Buying an 20X objective with long working distance

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david.rojillo
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Buying an 20X objective with long working distance

#1 Post by david.rojillo » Mon Jul 26, 2021 9:26 pm

Hello all,

Recently I upgraded to an infinity corrected microscope, but as usual it has the common 4X,10X,40X and 100X set up. I wanna buy an 20X objective that is the most useful for me, as my hobby is to look into water samples.

I have start searching for a 20X plan infinity objective, and most of the working distances I found are from 0,65mm to 1mm. That is not good enouhg for me, becasue many times I want a thick water layer or even use slides with cavities where specimens can move freely.

I have seen that mettalugical objectives have specifications of 20X Plan infinity corrected and huge working distances and 0,5 NA as 8mm (20X /0.5NA, oo/-)

Can metalurgical objectives be used in a regular biological microscoper with trasnmited light? What if I put a coverslip? Is it a must to use them without coverslip?

(I see that 4x and 10X objectives can be used with and without coverslip..., is the same for metalurgical objectives?) Will they work as biological objectives but with longer working distance?

(In my steromicroscope I use both iluminations with same obejectives, but it seems that reflected light gives the best image... will that be the same for metallurgial objectives?)

Sorry if those questions are very stupid, but I do not know if that will work.... :oops: :?:

If not working for trasnmitted light I will have to look for a 20X with at least 1,5 mm working distance...

BramHuntingNematodes
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Re: Buying an 20X objective with long working distance

#2 Post by BramHuntingNematodes » Mon Jul 26, 2021 11:33 pm

There's a Nikon CFL objective inf. TL and coverslip corrected with a near 4mm wd. Look around maybe
1942 Bausch and Lomb Series T Dynoptic, Custom Illumination

apochronaut
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Re: Buying an 20X objective with long working distance

#3 Post by apochronaut » Mon Jul 26, 2021 11:51 pm

Switching infinity corrected objectives around can produce pretty lousy imaging. Even if your microscope is a Chinese infinity scope, it was built to conform to the specs. of one if the longer established companies. Most are based on the 45mm parfocal Nikon 200mm reference length or Olympus 180mm reference length systems and it is wise to use an objective that was engineered to the needed specifications. A few are Meiji and I have come across one or 2 that are 45mm parfocal versions of the old AO system.
Perhaps if you post a picture of your objectives, they might be able to be narrowed down.
You didn't identify a brand or system.

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patta
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Re: Buying an 20X objective with long working distance

#4 Post by patta » Tue Jul 27, 2021 7:37 am

A list helping to spend a lot of money in long working distance 20x s
https://www.photomacrography.net/foru ... =43827

david.rojillo
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Re: Buying an 20X objective with long working distance

#5 Post by david.rojillo » Tue Jul 27, 2021 8:10 am

You didn't identify a brand or system.
Sorry for that, my fault. My system is a ZUZY 122/148 model, but that is just a spanish brand for Chinese imported microscopes. They are similar to AMSCOPE microscopes (Pretty sure same manufacturer). Those objective are (UIS - Universal infinity System) Olympus 180mm... but I understood from other post that infinty objectives can be interchanged without much loss of quality (maybe a slgihtly different magnification).

So, using metalurgical objectives, even they are plan and infinity corrected, would not work properly?

There's a Nikon CFL objective inf. TL and coverslip corrected with a near 4mm wd. Look around maybe
That I will check... probably ebay or other second hand markets... 4mm is more than enough... :)

Many thanks for your replaies...

Scarodactyl
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Re: Buying an 20X objective with long working distance

#6 Post by Scarodactyl » Tue Jul 27, 2021 4:00 pm

Not all infinity objectives are interchangeable, it's just that a slight difference in tube length isn't a dealbreaker. Corrections and parfocal length can be though--Nikon cfi60 infinity objectives are optically compatible with Olynpus heads but the extra 15mm of parfocal length makes them impractical to use on an Olympus body, at least if you don't want to constantly be putting it on and taking it off and racking the stage up and down. On the other hand nikon CF Plan infinity objectives are rms and 45mm parfocal and fit fine on an Olympus microscope, though they only made metallurgical objectives in that particular line.
But if you tried a Zeiss infinity objective you'd probably get really terrible visual quality because their lenses require specific corrections in the tube lens. There are similar issues of varying degrees for many other makers, so it isn't quite a free-for-all on mixing and matching.

If you get a metallurgical objective its performance will be lower with a cover slip, at least if the NA os above 0.30. Nevertheless it may still be acceptable a little above that.

