Metallurgy objectives

[Rossf]

I guess this should be a newbie question but how are metallurgy objectives different optically from transmitted light objectives? Or are they not? Also why are they often 215mm or similar than 160mm? ( apart front the epi attachments lengthening the optical path). I want to video soil samples to capture micro critters in situ as well as usual transmitted light upright slide/Petri inverted work-I did some experiments with standard objectives and was able to see nematodes,tardigrades and Martian looking mites in incident light (LWD objectives letting in enough light) but they weren’t that clear, not because of their semi-translucency but just kinda a bit blurry-Maybe cos they are corrected for coverslips? would metallurgy objectives do this job better because they are designed for non transparent samples and no coverslip?
Regards ross

[Scarodactyl]

Yeah, the main difference is that they are corrected for no cover slip. They are also often designed for longer working distances (and thus lower resolutions).
The longer tube le gth is just to account for the illuminator without having to compensate with added lenses (some chose to do that, which tends to also add extra mag) or without having to redesign the stand from scratch vs transmitted setups (others did that).

[Rossf]

Thanks Scarodactyl. Now on the hunt for LWD metallurgy objectives...not Nikon though-they seem so expensive on fleabay no matter the era.

[Scarodactyl]

Nikons are in high demand because they can be hooked up directly to a camera without missing any vital eyepiece corrections, and elwd objectives are especially handy for external oblique illumination. But plenty of other makers made them too. What kind of system are you using? Or are you looking for a complete metallurgical style scope?

[Rossf]

I don’t need a metallurgy scope system but just wanted to experiment with using LWD non cover slip corrected objectives to show microbes (large semi opaque ones like I mentioned) on the surface of compost,moss,soil etc-ie a sample in a small dish using upright scope and incidental light-maybe with LED light ring-so won’t be using directly on camera like some do with the Nikon’s -also I live in finite land with microscopes-I’ve observed before nematodes going in and out leaving tunnels just like normal sized worms-just want to emphasise the aeration they and other small critters create in the soil in situ-rather than just ‘classic’ transmitted light footage. But obviously not with coverslip objectives...thanks for the advice. I guess the other way is to invest in a stereo scope which I’ve been thinking of for a while, for other tasks as well.
Regards ross

[Scarodactyl]

Everyone should own at least one stereo, preferably a half dozen.
What brand are you using? Just to think if I've seen any good deals on compatible or close-enough epi objectives.

[Rossf]

Mainly Olympus ch-1,ch-2 but I’m in no way monogamous when it comes to objectives-I mix match zeiss,leitz,Nikon-that’s why I stay in finite land-I don’t aspire to super high N/A and haven’t noticed any real problems using Olympus c-mount reducer and NK or NFK eyepieces with all mentioned brands.but I do video only-not into stills.any slight aberrations are probably less noticeable on moving images vs stills-I call it “action distraction’!
Regards ross

[BramHuntingNematodes]

As an addendum I could point out the metallurgical objectives for reflected dark field have additional differences which don't necessarily prevent them from being used in transmitted light settings but diminishes the working distance and sometimes requires a different thread standard. You should be able to tell these apart because they are fat to accommodate some additional machinery inside.

[Rossf]

BramHuntingNematodes I thought of you the other day-I make high thermal compost-soon as it gets to 60-70 degrees Celsius I remake so I don’t bake.At first it’s insane levels of very motile aerobic bacteria-after a few turns (about a week maybe two) you let it settle when stable around 25-30 degrees-then the protist and nematodes proliferate-I saw a small spot of goo that was quivering and shimmering-when I put some under the scope the nematodes were simply uncountable-at 4x objective! Large ones too.I went all the way up to my treasured 100x water immersion and the sheer squirmy chaos was hilarious-I’ll take some footage and post it in the next day or two hopefully for your amusement-you could probably identify different ones-I notice some have quite a squarish mouthpiece,others more round. Have you ever seen that canabalistic one with the spear like structure in its mouth? Only seen in photos.
Regards ross

[BramHuntingNematodes]

Hooray bring on the 'todes. Nematode taxonomy is undergoing enormous shifts. Any keys I might use may therefore be outdated. A pronounced and vicious looking stylet is a feature on many nematodes, but I'll do my best!