Further tests with repaired Spencer 1.4 N.A. objective.

[apochronaut]

Subsequent to making the condenser in this thread viewtopic.php?f=12&t=1173&hilit=condenser+quest, I made an apochromatic condenser in an identical AO/Reichert 1973A condenser shell. Until recently, I had only trialled both as dry condensers but I decided to test them with the newly repaired Spencer 1.4 N.A. objective , profiled in the recent thread
viewtopic.php?f=5&t=7167&p=63410#p63410

Additionally, I have now acquired a factory AO/Reichert 1973 1.4 N.A. achromat/aplanat condenser.
I took one picture of a Cymbella diatom through each oiled condenser plus one picture through my original D.I.Y. condenser unoiled.

1) unoiled D.I.Y. condenser koehler adjusted, probably around .95 N.A.
2) oiled D.I.Y. condenser Koehler adjusted, N.A. unknown but built with a 1.4 N.A. front lens.
3) oiled D.I.Y. apochromat condenser. This design cannot be Koehler adjusted due to a longer focal length then necessary to do so. same N.A.
4) oiled 1.4 N.A. achromat aplanat condenser Koehler adjusted.

[apatientspider]

Maybe it's just my old eyes, but in most "un-helped" photos of diatoms the little dots never appear very sharply focused to me. However, I think these images of a diatom taken through the repaired objective are at least as good as any simple brightfield images of diatoms I've ever seen posted on these forums. Again you don't say whether or not the objective is also immersed here. But even so, the fact that this is a superior lens certainly seems to show.

That is not surprising actually when it's considered that when this lens was made in the last half of the 1920s it sold for about $85. Consider the fact that in those days $85 would also buy four and a quarter ounces of gold. What would that much gold cost today - about $5000 ? And how likely is it that an amateur or hobbyist could afford such a lens? It was pretty much state-of-the-art when it was made, and yet it still compares favorably with lenses made today nearly a hundred years later.

Thanks again, Phil, for your expertise and persistence - and maybe just plain stubborness in resuscitating this jewel for me.

Jim

[desertrat]

Very impressive images from a repair job that few people could do successfully.

It helps me appreciate my antique 1.25 N.A. fluorite, even though it's not in the same class. I still enjoy using it occasionally.

[apochronaut]

Thanks to both. Yes, Jim the lens was immersed and I used heavy immersion oil....the kind recommended for inverted microscopes.
You might consider using that with this lens, Jim. It is impossible for me to tell for sure, whether the seal around the front element is complete. It should be but just in case there is a tiny pore or seam through which oil might eventually creep, using the heavier oil might mitigate that chance, somewhat. It is a very nice lens. Slightly low in contrast by my standards but then I find older apochromats to seem that way relative to achromats. Achromats create a false contrast by causing diffraction banding and apochromat images can seem pale or a bit bleached with some samples in comparison.