Dubious
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Re: Buying an 20X objective with long working distance

#7 Post by Dubious » Tue Jul 27, 2021 7:04 pm

Mainly, be sure you can return the objective if it doesn't work out. Even if you find one that is reasonably compatible with your microscope, you may find that chasing focus in a thicker layer of water is simply too frustrating.

apochronaut
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Re: Buying an 20X objective with long working distance

#8 Post by apochronaut » Tue Jul 27, 2021 7:54 pm

Nikon also has a 45mm parfocal infinity cover slip corrected system as well, which the Chinese NIS45 system is patterned after. The NIS45 objectives are quite compatible with Reichert infinity corrected 45mm parfocal objectives, just yielding a slightly lower magnification of about 92% but otherwise yielding excellent balanced ca and other aberrations across the field. This is with slightly compensating eyepieces tuned to the Reichert objectives.
Olympus infinity objectives yield about the same magnification in the Reichert system due to a close similarity in the reference lengths but there is some difference in lateral ca. Overall Olympus objectives give poorer imaging in the Reichert system than NIS45.
What this points to is that the shorter tube of the Reichert system applies overcorrection to the NIS45 objectives, enough that they work similarly to the Reichert objectives when both are used with eyepieces exhibiting the same degree of compensation.
While Olympus objectives also start out with more or less the same magnification in the Reichert system, the image is overcompensated through the Reichert downstream optics, yielding some small amounts of lateral ca that the NIS45 objectives do not display.

I would be concerned that Olympus pattern and NIS45 objectives would run into a subtle mis-match beyond that of magnification.

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Re: Buying an 20X objective with long working distance

#9 Post by Scarodactyl » Tue Jul 27, 2021 8:02 pm

Oh that's interesting, I've never run into coverslip-corrected 45mm infinity Nikon objectives. Can you link me an example? That might be something to keep an eye out for.

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Re: Buying an 20X objective with long working distance

#10 Post by apochronaut » Tue Jul 27, 2021 10:24 pm

Their lower end objectives are all made in China. Even the lower end NIS60 objectives. They just call them CFI60. Just look for anything NIS45. R.M.S. threads , 45mm parfocal . NIS stands for Nikon Infinity System. Granted there aren't a broad range of options as it is with the Eclipse100 R.M.S. series objectives but the Chinese have extended the NIS45 beyond what Nikon has used or wanted to.
There is a nice planachro water immersion 100X 1.10 N.A. , planachros : the BE plan line obviously and some planfluors but with some of those you have to preorder and they will make them. They show up as an option you can order for certain models of scopes.
Nikon wouldn't have done much on the level of making advanced R.M.S. infinity objectives would they have? They wouldn't have wanted to let the Eclipse100 or now the new Ei to be able to be extended too far because then those educational scopes might cut into the potential sales of the Eclipse200. Even with the Eclipse 200, they want to upsell to the E400 in order to get the perks like DIC.

I use the R.M.S. NIS45 100X 1.10 water objective quite frequently now. It is very good in a Reichert series 400, with very slightly compensating oculars as described ahove. Neutral oculars give a little more ca. Probably, the best would be something in between. I haven't tried any B&L but I should. I think the Balplan eyepieces are just a tad compensating.
The Olympus version of that objective requires correcting oculars in a 400 stand . Neutral gives ca and compensating worse yet. PZO 10X SK are perfect but they only get to 18mm. They are the best I have found yet.

Scarodactyl
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Re: Buying an 20X objective with long working distance

#11 Post by Scarodactyl » Wed Jul 28, 2021 5:05 am

Ahhhh of course the e100 objectives. I totally forgot those.

david.rojillo
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Re: Buying an 20X objective with long working distance

#12 Post by david.rojillo » Wed Jul 28, 2021 6:09 am

If you get a metallurgical objective its performance will be lower with a cover slip, at least if the NA os above 0.30. Nevertheless it may still be acceptable a little above that.
Then they will not work, as most of the 20X mettallugical objectives I have seen they have a NA above 0.5.

After all your comments I think I will look for compatible objective with Olymous UIS system to avoid running into troubles.

Nevertheless I will serach for at least 2.0 mm working distance, that I think it is the minimum acceptable for a 20x objective. (When looking into 'fresh water' I do not want to be all the time pending not to touch the coverslip... when following the specimens that move around, with long bodies, from bottom to top...).

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Re: Buying an 20X objective with long working distance

#13 Post by Scarodactyl » Wed Jul 28, 2021 6:28 am

I'd throw a bid at this one.
https://www.ebay.com/itm/Infinity-Corre ... 4852936194
Might go cheap, and with an NA down at 0.40 there's a chance it will have enough wd. You also wouldn't have to worry about using it even if you're waiting for a deal on a longer wd objective to come up.

