Olympus LB Objective Question

carlh6902 · Post by **carlh6902** » Thu Sep 25, 2014 9:17 am

A question for the Olympus gurus here -

In looking over the long-barrel objectives that were availablefor the BH2 scopes, I see there were (among others) these four types:

1) A - basic achromats - not flat field
2) D - plan acromats - flat field for photomicrography
3) S - super plan achromats - flattest field for the widefield head/oculars
4) E - basic achromats - not flat field, targeted for the educational market

Does anybody know how the E objectives differ from the A objectives, in terms of their optical performance? The mechanical differences are obvious.

Carl

Charles Krebs · Post by **Charles Krebs** » Thu Sep 25, 2014 12:52 pm

Carl,

Can't answer your question since I have never used them.

You probably already have this brochure, but if not there is some basic info on pages 11 and 19.

www.krebsmicro.com/Olympus_LB.pdf

Alan Wood · Post by **Alan Wood** » Fri Sep 26, 2014 5:18 am

I have 5 different Olympus 10x LB objectives, so I have photographed a stage micrometer with each of them, using a Canon EOS 5D Mark II and an NFK 2.5x photo eyepiece to get the largest field of view that I can obtain.

Field diaphragm same diameter for all 5 shots. Aperture diaphragm adjusted for the 0.25, 0.30 and 0.40 NA objectives.

Photographed using EOS Utility on Av, exposure compensation +2 stops, each shot focused using Zoom View, resized to 1024 pixels wide in Photoshop Elements, no other adjustments.

I had difficulty focusing my SPlan 10 and the result is not as good as I expected. It is clean, so perhaps I need to buy another one.

Alan Wood

ChrisR · Post by **ChrisR** » Fri Sep 26, 2014 8:21 am

At this resolution only the EA really shows its price, perhaps. Splan is strangely brighter

?

carlh6902 · Post by **carlh6902** » Fri Sep 26, 2014 1:12 pm

So it looks to me like the "E" objectives are noticibly less flat than the "A" lenses.

Carl

ChrisR · Post by **ChrisR** » Fri Sep 26, 2014 8:04 pm

flat

Don't confuse flatness of field with field coverage. Though some objectives are flatter (more "plan") than others, many simply don't give sharpness beyond a more limited image circle. See the "field number" in the document Charles points to.
If you're stacking then the field curvature doesn't matter.
I strongly suspect the issue showing here though is lack of sharp field coverage, with the E series. That's certainly the case with some Olympus objectives I have on older student-grade scopes.

There will be "more to it" between the objectives than shows here. They all look much the same centrally. The theoretical resolution ( 0.6 * wavelength/NA) turns out to be of the order of one pixel at the size shown here. Each of the lines on the stage micrometer is only about 5 pixels wide as shown (having been reduced to fit the forum image size). In the original image where there are more pixels to look at, one would hope the more expensive objectives would show better sharpness.

Another matter of course is chromatic aberration. The "apo" objectives should be better within their designed image circle. The cheaper ones will show some CA throughout, generally increasing as you go away from the center. Some of it is "removable" in post processing of the image.