Parasitoid

[CharlesT]

Taken with a button-lens :

It looks to be a single element, so maybe one cannot get an objective more primitive than this :-)

[Lou Jost]

Nice picture, but what is a button lens?

[CharlesT]

Apologies; 'button-lens' is not a technical term .... it is a (slang?) description for a microscope objective that has the same sort of shape as a clothes button.

[rjlittlefield]

Heh, I had assumed you were talking about a CCTV lens made to look like a button, something like THIS.

I expect those might actually work sort of OK, reversed of course, because they're designed to play well with a small array of tiny pixels on the back side.

--Rik

[Lou Jost]

I still really don't understand what this objective might look like

[CharlesT]

Maybe the one at the top left is not very button-like but the images for the stack were taken with a Cooke-Baker objective much like that (Vickers) one.

Perhaps it is simply the lack of a shroud that make them feel primitive.

[Lou Jost]

Thanks. I didn't know there were such simple objectives. And I would never have guessed they would give such nice results as you got!

[CharlesT]

Lou, your expectations are actually correct... I forgot to mention that the picture had Local Contrast Enhancement
So it should be 'Old button lens plus LCE'
So my description is a bit misleading

On the other hand, maybe it is an opportunity to highlight that LCE does brighten up the images from old objectives ? :
The Local Contrast Enhancement plugin, written by Tanel, for paint.net, works well ... For settings; 'Smoothing' set to zero, 'Radius' around 12, 'Amount' just below where it is too noticable, often seems to be the starting point for my Canon at low magnifications.

[Downloading Paint.Net, from a web search is a bit of a minefield, for some reason. Starting here; https://www.getpaint.net/download.html is reasonably safe, but still be careful about clicking on the wrong item].