PLAN APO vs APO
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microscopeboi
- Posts: 41
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PLAN APO vs APO
hey, ive been scrounging around ebay for decent apochromatic objectives and i see that alot of them are listed as planapo or apo. whats the difference between these two? Does the planapo have sufficiently better resolution or is it trivial?
Re: PLAN APO vs APO
In essence: PlanApo is not only colour corrected, but also flat field
Be warned though ... the terminology is not very precise.
MichaelG.
Be warned though ... the terminology is not very precise.
MichaelG.
Too many 'projects'
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Scarodactyl
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Re: PLAN APO vs APO
It's not super common to find modern non-plan apo objectives. There are modern stereos that are just labeled just 'apo' so planarity might not be a guarantee, but these were greenough units (leica and zeiss) so perfect planarity might jot be expected anyway, that's not what you'd want it for. For a typical objective it seems like companies that are capable of apo optics are capable of making them flat field as well.
Re: PLAN APO vs APO
I think PLAN objectives were increasingly devoloped from 1960 on. The first apochromat was made in 1883, the first planapo in 1938. A planapo is a lot more difficult to make than a apo. The old 33mm Zeiss apos gave a very nice image but had a lot of field curvature.
Re: PLAN APO vs APO
I can second that. My Zeiss Jena 6.3x Apo is great in the centre through WF eyepieces, but not good outside 60% of the viewable area. Obviously designed for NF eyepieces, even then it would not be considered planar.
Re: PLAN APO vs APO
Are you using the right eyepiece for the objective?
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apochronaut
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Re: PLAN APO vs APO
A lot of the terms in microscopy get laid claim too, simply by the fact that the terminology that becomes part of the industry parlance gets coined and or patented by someone. A case in point is the achromatic condenser, which one company claims the invention of at a certain point in time. In fact, the achromatic condenser was being made almost 40 years prior to that but just not called such.
In the days before plan optics became a sort of standard terminology, there were various terms used to describe flat field optics. Planar, Planoscopic, Hyperplane, Flat Field were some of them. Kompensated or Compensated were used too, although those two terms usually meant mostly that there was colour and other aberration compensation going on as well.
Due to restrictions in available glass formulas, apochromatic objectives for many years needed to be overcompensated for some aberrations in order to even out others. Then, those overcompensated aspects were corrected in the eyepiece by undercompensating them. Usually there was compensation for field curvature as well, so most older apochromats are in fact "plan", if one uses the correct eyepieces. The catch is that they are only plan so far. Plan is a relative term; relative to the f.o.v. being employed. Older apochromats usually have deliberately restricted fields in order to provide a completely corrected image, because curvature correction was difficult beyond a certain point. A field of view of 12mm for 10X eyepieces is not uncommon with the best apparent fields being usually found with the 15X in any series of eyepieces. Most compensating 15's are equal to or just slightly shy of the real fields shown by their sister 10X. For this reason and also due to the usually higher inherent N.A. of apochromats, 15X eyepieces rather than a 10X are more of a default eyepiece with older apo systems. Many of them had deliberately 2mm, rather than 1.8mm high mag. objectives at 1.30 ; so 90X which when multiplied by 15X gives 1350X, perfectly within the bounds of a highly resolved image for an apochromat. So, with the right eyepieces many older apos give a decently planar image, it's just that it will be somewhat restricted in it's f.o.v. Seldom can you improve the f.o.v. with older apos with more modern eyepieces. One instance I found was using Vickers 10X compens, which have a 20mm f.o.v. with older Spencer apochromats. They mostly work , with only a slight area of overcompensation towards the periphary. Some objectives are better than others. Those Vickers eyepieces are unique.
As time marched on and glass and mathematical formulas advanced, apochromats became more internally corrected and neutral eyepieces or at least the same eyepieces used for achromats were possible and the term plan slowly entered the field. The cost involved to bring each objective to perfect correction is not insignificant, so planapos are extremely expensive. One way though, is to bring each objective to the same degree of imperfection, with various areas of correction and compensation being accomplished in a common telan lens situated above the nosepiece somewhere. This lowers the cost of production while yielding the same results and neutral W.F. eyepieces can be employed.
In the days before plan optics became a sort of standard terminology, there were various terms used to describe flat field optics. Planar, Planoscopic, Hyperplane, Flat Field were some of them. Kompensated or Compensated were used too, although those two terms usually meant mostly that there was colour and other aberration compensation going on as well.
Due to restrictions in available glass formulas, apochromatic objectives for many years needed to be overcompensated for some aberrations in order to even out others. Then, those overcompensated aspects were corrected in the eyepiece by undercompensating them. Usually there was compensation for field curvature as well, so most older apochromats are in fact "plan", if one uses the correct eyepieces. The catch is that they are only plan so far. Plan is a relative term; relative to the f.o.v. being employed. Older apochromats usually have deliberately restricted fields in order to provide a completely corrected image, because curvature correction was difficult beyond a certain point. A field of view of 12mm for 10X eyepieces is not uncommon with the best apparent fields being usually found with the 15X in any series of eyepieces. Most compensating 15's are equal to or just slightly shy of the real fields shown by their sister 10X. For this reason and also due to the usually higher inherent N.A. of apochromats, 15X eyepieces rather than a 10X are more of a default eyepiece with older apo systems. Many of them had deliberately 2mm, rather than 1.8mm high mag. objectives at 1.30 ; so 90X which when multiplied by 15X gives 1350X, perfectly within the bounds of a highly resolved image for an apochromat. So, with the right eyepieces many older apos give a decently planar image, it's just that it will be somewhat restricted in it's f.o.v. Seldom can you improve the f.o.v. with older apos with more modern eyepieces. One instance I found was using Vickers 10X compens, which have a 20mm f.o.v. with older Spencer apochromats. They mostly work , with only a slight area of overcompensation towards the periphary. Some objectives are better than others. Those Vickers eyepieces are unique.
As time marched on and glass and mathematical formulas advanced, apochromats became more internally corrected and neutral eyepieces or at least the same eyepieces used for achromats were possible and the term plan slowly entered the field. The cost involved to bring each objective to perfect correction is not insignificant, so planapos are extremely expensive. One way though, is to bring each objective to the same degree of imperfection, with various areas of correction and compensation being accomplished in a common telan lens situated above the nosepiece somewhere. This lowers the cost of production while yielding the same results and neutral W.F. eyepieces can be employed.
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microscopeboi
- Posts: 41
- Joined: Wed Apr 15, 2020 11:26 pm
Re: PLAN APO vs APO
wow! this was so helpful, thank you, i recently purchased a nikon 20x planapo objective. i have standard 10x WF eyepieces, would i need different eyepieces? your last paragraph made it seem like the standards that i have will work fine