post by apochronaut » Mon Jul 12, 2021 1:15 pm

Are you using the 1.4 condenser oiled?

farnsy
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Re: Can one adjust a condenser dovetail?

#9 Post by farnsy » Mon Jul 12, 2021 6:18 pm

Not yet, but I will, more frequently I'll use a drop of water on there.

I think I need to make a 3D printed part that holds this rigidly to replace this dovetail kludge. Having lateral play is a bit of a pain as the condenser often moves when I am adjusting it's diaphragm. I can use it right now, but the project is not done.

apochronaut
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Re: Can one adjust a condenser dovetail?

#10 Post by apochronaut » Mon Jul 12, 2021 8:08 pm

farnsy wrote:
Mon Jul 12, 2021 6:18 pm
Not yet, but I will, more frequently I'll use a drop of water on there.

I think I need to make a 3D printed part that holds this rigidly to replace this dovetail kludge. Having lateral play is a bit of a pain as the condenser often moves when I am adjusting it's diaphragm. I can use it right now, but the project is not done.
It will also move due to drag from the immersion medium.

Without oil , your condenser functions somewhere between .90 and .95 N.A., certainly enough to keep the objectives you are using happy. However, in trialling various 1.4 N.A. condensers both oiled and dry, their performance seems to suffer more from not being oiled than an abbe aspheric 1.25. The oil space between the slide and the condenser is integral to it's achromatism ; it needs an n homogeneity of the successive layers in the medium stack between the condenser and object . Leaving air in between the condenser and the bottom of the slide not only reduces the N.A. but it also introduces some ca into the illumination beam, somewhat negating the benefit of having an achromat condenser. Dedicated .90 dry condensers factor in the air space and in the case of a .90 achromat, will outperform other condensers built to a homogeneous tolerance, whether achromat or not and whether they are high N.A. or not.

Certainly, if you eventually spring for the 1.30 plan fluor or the 1.45 planapo, having a 1.4 achromat will be highly beneficial but only if you oil it.
To illustrate the negative effects of not oiling a high N.A. oil condenser one can use the Rayleigh Criteria to calculate the theoretical resolution of your 1.10 water immersion objective with mid wavelength green light. I am assuming that unoiled condensers work at .90 N.A. but some might work a little higher.
1.22 X 500 ÷ (.90 + 1.10) = .305 microns . Oil the condenser and it is . 1.22 X 500 ÷( 1.10 + 1.10 ) = .277 microns. .

In comparison the difference with the 1.30 plan fluor objective and an unoiled condenser is thus.
1.22 X 500 ÷ (.90+1.30) = 2.77 microns, or the same as the water immersion using an oiled condenser however, the 1.30 plan fluor suffers much less from the detail masking due to the refraction typical of achromats. Oiled , the 1.30 yields 1.22 X 500 ÷ ( 1.30 + 1.30) = .235 microns.

The importance of oiling the condenser is further illustrated by the fact that a typical and standard system such as a 1.25 abbe condenser used with a 1.25 oil immersion abbe condenser will achieve 1.22 X 500 ÷ (1.25 +1.25) = .244 microns theoretically , whereas the same condenser unoiled or a .90 achromat used with a 1.4 N.A. objective will achieve only 1.22 X 500 ÷ ( .90 + 1.40) = .265 microns. theoretically. Less than a ubiquitous 1.25 achromat. It doesn't make any sense to splurge for an expensive plan fluor or planapo objective and not use an oil immersion condenser.
Replacing oil with water probably does not make sense either. In tests that I did with 5 different condensers to fit the AO/Reichert Diastar, I trialled them all dry, with water and with Cargille type A immersion oil. The 5 condensers were # 1202 .90 achromat aplanat dry, # 1970 1.25 abbe aspheric oil immersion, # 1973 1.40 achromat aplanat oil immersion, a self built achromat based on a #1973 blank including the 1.4 top lens( no immersion requirement determined, although the top lens requires oil in order to obtsin 1.4 N.A.) and a self built apochromat based on a # 1973 blank including the 1.4 top lens ( same immersion status as the former).
The results were in order of preferance in actual use with an N.A. 1.30 plan fluor objective.
Dry ; 1) self built achromat, 2) .90 achromat aplanat 3) 1.25 abbe aspheric, 4) 1.4 achromat aplanat 5) self built apochromat. The preferance here is based on the higher luminance of the self built condenser and the fact that it appears to be a slightly higher N.A., perhaps as high as .95.

