If you attempt to dismantle a modern objective to examine or repair it there appears to be a high risk that it will perform badly.
For some information on the potential complexity of assembling a microscope objective see this post by discomorphella:
http://www.photomacrography.net/forum/v ... p?p=129865
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Received a Nikon MPlan 60x 0.70 objective. It was not the item illustrated and was damaged.
The seller immediately refunded the payment so I accept that mistakes happen. The seller did not want the objective returned.
First the usual pictures of the barrel design:
And the front element:
The front element has been smashed [it is cracked around much of its circumference] and has a deep and obvious gouge.
The element appears to have been decentred.
My first thought was that this may illustrate of how much damage an objective can sustain but still produce a serviceable [but probably reduced contrast] image.
It didn’t.
This is an uncropped stack of slime-mould spores [5DIII + extension tube set to give a mount-to-sensor distance of 200mm]. Even at this scale the definition of the objective is useless.
The outer barrel unscrewed easily. to reveal a familiar inner barrel. There was no evidence of thread locking compound.
The inner barrel has a chrome plated, annular screw cap which retains the stack of lens cells inside.
They are not the eleven individual elements, but six metal cells including the front and rear assemblies: all 17.95mm in diameter, plus one spacer ring and two thin shims.
I was surprised to see clear, old fingerprints on the metal cell sides [not mine! I handled the objective and lens cells with vinyl gloves]. I would not have thought that Nikon handled the cells during assembly without gloves so suspect that the objective had been opened before.
When the cell containing the front element was handled the lens element actually fell out.
The way lens surfaces and retaining rings protrude from the cells limits the number of ways they can fit together perfectly. The only potential ambiguity is the position of the spacer ring. However: to fit the patent this must be placed in front of the rearmost cell.
The outer surface of the rear element looks strange under oblique illumination: Is this just thin-film interference in the outer anti-reflection coating, or is it delamination of the coating ?
The appearance of the internal optical arrangement closely - but not quite exactly - matches example 1 [figures 1 and 4] of Nikon's US Patent 4,588,264 dated May 13 1986 credited to Yoshiyuki Shimizu
I have superimposed the patent drawing on the stack of cells. The fit is almost exact: better than it appears to be from these illustrations because the geometrical projections of a photograph of the stack and the orthogonal drawing in the patent are different. The ways in which individual convex elements and retaining rings protrude into adjacent cells all fit. The only difference I can see is that there is an air gap behind the front element in the objective but not in the drawing.
Although it’s rarely possible to be certain that a patent really does match a manufacturer product, this does appear to be close enough to be confident that this objective is based on the patent. Perhaps the design was re-optimised before production.
Observation 1:
The ray fan plot shows that the lens design is limited to a field number [image diameter at the eyepiece] of c.18mm. Beyond 18mm [a radius of 9mm on the plots] aberrations increase rapidly, just as seen in practice with most Nikon objectives from that time.
The 11 elements use nine different glass formulae. I have plotted them on a modern Schott Abbe diagram to show how diverse they are. [Other manufacturers produce equivalent glass maps]. One of the Nikon glass types is even off the edge of the current Schott chart [though charts from a decade ago do extend that far suggesting that the glass type has since been eliminated for environmental reasons]. The elements are numbered from the front.
Henry
