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Macrero
Joined: 01 Sep 2011
Posts: 104
Location: Valladolid , Spain
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 Posted: Wed Apr 18, 2012 2:31 pm Post subject: More questions about tube lenses and "infinity" |
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I'm waiting a couple of "tube lenses", which I bought : an Apo-Gerogon 9/150 and G-Claron 9/210 , and still mulling over the issue of "infinity" objectives and tube lenses ... I wonder : if the aberrations are corrected in the objective , Is it necessary an Apo lens ?? as far as I know, in the Nikon infinite systems correction is made entirely on the objective , and the tube lens is "neutral" ie it makes no any correction , then will there be any benefit of using a Apo lens ? or maybe some negative effect ? I doubt the latter, but apparently this is still a world to discover , and the best way to tell is to try ...
Another thing : in the infinite systems of both Nikon and Olympus, there is a significant distance between the objective and tube lens , and I read somewhere that this distance is very important in achieving optimal quality , but I've seen that all (or almost all) use the objectives very close to the tube lens , I guess to avoid vignetting , Does this affect quality ?
Kind regards ! |
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Charles Krebs
Joined: 01 Aug 2006
Posts: 4072
Location: Issaquah, WA USA
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| Posted: Wed Apr 18, 2012 4:38 pm Post subject: |
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While Nikon CF, Mitutoyo, (and current Olympus UIS objectives) make all color corrections in the objective only... it may be best to think of it more like this:
All of the chromatic correction that the designers intend to make for that particular "level" of objective are corrected in the objective. Apos are most certainly much more highly corrected than achromats for a wider range of wavelengths. But this comes at a much higher complexity and cost. In order to meet a variety of price points (among other more practical reasons) the big manufacturers typically offer at least three "levels" of objectives. And typically the price goes up considerably depending on the designed degree of correction.
Here is some info from manufacturers....
from web page: http://www.olympus-ims.com/en/microscope/terms/feature12/
some Zeiss info
from http://photonics.intec.ugent.be/education/IVPV/res_handbook/v2ch17.pdf (A worthwhile PDF to download)
And from http://www.microscopyu.com/articles/optics/objectiveintro.html
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Peter De Smidt
Joined: 05 Jan 2012
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rjlittlefield
Site Admin
Joined: 01 Aug 2006
Posts: 12577
Location: Richland, Washington State, USA
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| Posted: Wed Apr 18, 2012 11:09 pm Post subject: |
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| Macrero wrote: | | I wonder : if the aberrations are corrected in the objective , Is it necessary an Apo lens ?? as far as I know, in the Nikon infinite systems correction is made entirely on the objective , and the tube lens is "neutral" ie it makes no any correction , then will there be any benefit of using a Apo lens ? or maybe some negative effect ? I doubt the latter, but apparently this is still a world to discover , and the best way to tell is to try ... |
Macrero, Charlie has given great information about the objectives themselves, but I interpret your question as asking about the tube lens.
It is a good question. I'm not sure about the best answer.
As diagrammed HERE, the rays used by an objective & tube lens combo will be slightly different from those that would be used by the tube lens alone, stopped down by its own aperture.
So, even though Lens A beats Lens B in looking at infinity, it does not necessarily follow that Lens A will beat Lens B when used as a tube lens.
As an example, see HERE. The test is clear that Canon's 55-200 EF zoom is significantly more crisp at f/10 than is Mitutoyo's MT-1 tube lens. But I certainly would not expect that the zoom would actually do better than Mitutoyo's own tube lens when used in combination with Mitutoyo's objectives.
| Quote: | | Another thing : in the infinite systems of both Nikon and Olympus, there is a significant distance between the objective and tube lens , and I read somewhere that this distance is very important in achieving optimal quality , but I've seen that all (or almost all) use the objectives very close to the tube lens , I guess to avoid vignetting , Does this affect quality ? |
Significant separation between objective and tube lens is needed to insert additional optics such as beam splitters and filters.
Presumably the official tube lenses are designed to provide the best possible performance given that separation. It is unclear whether they would degrade given less separation.
For the Mitutoyo, my test linked above was done with only about 15 mm separation between the iris and the tube lens, and still the tube lens performed admirably.
When lenses designed to be used by themselves are pressed into service as tube lenses, I would expect off-axis performance to degrade with increasing separation, due to the increasing use of rays that the "tube lens" might not normally use. See HERE for further discussion of that issue.
--Rik |
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Macrero
Joined: 01 Sep 2011
Posts: 104
Location: Valladolid , Spain
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| Posted: Thu Apr 19, 2012 1:36 am Post subject: |
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Charles : This is what I had thought , that the Apo lens would help to eliminate residual aberrations . I obviously will make test of all kinds , but wanted to know your opinion and experience . Thank you Charles !
Peter De Smidt : Yes, I know, but I do not think this affects the image quality in this case. I have long used the G-Clarons , and they are excellent performers , not only at short distances , which is for they are designed , but also at infinity , and although Schneider not called it "Apo" , they are very well color corrected . But apparently , mediocre lenses (see "morfanon") work very well, and some good lenses not work as well . What will be G-Clarons performance as a tube lens ? When I try , I'll tell ...
Rik : Thank you for your answer helped me to clear my doubts, again . I hope to have soon the tube lenses and make some tests .
Thank you all!
Kind regards ! |
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