Objectives, Probably a dumb Question.

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GerryR
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Objectives, Probably a dumb Question.

#1 Post by GerryR » Thu Jun 23, 2022 3:08 pm

It seems that there are two "standard" industrial parfocal lengths used, 45mm and 60mm. AO Spencer used 34mm. Can spacers be used to adapt a shorter parfocal length objective to a turret with longer parfocal length objectives? For example, 11mm spacer with 34mm parfocal objective to obtain 45mm length. I don't know enough about optics to know why or why not, but do realize enough to know not to mix infinity objectives with fixed tube length objectives.

PeteM
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Re: Objectives, Probably a dumb Question.

#2 Post by PeteM » Thu Jun 23, 2022 3:42 pm

With "infinity" objectives, such as the 45mm parfocal Olympus UIS, you could add a 15mm spacer (with an RMS to 25m thread adapter) and use it on a Nikon CFI060 system with 60mm parfocal distance. So, yes, you can extend somewhat shorter infinity type objectives a bit and get them parfocal with longer ones.

The next question is if there are different corrections for things like field flatness and various aberrations in the infinity microscope tube lens? In this case the newer Olympus has few if any corrections there and the Nikon claims every thing is handled in the objective - so you'd get a good image.

The older 34mm American Optical objectives can also be put on an 11mm spacer to make them parfocal with their later 45mm infinity objectives BUT the tube lens (at the bottom of the head) corrections between the two series of lenses are different. You'd be parfocal but see some aberrations - maybe more visible to a camera than the casual viewer.

With "finite" objectives, the tube length was standardized to 160mm a while ago -- but some are 170mm, 210mm etc. and with different places for the eyepieces to pick up the image. The various makers' objectives will have had all sorts of parfocal distances from about 33mm to 45mm - with 45m being pretty much the standard that was settled upon. In addition, most legacy systems require eyepieces with a "C," "K," etc. to correct or compensate for optical aberrations. A few makers (Leitz, for example) made adapters with a lens in them to allow upward compatibility from a shorter to a newer longer barrel objective.

Not only do you not want to mix finite and infinite objectives - for finite systems you generally want to stick with the the objectives and eyepieces intended for the microscope - or perhaps switch everything over to a newer set of optics if the microscope has room to fit them.

apochronaut
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Re: Objectives, Probably a dumb Question.

#3 Post by apochronaut » Thu Jun 23, 2022 5:39 pm

With infinity corrected objectives you can lengthen them to achieve parfocality but all telan lens systems are different. Despite the belief being around that this maker or that maker corrects everything in the objective and another doesn't, the telan lens is called upon for certain corrections too and some manufacturers choose to install certain aberrations into lens systems in order to more easily correct others in another. AO for instance had complete peripheral ca correction in the 60's within the context of the various objective classes but chose to abandon that in their later system. It is hard to know why exactly but an overlooked factor in wide field systems is field flatness and also economy of production. All modern infinity objectives have a colour correcting and field flattening rear lens group but it may be more cost effective to install some of that into the telan lens and or eyepieces.

In manipulating 4 infinity systems around across 4 platforms( 6 if Jena and Lomo are jncluded but they are wholly different) I find that there are real if sometimes subtle differences in the duty placed on the telan lens. Manufacturers make microscope systems to have as little aberration and distortion as possible right across the field. In installing non native or altered objectives in a system, sometimes it is acceptable to have a small percentage of mismatch that results in an almost imperceptible level of peripheral aberration but ideally it isn't.

The easiest way to utilize infinity objectives across platforms is to adjust your final image with the eyepieces. While it is cumbersome but possible to have two brands of objectives in a nosepiece and swap eyepieces for each brand, it is also possible to have two brands of objectives in a different brand stand which are well corrected by a different brand eyepiece. A case in point is a current settup I just put together if only to do a comparative evaluation of a newly hatched objective.
The stand used was an AO from the 60's, the head was AO Reichert from the 80's, the objective is a new Indian made Plan fluor, tested against a Chinese made PlanF , a Reichert Planachro and a Reichert Planfluor ; all of them 40X. While the image through the Reichert objectives is perfect utilizing the factory Reichert eyepieces, the other objectives in Olympus infinity format suffer from some peripheral ca. The eyepiece solution turned out to be a pair of 22mm f.o.v. Nikon opthalmic 12.5X eyepieces which bring both systems so close to being peripherally perfect that one could build a dandy 22 mm f.o.v. 1250X planfluor microscope on that aged AO 10 platform and have a microscope for about 700.00 that would perform very close to a new $5,000.00 microscope.

GerryR
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Re: Objectives, Probably a dumb Question.

#4 Post by GerryR » Thu Jun 23, 2022 6:49 pm

Thank you, both. Some very interesting insights for me to ponder!

LouiseScot
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Re: Objectives, Probably a dumb Question.

#5 Post by LouiseScot » Thu Jun 23, 2022 7:52 pm

You can get adapters which allow fitting a Nikon CFI60 objective to a 45mm RMS holder. Unfortunately, it might be problematic trying to fit a CFI60 objective in place of a 45mm one simply because there may not be sufficient space between the objective holder and the slide. It's a bit annoying when that happens! Nikon brought out the Eclipse series for CFI60 objectives https://lavinia.as.arizona.edu/~mtuell/ ... clipse.php

Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

GerryR
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Re: Objectives, Probably a dumb Question.

