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Glass types in NL Pure-series (1 Viewer)


Well-known member
Short answer.

With traditional polishing the curves are pretty good and consistent.

The figure 3 Newton rings.

Astigmatism may be a problem.

In bulk polishing the lenses at the edge are less good than in the centre.

Modern high speed polishing is considerably less accurate and modern standards have slipped.

The exotic glass is more likely in the eyepieces for the original question.

Who the maker is determines quality.

As to getting curves from x-ray images my personal opinion is that it is a non starter.


henry link

Well-known member
I thought I'd juxtapose the 8x42 NL X-ray with a cutaway of an 8.5x42 EL SV to see what differences would stand out. I tried to make the sizes as close as possible by using the objective apertures as references. The lens curves don't appear to be very useful, especially in the X-ray where concave surfaces and cementings don't show much or at all, but the diameters of elements and stops do show how the wider FOV of the NL was accomplished by using larger prisms with wider stops and a much larger eyepiece field group.

You can see how the edges of the larger NL prisms come quite close to the body walls compared to the EL, especially at the narrow waist. The only really significant lens difference I see in the NL, besides its bigger eyepiece field group, is a thinner focusing element. Apparent differences in lens curvatures may just result from the way the cutaway slices the curves at the lens centers while the X-ray mostly shows only the thickness of the edges with only convex surfaces standing out.

I'll just mention again that whatever glass types are used in NL are very effective at correcting both longitudinal and lateral CA in the test set-ups I use to evaluate them.



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Well-known member
United States
Thanks Henry, seems like my wandering wonder is answered. The lens sure appears like the curve is concentric, (not sure thats visible this way). The right image with the light path, infers (to the left one), there's room for the light to bounce here and there through the prism, and exit in line with the lens centers.

Confess I was thinking about my eyeglasses that correct for a large astigmatism and the understanding they have an offset or rotated optical center/axis, (which I cant see looking at them).

That idea about NLs seems put to rest.
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Well-known member
IMO I don't think there has been a significant change in overall performance in the last 10 years. I have handled many a premium glass made from 2000. By the way both the SF and NL are flat views like the SV or the EDG, just done a bit different.
Granted the FOV has increased and started with the SF in 8 and 10X42 a few years ago, and the EII which I enjoy has always had almost 9 degrees FOV. If anything, the ER has increased for the benefit of those who wear glasses.
Agreed! Forget to add I wear glasses so that pretty much influenced my perspective opinion.

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