I like those images, especially the last two from the first image set. I have an old Perfect brand prepared slide of pond plankton made in the '60s, and one of the objects looks a lot like those last two images. Are radiolaria found in fresh water?
nice images! Since radiolaria have no colour you might just use one colour channel (I think green is best) of your image so you effectively come close to the image quality of an apochromat. I like to use round cover slips for permanent slides because it is much easier to get a good looking slide with them. Octagonal cover slips would be nearly as good but probably cheaper to make but I have never seen them.
I once bought chinese round cover slips from ebay (what can be wrong with them ?
) but they were complete rubbish as the were up to 0,25mm thick.
I got mine from a woman at the german forum, originally bought from some lab supplier.
That got me to thinking, that I've never checked the thickness of the 1400 Chinese made 18mm round coverslips that I bought about 10 years ago from an Ebay seller of Chinese microscopes and accessories based in southern California. At that time, 1000 of these coverslips cost about $30. Now the price is over double that from any source I can find.
I got out my trusty old Brown & Sharpe vernier micrometer, that measures to .001 inch with the vernier scale giving readings of .0001 inch. I pulled out about 8 of these coverslips from the little plastic box and measured them. They varied from .0058 to .0062 inches, or roughly .15 to .16 mm.
Checking again, it looks like two purchases were made from different sellers, most of the cover slips are "Sail" brand, and a few boxes are "Pearl" brand. I think the ones I checked were Sail brand. Boxes from both brands show a thickness range from .13 to .17mm.
Most of the slides I've mounted with these coverslips are viewed with the lower power objectives, seldom higher than 20x. I guess it would be a good idea to check the thickness of any coverslips that will be used for high power observation.