20x Achro obs question

[cpsTN]

As with many others, my scope (Amscope M500B), has 10x and 40x objectives, amount others. I know the working distance of the 10x is large and "friendly" and that of the 40x is very small, less than 1mm. Where does the working distance of the 20x fall relative to those of the 10x and 40x? Is it midway between them or is it logorithmic? I referring to achromatic DIN objectives.

Charles Sands
Murfreesboro, TN

[zzffnn]

http://www.olympusmicro.com/primer/anat ... tions.html

About midway. Typical WD of typical 20x NA 0.4 is around 3mm (about half of 10x NA 0.25 's 6.10mm , while 40x NA 0.65 has WD of around 0.45 mm). If you have a high aperture 20x NA 0.65, then estimation based on NA would be safer.

[cpsTN]

Since your post, I bought an Achromatic 20x NA 0.40. The link was helpful. One question though: Since NA is an angle, would the WD be smaller with an NA of 0.65 compared to that of 0.40? Interesting to think that the WD of the 20x is almost 7x the WD of the same 40x!

Charles Sands
Murfreesboro, TN

[zzffnn]

Typically:

WD of NA 0.4 is around 3mm
while NA 0.65 has WD of around 0.45 mm

Magnification has very limit (<10%) impact on WD. NA is the major (~90%) factor.

[apochronaut]

If I can add this. W.D. , although it refers to a measurement of free space between the objective and the surface or coverslip does mean working distance, otherwise it would be called " clearance". Lower power objectives , up to about 20X are made by some companies with tapered barrels, so 1) incident illumination is easier to accomplish with uniformity and 2) physical manipulation of the subject is easier. These become less of a factor , as the magnification increases. Once the N.A. climbs much above .50, the W.D. becomes negligible in practice, unless you have a micromanipulator.

[cpsTN]

The term "clearance" makes more sense, although you see the term "working distance (WD)" all the time. I DO have a micromanipulator, but enough about my wife. lol