MicrobeHunter.com Microscopy Forum

I'm wondering which Chinese 160 mm objectives to choose for cheap epi-illumination to minimize back-reflections: achromats or planachromats?

Achros have fewer lenses (less back-reflection), but planachros probably (just my guess!) have better anti-reflection coatings, since they're a higher class product. Thank you!

Probably not a huge difference I would guess.

jjtr1 wrote: ↑

Sun Jul 03, 2022 4:51 pm

I'm wondering which Chinese 160 mm objectives to choose for cheap epi-illumination

Consider instead objectives with narrower noses and greater working distance,
to allow for illumination from e.g. 40mm LED Halo Rings
https://www.amazon.com/gp/product/B01FWX19QS
for nominal darkfield illumination:

Objectives for my metallurgical scope are plan, with longer working distance. It works well. Objectives are 4, 10, 20 and 50x.

Typically, plan optics provide better overall peripheral correction for more than just curvature of field but they are not all the same . A really good plan system should have peripheral ca, sa, coma and astigmstism under control too.

Non plan optics are variable as well, with some having very poor peripheral correction for aberrations and distortions and some approaching or achieving semi-plan performance without really saying so. Higher magnification objectives suffer more from aberrations and distortions due to the heavy curvatures of the lenses required.

It probably depends heavily on what the nature of your sampling is. If you are viewing a lot of uneven samples with depth and your achromats are only well corrected over the typical 35% of the center of the field , having full planarity will improve the imaging only a little because your visual field doesn't see any more than the corrected field of the objective, usually less. You will have to move the sample anyway, to center it for viewing.
If you are viewing flat polished metallurgical samples or other quite flat samples such as electronics, plan or nearly plan optics may be in order.