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Re: Buying an 20X objective with long working distance

#14 Post by hans » Wed Jul 28, 2021 6:37 am

david.rojillo wrote:
Wed Jul 28, 2021 6:09 am
If you get a metallurgical objective its performance will be lower with a cover slip, at least if the NA os above 0.30. Nevertheless it may still be acceptable a little above that.
Then they will not work, as most of the 20X mettallugical objectives I have seen they have a NA above 0.5.
...
(When looking into 'fresh water' I do not want to be all the time pending not to touch the coverslip... when following the specimens that move around, with long bodies, from bottom to top...).
You get the same problem trying to look deep into water, are you sure working distance will be the limiting factor? The effect scales quickly with NA but for example at 40X/0.66 0.55 mm WD the image looking into water under 0.17 cover glass gets really bad (spherical aberration) well before the objective hits the cover glass.

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Re: Buying an 20X objective with long working distance

#15 Post by viktor j nilsson » Wed Jul 28, 2021 7:14 am

apochronaut wrote: Even with the Eclipse 200, they want to upsell to the E400 in order to get the perks like DIC.
Minor point: you actually need to go up to the E600 to be compatible with DIC. The frame of the E400 needs to be cut to fit the DIC nosepiece:

https://www.photomacrography.net/forum/ ... hp?p=82446

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Re: Buying an 20X objective with long working distance

#16 Post by apochronaut » Wed Jul 28, 2021 11:27 am

https://www.microscopyu.com/museum/eclipse-e400
I never owned one or used one . I flirted with buying the Chinese clone of the E200 that does have DIC about 6 months ago and when I went to the literature on the Nikon E200 was surprised to see that Nikon did not have DIC for it. The lierature did point to the fact that the E400 did though. A full brochure shows a photograph of the entire DIC system layed out.
It seems that the E400 has an off the shelf system but the PMF poster was trying to retrofit parts from another system. Perhaps Nikon uses a slightly modified version of one of the systems used on the Chinese E200 body for the E400. There is also an Indian E200 type system that uses Seiwa optics. They advertise that their optics and phase systems are Japanese, made by Seiwa. Would seem likely that the DIC would be too.

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Re: Buying an 20X objective with long working distance

#17 Post by viktor j nilsson » Wed Jul 28, 2021 11:42 am

apochronaut wrote:
Wed Jul 28, 2021 11:27 am
https://www.microscopyu.com/museum/eclipse-e400
I never owned one or used one . I flirted with buying the Chinese clone of the E200 that does have DIC about 6 months ago and when I went to the literature on the Nikon E200 was surprised to see that Nikon did not have DIC for it. The lierature did point to the fact that the E400 did though. A full brochure shows a photograph of the entire DIC system layed out.
It seems that the E400 has an off the shelf system but the PMF poster was trying to retrofit parts from another system. Perhaps Nikon uses a slightly modified version of one of the systems used on the Chinese E200 body for the E400. There is also an Indian E200 type system that uses Seiwa optics. They advertise that their optics and phase systems are Japanese, made by Seiwa. Would seem likely that the DIC would be too.
Aha! Yes, in that case, it seems like the E400 uses a slightly different system. Thanks for digging that up!

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Re: Buying an 20X objective with long working distance

#18 Post by david.rojillo » Thu Jul 29, 2021 10:51 am

I'd throw a bid at this one.
https://www.ebay.com/itm/Infinity-Corre ... 4852936194
Might go cheap, and with an NA down at 0.40 there's a chance it will have enough wd. You also wouldn't have to worry about using it even if you're waiting for a deal on a longer wd objective to come up.
It is good bargain... but it is a pitty it does not ship to Spain. :( :( But I will keep searching in ebay for objectives in Europe...


I
You get the same problem trying to look deep into water, are you sure working distance will be the limiting factor? The effect scales quickly with NA but for example at 40X/0.66 0.55 mm WD the image looking into water under 0.17 cover glass gets really bad (spherical aberration) well before the objective hits the cover glass.
I think you are right, specially for 40x, but 20X with 0,4, normally allows me to move almost 1 mm up and down from the coverglass to the botom of slide with cavity, although I have to recognize that 10X is best for doing that. (Sometimes even without coverglass images are good enough, but moving slides causes earthquake in the fauna :) )

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Re: Buying an 20X objective with long working distance

#19 Post by apochronaut » Thu Jul 29, 2021 1:45 pm

Have you considered using a 10X objective and WF 15 or 20X eyepieces? You would have the working distance but lose a little eye relief. There are some really good 15X with outstanding f's.o.v. and pretty good eye relief. 20X might be a little harder to work with but possible.
I wouldn't worry too much in that application whether or not the objective was plan or not. There isn't going to be that much advantage unless the non plan objective had severe coma or lateral ca, which is unlikely.

An option to try if you go the route of a met. objective is to use a very thin coverslip. They are available as thin as .08. Often you will get quite a few that thin in a box of 0's. The N.A. of the objective should be no higher than .40

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