Joined: 14 Mar 2009
Location: Near London, UK
|Posted: Tue Apr 04, 2017 1:57 pm Post subject:
|Two thinkgs make 20x difficult
1) Working distance
10x objectives usually have at least several mm. 20x, don't, unless they're LWD or ELWD or SLWD (Long, Extra, Super)
2) "Biological" objectives are designed to be used with a glass cover slip - the 0.17mm part. At low NAs, below (say) 0.3 or a little more, it doesn't make a visible difference.
At about 0.4 or higher, it starts to.
At 20x, most microscopy is with transmitted light, from a condenser, through a transparent - ish specimen.
OR, it's metallurgical, then the subject is dead flat, and WD doesn't matter, and lighting doesn't matter much.
Also most objectives need corrective eyepieces (like your Olympus did) which is a pain on a camera - you can get various amounts of CA.
So there aren't many objectives to choose from.
New, they're all expensive.
Don't forget about finites, because you only need to arrange an empty, non reflective tube.
If you reverse a short lens on a long one, as I expect you know, if you focus both at infinity the magnification is
FLlong / FLshort.
Yes you can try a cine lens, security camera lens, microfiche lens, of 10mm or so on a 200mm. The WD will be very short, though, and most of them aren't designed for high resolution applications.
Old lenses can be good, but most aren't a large enough aperture to be really good. They were better for their intended purpose - large film.
Diffraction is the problem.
You should search here, and online; there is masses!
The effective aperture is what matters.
A 20x, NA 0.4 objective, is working at EA
20/(2*0.4) = EA 25
A simple 10mm FL lens to give that same EA at 20x would have to be
25/(20 +1) = f1.19 AND be working WELL at that aperture. A tough call!
EVEN THAT is too small an aperture for small pixels - your sensor will have more pixels than necessary.
And what about Carl Zeiss Jena 15 mm f2.3 Mirotar x18-32
Leitz photar 12.5 mm f1.9 x12.5 - 40
Zeiss West Germany Luminar ii 16 mm f 2.5 x10-40
Nikon U20 8mm f1.5
Macro Nikkor 19 mm f 2.8 x15-40 Are these lenses finite or infinite?
The Photar and Nikon (horribly expensive for what it is) should be reasonable at about 10x but above that, you'd get too much diffraction for a small sensor.
I would suggest you get a 10x finite or infinite objective.
As you have a "tube" lens, try infinite.
Either one of the Nikons in the FAQ thread, or a Mitutoyo/Olympus depending on your budget and willingness to try used objectives, which can be a nightmare.
You'd get 15x on your 300mm, with a "20x" infinite objective. They're designed for Tube lenses around 200mm.
If you have tubes/bellows to get to 150mm (-200mm) between sensor and objective flange, there are MANY respectable FINITE objectives for little money, say 10x NA 0.25. They're cheap. Some should need compensation, but much can be achieved in Photoshop, and they're fun
Lomo, Melles Griot, Reichert, Watson, Vickers, Amscope.....
Some of the current Chinese objectives , finite and infinite, aren't bad for their sub-$50 price.
The Nikon 10x NA 0.3 finite objective was regarded as about the best, for a long time.
Joined: 06 Sep 2011
|Posted: Tue Apr 04, 2017 2:26 pm Post subject:
|One thing I'd urge a little caution on - I personally found 20x an order of magnitude more difficult than 5-10x. It seems as if you're jumping straight in there but you might get discouraged at first.
I don't want to put you off, but with 20x there is no room for forgiveness if you have any camera shake, and you might find that you also need some other infrastructural apparatus like a solid stacking stage (ie large breadboard or aluminium t slot), lights like Ikea Jansjo or other more expensive lighting, and some sort of sledge be it mechanical or electronic. Ie it's not just the optical part that you'll need to think about - but also all the other apparatus that is part of a 20x setup. If you've got all this, great. If not, it bears consideration.
My extreme-macro.co.uk site, a learning site. Your comments and input there would be gratefully appreciated.
Joined: 01 Apr 2017
|Posted: Tue Apr 04, 2017 11:43 pm Post subject:
|Thank you Lou Jost, for putting me in the right direction.
For the old Nikkor A1-200 mm prime lens, what infinite microscopelens would you suggest to buy to reach 20:1 enlargment, for really good resolution ?