#6 Post by GerryR » Mon Jun 27, 2022 8:20 pm

I was able to get a 20x AO Spencer C80874 objective to fill the gap in my 160/0.17 objectives (10x, now 20x, 40x,100x) and decided to try it in my AO Sixty infinity scope just for kicks. Low and behold I was able to get a perfect image on this scope. It was .014" short for parfocal to which I added a spacer ring so it is parfocal with the rest of the objectives. Centering is off somewhat but not enough to worry about. It is my understanding that AO used a 160 mm tube length for their earlier infinity scopes. Is this why this objective "works" in this scope? The field seems flat and image undistorted. What anomalies can I expect with this objective in this scope?

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Re: Objectives, Probably a dumb Question.

#7 Post by blekenbleu » Mon Jun 27, 2022 8:41 pm

GerryR wrote:
Mon Jun 27, 2022 8:20 pm
What anomalies can I expect with this objective in this scope?
One beauty of infinity objectives is that tube length mismatch mostly affects magnification factor.
With suitable high contrast rectilinear targets, chromatic, spherical and other aberrations may be evident,
particularly in camera images (depending on photo relay lens correction mismatches).
Optiphot 1, 66; AO 10, 120, EPIStar, Cycloptic

GerryR
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Re: Objectives, Probably a dumb Question.

#8 Post by GerryR » Mon Jun 27, 2022 8:51 pm

blekenbleu wrote:
Mon Jun 27, 2022 8:41 pm
GerryR wrote:
Mon Jun 27, 2022 8:20 pm
What anomalies can I expect with this objective in this scope?
One beauty of infinity objectives is that tube length mismatch mostly affects magnification factor.
With suitable high contrast rectilinear targets, chromatic, spherical and other aberrations may be evident,
particularly in camera images (depending on photo relay lens correction mismatches).
The C80874 lens is supposed to be a finite lens for 160 mm tube length. I checked the magnification while in the infinity scope, and it is 2x the 10x objective. Did I just luck out??

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blekenbleu
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Re: Objectives, Probably a dumb Question.

#9 Post by blekenbleu » Mon Jun 27, 2022 10:43 pm

GerryR wrote:
Mon Jun 27, 2022 8:51 pm
The C80874 lens is supposed to be a finite lens for 160 mm tube length. I checked the magnification while in the infinity scope, and it is 2x the 10x objective. Did I just luck out??
Objectives < 20X are less fussy than those > 20x; I use a finite 4x as finder on an AO 120 (infinity).
Optiphot 1, 66; AO 10, 120, EPIStar, Cycloptic

apochronaut
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Re: Objectives, Probably a dumb Question.

#10 Post by apochronaut » Tue Jun 28, 2022 10:36 pm

GerryR wrote:
Mon Jun 27, 2022 8:20 pm
I was able to get a 20x AO Spencer C80874 objective to fill the gap in my 160/0.17 objectives (10x, now 20x, 40x,100x) and decided to try it in my AO Sixty infinity scope just for kicks. Low and behold I was able to get a perfect image on this scope. It was .014" short for parfocal to which I added a spacer ring so it is parfocal with the rest of the objectives. Centering is off somewhat but not enough to worry about. It is my understanding that AO used a 160 mm tube length for their earlier infinity scopes. Is this why this objective "works" in this scope? The field seems flat and image undistorted. What anomalies can I expect with this objective in this scope?
AO used 182mm for the 34mm parfocal infinity but that 182mm is the reference focal length : the distance between the telan lens and the top of the eyepiece tube. The actual length between the objective shoulder and the top of the eyepiece tube or in other words the distance covered by a 160mm tube is actually around 270mm but due to the telan lens creating the intermediate image, the actual magnification of a finite tube objective seems to take place only over the reference focal length. A 20X finite tube objective would give 22X and a bit in an AO 10 for instance.
One set up I use is a Nikon 160mm tube 100X glycerin immersion objective in an AO/Reichert infinity stand and it magnifies about 110X, so pretty consistent with the above.
The 60 is a quirky scope. I don't have a lot of experience with them but oddly, I have seen them with both infinity marked objectives in them and ones marked without an infinity mark. The cat.# 1127 objective they used in them, is 97X and looks an awful lot like the 160mm 97X. I have seen it both marked with an infinity sign and without. It is entirely possible for 160mm objectives to work in an infinity scope and it seems likely that the length of the infinity space is a critical factor in that. Some work well like my Nikon 100X and some are dreadfull.
Possibly, the 60 , being an early infinity student scope, was made so that both infinity and 160 objectives would work passably, so schools for instance could economize and utilize existing 160mm optics. The scope had no accessories for the infinity space that I know of, so they could put whatever length infinity space they wanted to in it.

I have tried the later generation of 160mm objectives in an AO 10 and they do not work well. They focus a little close and while the image is flat and within magnification tolerance( 13% high) with no overt ca, the spherical aberration is really high, thus giving a low contrast, milky appearance to the image with lousy resolution. Totally unusable.

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