MAYBE THIS SHOULD BE IN BEGINNERS CORNER but....

[wmodavis]

It has been a while since posting here but I assure you that I peruse almost daily for topics of particular interest. But today I'm back for some expert advice. Having two Olympus BH2 scopes and still being on the steep side of a learning curve, and thinking I might be ready to go for a new lens having looked around a bit but a detail has been confronting me requiring input. Most of the lens I have obtained, many through ebay, are decent DPLAN series with a couple others including an SPLAN 40x. I was impressed with what seemed to me to be an improvement in viewing through the SPLAN. I also have a DPLAN 40x in the turrent right beside it and repeated comparisons seem, more often than not, to cause me to prefer the SPLAN. This was NOT a double blind placebo controlled test so I could be deceiving myself.

Anyway getting down to the question at hand...

I think I might be ready to go for another jump in quality but there is a cost involved that makes me mildly queasy to jump out of the plane without rechecking mu parachute. I've been looking at SPLAN APO yes apochromatic and as I learned from you all early on they are good but pricy. I do see that they are pricy but have not as yet put my eyeball through one to determine how/if I would be impressed about the "good" part but think as I said I might be getting close. A choice in options between a lens designated with or without the NC (no cover) begs more understanding. So, actually & finally getting down to the question,

"What are the up and down sides of a lens designed to be used without a cover glass? OR what can you do with them and what can't you do with a NC lens?

It looks like the APO may be a $400-$600 paypal burden so just want to know before I plunk down and I don't want to regret it.

I look forward to all opinions on this.
Thanks
Bill

[Crater Eddie]

Bill,

From my recent similar comparison between 10x and 20x DPLAN and SPLAN objectives (which I assume you have read), I agree that the SPLAN's seem to give a sharper, more pleasing image. I too would like a nice set of SPLAN APO's, but I'm not likely to make that kind of cash outlay any time soon. I'll be very interested in your experiences here if you decide to go down this road.
If I was doing hematology work I might want a 40x NC objective for scanning blood smears without the bother of a cover glass. For home hobby use I can live without it.
Just my 2 cents.
CE

[Tom Jones]

CE,

We never had NC objectives in the hematology labs I've worked in, and never used cover slips on non-permanent slides.

We always spread a drop of immersion oil across the dried blood smear for low magnification to eliminate the diffraction caused by the dried cells. If, after we added another drop of oil and went up to 100x, we needed to go back down to a 40x dry objective, we simply used a glass rod to wipe off the excess oil and make the film thin enough it would get on the end of the dry objective. The thin film of immersion oil substitutes rather nicely for the cover glass. I had a pathologist for awhile who liked to use a cover slip on top of the drop of oil, but he's the only one. I think he wanted to be sure he didn't get oil on his 40x.

Then along came 40x-50x oil immersion objectives and life was much easier!

Tom

[charlie g]

Hi, I think Tom ( thanks for the practicle and specific use your lab used microscope NC techniques with subjects)...I think Tom draws attention to: 'what type of specimens are you intending to observe with NC objectives?'.


I dropped approx $600 for a Nikon 60X plan apo...it's great...but I have it in cigar box awaiting certain specimens.

NC objectives totally rule out a lot of higher magnification specimen observing.

charlie guevara

[Crater Eddie]

Tom Jones, I'll admit that lab was several years ago for me. Its always interesting to hear how different lab do / did things.
CE

[wmodavis]

CE - Wondering why "NC objectives totally rule out a lot of higher magnification specimen observing."

I likely (if at all ) will only get one of these so have to be pretty selective and evaluate my intended use presuming I even know that. Maybe just getting adventurous.

I can & do have other things to spend the money on like clutch repair on my truck currently in the shop but...

It would give some notoriety to be the only one on my block to have a PLAN APO. That's worth something isn't it?

[apochronaut]

The corrections on coverslip corrected objectives and no coverslip objectives are quite specific and are specified as such to keep spherical aberration to a minimum. Crossing over is possible with lower N.A. objectives. This is why some objectives have a little - after the N.A. and some have a 0. The hyphen means unimportant, so can be used with or without. The 0 means no cover. As the N.A. rises, there is a very subtle blurring that takes place off axis as a result of spherical aberration, with moderate N.A. objectives. Objectives still work but the image tends to be progressively blurrier with higher N.A.s. Some objectives , due to their internal design are more tolerant, despite having the same N.A. as another that is severely affected. Generally speaking, the cutoff point is around .4 N.A. but I have seen ,90 N.A. objectives work o.k. but with some degradation. If you are going to invest in an APO , it would be false economy to buy into a no cover lens, even though they are a lot cheaper and in greater supply, than coverslip corrected lenses.. The resolution would be poorer than the cheapest achromat of the type.
My experience has been that diligence pays off. Keeping an eye peeled, eventually brings up the objective one wants at a low enough price , to be tolerated.

There are now some planfluorites being offered out of China. These are on the Olympus pattern for sure. Fluorites are often a better choice than apochromats, for the following reasons. They are usually within a hairsbreadth of the colour correction values of an apochromat. They are often within a hairsbreadth of the resolution of an apochromat. They offer a better working distance. They are much cheaper. There was a thread , a little earlier about the Chinese planfluorites, which are really attractively priced. Another option would be the Reichert planfluorites, made for the series 400. These will give 10% lower mag. than the Olympus objectives because they are corrected for a longer tube length but sometimes show up for really low prices. I would put one of them up against an apochromat any day.