Water: 1)self built apochromat. 2) self built achromat. 3) 1.25 abbe aspheric. 4) 1.4 achromat aplanat. 5) .90 achromat aplanat. The preferance here was based on luminance, colour correction and the ability to achieve Köhler. None of the condensers with water were better than several others dry or most oiled. Some had odd colour artifacts.

Oil : 1) 1.4 achromat aplanat. 2) 1.25 abbe aspheric 3) self built apochromat. 4) self built achromat. 5) .90 achromat aplanat.

Order of overall preferance. 1) # 1973 1.4 N.A. achromat aplanat oiled 2) self built achromat , dry 3) # 1970 1.25 abbe aspheric oiled 4) # 1202 .90 achromat aplanat dry 5) # 1970 1.25 abbe aspheric dry.

Just because a condenser is an immersion condenser, that doesn't mean that another immersion medium will work better than air.
Last edited by apochronaut on Tue Jul 13, 2021 6:43 pm, edited 1 time in total.

farnsy
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Re: Can one adjust a condenser dovetail?

#11 Post by farnsy » Mon Jul 12, 2021 8:18 pm

[double post]
Last edited by farnsy on Mon Jul 12, 2021 8:25 pm, edited 1 time in total.

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Re: Can one adjust a condenser dovetail?

#12 Post by farnsy » Mon Jul 12, 2021 8:18 pm

That's interesting. I thought I had read somewhere that the effective difference between using water and oil on a condenser wasn't really that significant. But I bet that was tested using a 1.25 abbe. Well, I'm open to using oil down there too. Will have to do some testing once I get this put together. I'm printing a first pass at a dovetail adapter right now. By the end of the day I expect to have the bugs worked out and I can start trialing this. Though, my highest NA objective at the moment is an achromat 1.1 WI, so the effective difference between these condensers may not be significant.

I wasn't 100% clear on your ranking of dry vs water. To be clear, did you find that your 1.25 achromat condensers worked better dry than wet (with water)? That would definitely be a surprise to me, but I am open to being surprised.

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Re: Can one adjust a condenser dovetail?

#13 Post by apochronaut » Mon Jul 12, 2021 10:23 pm

None of the condensers immersed in water were that good but my objective was a 1.3 N.A. plan fluor , so it demanded a well corrected light source with sufficient N.A.
Water's n is just over 1/2 way between air and immersion oil , so it probably reduces the N.A. of the condenser considerably, plus defocuses it and creates some ca. To present a reverse scenario, if you immersed a .90 dry condenser in water would it improve such a condenser? No, it doesn't.
I would guess that immersing a 1.4 achromat oil immersion condenser in water would lower it's N.A. to about 1.2 or so. Since you are using a 1.1 N.A. objective, the condenser can actually only work at 1.1 N.A., the same as it would have if oil immersed but the difference is that when oil immersed it is an achromat, when water immersed or used dry, it is no longer an achromat. It's achromatism is determined by it passing the light to the object through an homogeneous medium.

A dry achromat .90 condenser with your 1.1 N.A. objective has a theoretical resolution of .305 microns with 500 nanometer light, as calculated in the earlier post. Since your objective has an N.A. of 1.1, that limits the effective N.A. of any condenser used with it to 1.1. It's theoretical resolution limit under standard substage illumination and that same monochrome light source is .277 microns. Is a 1.4 N.A. condenser using a non optimized immersion medium going to yield a better image than a 1.25 oil immersed abbe condenser using optimized immersion or even a 1.25 abbe condenser water immersed? I think the deleterious ca caused by the use of water would have less effect on the abbe than on the achromat.
Considering the alterations of a condenser's corrections is as important as the N.A. Despite the fact that a .90 achromat condenser limits a 1.1 N.A. objective to a theoretical resolution .028 microns geater than a condenser working at 1.1 N.A. , the fact that it is a well corrected condenser will have definite bearing on the image.
Last edited by apochronaut on Tue Jul 13, 2021 6:48 pm, edited 3 times in total.

farnsy
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Re: Can one adjust a condenser dovetail?

