Ortholux tube lens

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Aslan
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Ortholux tube lens

#1 Post by Aslan » Mon Nov 11, 2019 10:55 pm

I was reading recently about mechanical length with regard to the Leitz Ortholux and I was wondering 2 things: 1) is the microscope useable without the 1.25x tube lens and 2), is there a tube lens that would allow the use of infinity eyepieces with the Ortholux?
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Leitz Ortholux I
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mnmyco
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Re: Ortholux tube lens

#2 Post by mnmyco » Tue Nov 12, 2019 2:19 am

I believe the answer can be found in one of my first posts, which was the same question as yours.

http://www.microbehunter.com/microscop ... f=5&t=6549

MNMyco

dawsonmic
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Joined: Tue Nov 26, 2019 3:03 am

Re: Ortholux tube lens

#3 Post by dawsonmic » Tue Nov 26, 2019 6:57 am

Hello,
There are a number of 'vintages' of the Ortholux I, and one of the things that differed the most during its almost 40 years of production (~1937 to 1976) was the design of the viewing tube. More recent instruments tended to have either the FS or FSA trinocular tubes, both designed for optimal tube length of 170mm. Most of the later FS tubes had adjustable graduated eyetubes on both sides so once the inter-pupillary distance was established, both tubes would set to the IP distance indicated. This would re-establish the correct 170mm tube length. The FSA trinocular tubes automatically compensated as the IP distance was changed. The FSA tubes are easily recognized by the IP adjustment knob location beneath the binocular portion on the right side (similar to the Orthoplan FSA head). Correct tube length is important for several reasons - in the more highly corrected objectives serious aberrations could be introduced, especially if the IP distance needed to be set near either extreme. The other issue is the parfocality of the objectives on the nosepiece. Counter-intuitively, the lower magnifications are much more highly impacted by departure from the correct tube length and you would find yourself having to move the stage significantly when switching between a scanning lens and something in the higher magnification range. The other thing about the Leitz Ortholux tubes post-war is that they are figured for a 1.25x increase in magnification as a result of the longer physical tube length required by having the switching system between the photo tube and the binocular. The tube lenses are introduced in order to make the optical corrections to the objectives so they respond properly to the longer physical length. So the short answer is that, yes, the tube lens should be used. If you are using simple achromat objectives and do not mind having to refocus in the lower magnification range you could probably make do without one.
Leitz made several versions of the 1.25x tube lens. Earlier versions were not especially well-corrected for the more recent wide field ocular (GF series), so they introduced a 'W 1.25x' version, which is distinguished by the addition of the 'W'. Regarding the use of infinity objectives on the Ortholux I, it is possible as Leitz objectives for industrial and metallurgical use were mostly infinity-corrected. The main difficulty would be finding an orphan infinity tube lens as they were usually only installed in the metallurgical vertical illuminators (both 1x and 0.8x versions were made). But if you are trying to use the metallurgical Leitz objectives with biological material with a cover slip, then the infinity lenses will not work as they are corrected for use without cover slip. With the lower numerical aperture lenses (say, 0.25 and less) you could probably get by using them in transmitted light along with a cover slip, but at higher numerical apertures you would introduce severe problems. I have never tried using infinity biological objectives from a different manufacturer with an infinity-equipped Ortholux I nosepiece, but I would think it would be possible although the magnifications might not be exactly as denoted on the objective (even with the 1.25x factor taken into account).
Someone else had referenced a post in which their Ploem fluorescence vertical illuminator was fitted with an infinity tube lens, but that highly unusual (being a biological vertical illuminator for cover-slipped specimens, it had a special 170mm tube lens). Perhaps someone had installed one of the infinity lenses in his illuminator. The problem with doing so in a biological vertical illuminator is that it would throw off the positions of the field and aperture diaphragms, as the collector lens in the Ploem illumination light path would be incorrectly focused. I would be curious to know how his Ploem system is configured.
There were two other 'standard' tube lengths for objectives that would have been of the Ortholux vintage. The Ultropak were corrected for 185mm, but since they use special change rings and vertical illuminator that had the correct tube lens installed, the user need not worry about having to change anything. The other tube length was for the objectives used with the incident light pol-vertical illuminator. Those were corrected for 215mm tube length and had to be mounted into special centering change rings.
Hope this helps!
Cheers,
Dave P.

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wporter
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Re: Ortholux tube lens

#4 Post by wporter » Tue Nov 26, 2019 5:14 pm

Thanks for the very comprehensive info, Dave P.

I know many the later (1980s) 160mm TL Leitz scopes used FSA heads also, although they often had a dash with some additional letters, indicating particular models with different features. Is that when the the 42mm head mount came in? ( versus the earlier 43mm mount.) Also confusing is the fact that many or most of the heads don't have the FSA designation anyplace on them, just sometimes the part number.

Aslan
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Location: Toronto

Re: Ortholux tube lens

#5 Post by Aslan » Thu Nov 28, 2019 2:14 pm

Thank you for the very informative responses. I have abandoned the plan to use infinity lenses on the Ortholux and just stick to what I can easily use.
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Leitz Ortholux I
Leitz SM microscope
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Spenser 58 convertible microscope

Sabatini
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Re: Ortholux tube lens

#6 Post by Sabatini » Wed Dec 11, 2019 2:05 am

Thank you very much to all for so interesting information, I already put more clear my ideas to get the most out of my beloved Ortholux.

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