PlanApo 60x/1.40 objective acquired

This is another milestone for my reverse engineering work.

60x objective
Olympus PlanApo 60x/1.40 Oil objective


The resolution power of this objective is slightly better than my 100x/1.25 objective, but the field of view is 1.67x wider.

Which means, 2.72x more area per image.

So, in theory, a 21 hours capture like this ATMEGA8 should go down to less than 8 hours.

The theorical resolution power of this objective is supposed to be about 220nm using a 500nm green light, but in practive the best resolution is achieved only if you use a 0.17mm thick coverglass.

A perfect objective for reflected light would have been a ∞/- one, but at least I can also use this one as a bio objective.

Examples

Here two demos with some post processing to fix chromatic aberrations caused by my reduction lens, but also the 100x that is not apochromatic.

I’m using a FMA050 reduction lens attached to a FC300 camera, and 1.25x zoom on the olympus magnification changer.



PlanApo 60x/1.40 Oil - ATMEGA8 M1/M2



Plan 100x/1.25 Oil - ATMEGA8 M1/M2


Here are two images with corrected CA.

You can also see the original images without any post processing, and with focus stacking for comparison.

There is some slight CA on the 60x because of the reduction lens.



Olympus PlanApo 60x/1.40 Oil
Original | Stacked



Olympus Plan 100x/1.25 Oil
Original | Stacked


Note: I use the same exposition for the 60x and the 100x.

Coverglass and resolution

This objective requires a coverglass of 0.17mm thickness, as noted at the bottom (∞/-).

Oil have a refractive index of 1.51 and borosilicate glass a RI of 1.51446.

The difference is very small, but at high N.A. this can cause spherical aberrations. Basically, the image will appear less sharp and so this is equivalent to a loss of resolution.

My main concern was to check if the resolution was good even with no coverglass. Or at least not less than the 100x objective.

1 2 3
60x with coverglass 60x without 100x/1.25

The left image was using a cheap coverglass of 0.13-0.17mm.

We can clearly see a difference between the first and last image.

We can also see that the first image is sharper than the second. So the lack of coverglass is indeed degrading resolution. But it’s relatively small and the resolution is still better than the 100x.

Note: Ideally it would have been necessary to use a #1.5H coverglass, which is equivalent to 170 ± 5 µm thickness.
I don't have any so consider the result as non optimal.


Resolution in blue wavelengths

One of the wonders of apochromatic objectives is the image quality with blue wavelengths.

Here we can clearly see a gain of contrast and resolution.

TLDR

  • Resolution is better than the 100x/1.25 even without coverslip
  • Resolution in the blue wavelengths is much better
  • Contrast is better
  • The field of view is wider, with 2.72x more visible surface
  • Optimal performances requires a coverglass