#14 Post by farnsy » Mon Jul 12, 2021 11:11 pm

Dang. I guess it makes sense that condensers would need to be used with the medium for which they were optimized. They are, after all, basically objectives below the stage. We wouldn't expect an oil immersion objective to work properly with a water or air medium. I'm not 100% against oil on the condenser of course...I will give it a shot and see how I feel about it. I find it less troublesome on the condenser and bottom of the slide than on the top of the slide cover. I do have a 100X oil objective (achromat), but I have been enjoying my 100X water so much I'm unlikely to change it out. My 100X phase is also oil, of course, so there's no getting away from oil completely.

So I guess 1.4 NA aplanat/achromat condensers are only achromat/aplanat when used with oil? The color fringing on the field diaphragm blades is super minimal (non existent) when using it dry, which is why I was thinking it was working well--there is quite a difference between this Nikon condenser and my abbe (both 0.9 and 1.25) examples in that respect. Maybe the engineers designed it so it would work pretty well dry as well as oiled, knowing that many people would use it that way?

farnsy
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Re: Can one adjust a condenser dovetail?

#15 Post by farnsy » Mon Jul 12, 2021 11:18 pm

Here is my V1 condenser adapter. This one is not centerable...I just holds the dovetail with friction, but it's pretty well centered. The condenser mount, of course, can be centered, but I don't want to change it from the position that works with my other condensers. I don't currently have tools to tap threads and make this adapter centerable, but I'll get some and adjust my model to have thicker walls and a little play.

Here's the adapter, hot off the printer

Image

And mounted on the condenser

Image

I gave it a little trial run in the microscope and it works pretty well; I'm able to insert it all in one piece. 3D printers are fun!

By the way, Pete, does it not work to just drill a hole a little narrower than the screw and let the screw do its own tapping in the plastic?

apochronaut
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Re: Can one adjust a condenser dovetail?

#16 Post by apochronaut » Tue Jul 13, 2021 2:03 am

No condenser can be over an N.A. of 1.0 without an immersion medium. Nikon are good optical designers not wizards.

farnsy
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Re: Can one adjust a condenser dovetail?

#17 Post by farnsy » Tue Jul 13, 2021 2:41 am

apochronaut wrote:
Tue Jul 13, 2021 2:03 am
No condenser can be over an N.A. of 1.0 without an immersion medium. Nikon are good optical designers not wizards.
Haha. What I meant was that they may have attempted to design it so that chromatic and spherical aberrations are reasonably low at both 0.9 NA dry or 1.4 NA oiled. I do not know how feasible that would be, though. The fact that you observed strange color fringing when using water with an aplana/achromat condenser suggests that it may not be.

apochronaut
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Re: Can one adjust a condenser dovetail?

#18 Post by apochronaut » Tue Jul 13, 2021 2:26 pm

The d.i.y. apochromat that I made up has the least colour fringing of all the condensers tested above. It has the poorest performance of them all, and only the best with water because the others are not that good. I'm not sure where the degree of dispersion occurring at the field diaphragm fits in. There is no doubt that more highly corrected condensers seem to produce cleaner field diaphragm edges but that doesn't necessarily translate into better performance.

Perhaps I need to do a more thorough assessment of immersion mediums . Discussions tend to revolve around dry, water or oil but one of the resistance points of using oil with some users is the cost and access to immersion oil. Immersion oil is intolerably expensive now. It has an n of just under 1.52. One could substitute corn, soybean or linseed oil : all with a refractive index of around 1.47, so there would be only a very slight loss of resolution with the highest N.A. objectives.

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