Joined: 05 Apr 2009
Location: Ohio, USA
|Posted: Mon Feb 14, 2011 12:06 am Post subject:
|This series of finite objectives--I think of them as the "MM" objectives, based on the naming of the microscopes they were intended for--ranges from 1x to 100x. The working distances are wonderfully long. The lower-powered MM objectives have fairly average NA's, while the higher powered MM objectives have rather large NA's:
1x NA 0.03 WD 79mm
3x NA 0.09 WD 75.5mm
5x NA 0.13 WD 64mm
10x NA 0.2 WD 49.5mm
20x NA .4 WD 20.3mm
50x NA .55 WD 15.1mm
100x NA .75 WD 4.1 mm
Nikon made these finite objectives for measuring microscopes used by toolmakers and their ilk. The objectives are part of the Nikon CF series, and so are corrected for chromatic aberration; they do not require an eyepiece or tube lens. Thus they are very workable on a bellows. They are very nice achromats--which is to say that they are pretty good, but do not compete with more expensive apochromats in terms of chromatic aberration. However, they generally exceed apochromats in terms of working distance.
These objectives first came to my attention as I perused old Nikon brochures and manuals. Wow, what working distances--must try! So I recently purchased the 5x MM objective in this series in order to test it.
My test was on a bellows against my Nikon 4/0.20 plan apo pushed to about 5x. This wasn’t a fair test, as the 4x has a higher NA and is an apo—and is expensive, hard to find, and simply the best lens I have ever seen at 4-5x. If I owned the widely-used Nikon 4x achromat, which has a comparable NA to this 5x MM objective, and is not an apo, it would likely have been a fairer test.
Not surprisingly, the 4x apo was better than the 5x MM, though with much less working distance. The 4x apo had higher resolution and no noticible CA. The 5x had some blue fringing in very high contrast areas, but one needed to look closely to find it. I’d rate the 5x MM as a good lens with enormous working distance, but not up to the quality of a more expensive apo with much higher NA (that would be asking a lot). The great strength of these measuring microscope lenses is their wonderfully long working distance. I do find the 5x MM an incredible pleasure to shoot with, because of the long, long, long working distance--macro was never easier.
I intended to post this out more carefully, with examples, but since this auction ends soon, I'm thinking that interested folks might want to study my original files right now. So here is a link to comparison files. Sorry that this link will expire in seven days, or after 100 downloads. If someone wishes to host it, please do so. But eventually, I'll take some actual pixel crops and post them out in their own thread.
If you download these files, you will see three files from each lens (scales of Urania ripheus). For each lens, you'll have ZS DMap and PMax files, untouched after stacking, and a Photoshop'd version of the DMap with heavy sharpening--I was quickly trying to see what could be brought out of each image.
Again, I'll stress that the 5x MM objective is here being compared with the best lens I'm aware of at this level of magnification. The 4x Nikon apo is, as far as I know, as good as it gets at 5x--and it is hard to find. I should also mention that the cone-shaped adapter for the 4x apo was very well flocked, while the cone-shaped adaper for the 5x MM was not. I intended to redo the test with proper flocking, which might well reduce flare and show an improved quality to the 5x MM lens. But since the current auction ends soon, I'll share what I currently have.
--Edited for typos
Last edited by Chris S. on Mon Feb 14, 2011 1:58 am; edited 1 time in total