Excellent Vickers D.I.N. 40x .85 for sale.

[apochronaut]

I am not associated with this auction and I do not know what the reserve is but this 40x .85 Vickers D.I.N. objective could be a fine beginning to upgrading a basic 160mm D.I.N. microscope, if the price ends up being in line. It is not 170mm, as stated in the auction. I use a 40x .70, on occasion and Vickers optics have outstanding contrast and resolution ; easily the equal of any other 160mm tube optic made. The same objectives can be found under the name Cooke-Baker, which the Vickers Instruments microscope division was branded as, prior to 1963.
http://www.ebay.com/itm/Vickers-England ... Swz5ZZuby5

[KurtM]

Does this lens require oil or water immersion to attain that NA? Or if not, then why aren't more 40/45x objectives higher NA than ~.65?

Maybe the answer will help me understand NA better...

[apochronaut]

It is a dry objective.

40x .65 objectives provide an ideal balance of resolution and offer flexibility, when it comes to getting decent imaging with variable sample thickness. Coverslips of variable thickness are accommodated with minimal spherical aberration, so .65 objectives fit well into most average situations, where critical control of the sample thickness might be difficult or where prepared slides of variable thickness might be encountered. The N.A. is also high enough that 15x eyepieces can sometimes be used to provide more detail. This latter capability is more often the case with objectives made by the better makers, which provide better contrast, colour correction and sharpness.

The jump to a .85 objective, limits the sample thickness flexibility, while providing better overall resolution. Usually a variability of only .002 mm will begin to induce some spherical aberration but the resolution will still often exceed that of a .65 objective at that point, falling off eventually, as the sample thickness departs from the ideal, to the point where a .65 objective can have better resolution with very thick samples. Usually, however, a .85 objective will attain a cramped working distance about the same time that it's performance starts getting checked, for they always have a shorter working distance than a .65 from the same family , which puts a physical limitation on the sample thickness.

Higher N.A. objectives can sometimes have a shallower depth of field too but this is dependent on the sophistication of the optical design .

It seems that both a 40x .65 and an objective of a higher N.A. might be the way to go for some microscopists, offering the best of both capabilities.

There are L.W.D. high N.A. objectives though. One such, I am familiar with, is an AO/Spencer L.W.D. S.F. 43x .85 achromat, which was made for the series 2/4. This is an objective which is a joy to use, having a working distance that exceeds that of the more conventional AO achromats of the period, yet provides superior imaging too. I have only ever seen the one I have, so they must not have made too many of them.

A higher N.A. objective, usually attains it's performance due to the use of some fluorite glass or other similarly performing low dispersion glass, thus they also usually have better colour correction, with some attaining close to fluorite performance. It is normal for 15x eyepieces to be used to gain more detail and in some cases , 20x eyepieces as well, occasionally allowing one objective to do the duty of 2 .

Higher N.A. objectives generally require more critical precision when it comes to the use of coverslips and the preparation of samples, culminating in the necessity for correcting collars on very high N.A. dry objectives. They also are unforgiving of poorly made prepared slides.

[georgetmacro]

Apocronaut ... going by what you are saying what does this mean for the likes of one of the a apochromatic lenses that I am experimenting with i.e., a Carl Zeiss Jenna 40X / o.95. I know this is a extremely sharp objective but seems to have an extremely narrow depth of field ... it is a 190 mm tube-length objective that I am attempting to adapt to use on a 160 mm instrument. Is it normal for objectives for this tube-length to have higher NA than that of one made for 160 mm tube length.

[apochronaut]

There is no relationship between the tube length that an objective is corrected for and it's designed N.A. Low dispersion glass is required to achieve higher N.A.s, which at the time that your objectives were made,usually meant optical fluorite. The more use of low dispersion glass, meant that the design could be optimized for a higher N.A. and better performance, so a semi-apochromat or apochromat objective was the result.

Most of the older established companies, made several series of objectives designed for the same application ; achromats, fluorites and apochromats, leaving it up to the customer, which design met with their needs or they could afford to buy.