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Nikon Fieldscope 60 EDIII Prism (1 Viewer)
- Thread starter mayoayo
- Start date
looksharp65
Well-known member
http://www.birdforum.net/showthread.php?t=133149&highlight=ED82+EDIII
See henrys post (#2). I recall I have seen a picture of them both beneath each other. It can have been a BF member who used the EDIII for digiscoping, then bought the ED82. I think his pictures were on Flickr. Anyway, the prism housings seemed identical.
//L
See henrys post (#2). I recall I have seen a picture of them both beneath each other. It can have been a BF member who used the EDIII for digiscoping, then bought the ED82. I think his pictures were on Flickr. Anyway, the prism housings seemed identical.
//L
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looksharp65
Well-known member
mayoayo
Well-known member
Hi Lars..thanks..I was pretty sure of this ,but not completely ..First I thought the oversized prism maybe was only for the ED82 and the 60 could have used a slimer version,but i got that pretty much sorted looking at some nikon brochures...Now I have the confirmation...
looksharp65
Well-known member
Hi!
The scopes are the straight versions, but I assume that the angled share the same prisms as well.
//L
NDhunter
Experienced observer
Rick:
This does bring up an interesting topic. I am accustomed to just the
straight models, in several of the Nikons, from the ED50, FS III, and the
ED 82.
How do the angled models differ, and with the angle needing an extra
prism to bend things, I am thinking they are losing some light somewhere.
I do not recall this topic of angled vs. straight scopes has been explained.
As far, as different coatings, dielectric, and any advantage with one over
the other, I do want to learn more.
Maybe someone here can shed more light. In my mind the straight scope
would easily be the best optically.
Jerry
RJM
Don't Worry, Be Happy!
Jerry, Henry and Kimmo have explained it in several threads over the years. I think at the time the ED82 was introduced their design did offer a brightness advantage over its peers. Much in the same way Zeiss claims a benefit from using Abbe-König prisms in their Victory FL 42mm and 56mm bins. Yet I doubt many folks will see a brightness difference between the Victory and an EDG or Swarovision.
henry link
Well-known member
Jerry,
There's more than one way to make an angled scope. The 60, 78 and 82mm Nikon fieldscopes used a monoblock Schmidt prism that was oversized and offset so that the roof edge did not split the light cone. That kind of prism has only 2 glass to air surfaces and 4 reflections like a Porro, all with total internal reflection. It needs no phase correction or mirror coating.
The 50mm angled Fieldscope uses a Porro followed by a semi-pentaprism. That has 6 glass to air surfaces and 6 reflections, one of which requires mirror coating.
IMO the new angled Fieldscopes have taken a step backwards. They use centered Schmidt prisms, so the roof edge splits the light cone. They require phase correction, but not mirror coating.
Henry
There's more than one way to make an angled scope. The 60, 78 and 82mm Nikon fieldscopes used a monoblock Schmidt prism that was oversized and offset so that the roof edge did not split the light cone. That kind of prism has only 2 glass to air surfaces and 4 reflections like a Porro, all with total internal reflection. It needs no phase correction or mirror coating.
The 50mm angled Fieldscope uses a Porro followed by a semi-pentaprism. That has 6 glass to air surfaces and 6 reflections, one of which requires mirror coating.
IMO the new angled Fieldscopes have taken a step backwards. They use centered Schmidt prisms, so the roof edge splits the light cone. They require phase correction, but not mirror coating.
Henry
NDhunter
Experienced observer
Henry:
Thanks for the explanation, now it sounds quite easy to just make the angled
scope without much trouble. In your last mention, I am thinking you are
referring to the EDG fieldscope, and the new construction. Have you had
a chance to evaluate the EDG scope?
Jerry
mayoayo
Well-known member
Henry..Thanks for the explanation...I see also the point explained by RJM about the new options offered by dielectric and modern Phase correction offering alternatives to that design...
I personally like the form-ergonomics derived of this design ,with the eyepiece coming out to the side of the prism box..It leaves a clear path to aim the scope and offers a nice assymmetric left-right configuration,adding an interesting and unique aesthetic ,specially with the Fieldscope focuser design ...I guess the centered phase coated prism of the EDG can be proportionally smaller and lighter,...or did they put the prism in the center to get a determined look?
I personally like the form-ergonomics derived of this design ,with the eyepiece coming out to the side of the prism box..It leaves a clear path to aim the scope and offers a nice assymmetric left-right configuration,adding an interesting and unique aesthetic ,specially with the Fieldscope focuser design ...I guess the centered phase coated prism of the EDG can be proportionally smaller and lighter,...or did they put the prism in the center to get a determined look?
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henry link
Well-known member
Jerry,
I haven't seen the new EDG scopes, but changing from an offset to a centered Schmidt prism creates new opportunities for optical defects that the old scopes never had. The new arrangement requires high precision roof angles, a well made roof edge and phase correction. All of that comes at a higher cost and a higher risk of defective specimens. The other current alpha scopes also use centered Schmidt prisms and I've already seen a few badly made roof edges in star tests. It was impossible by design for the old Fieldscopes to have that defect. You could say the same thing for the change from Porro to Schmidt-Pechan roof in the straight versions of the EDG scopes.
Henry
mayoayo,
Yes, the centered prisms can be smaller and lighter, but I doubt that the difference amounts to more than a few ounces.
I haven't seen the new EDG scopes, but changing from an offset to a centered Schmidt prism creates new opportunities for optical defects that the old scopes never had. The new arrangement requires high precision roof angles, a well made roof edge and phase correction. All of that comes at a higher cost and a higher risk of defective specimens. The other current alpha scopes also use centered Schmidt prisms and I've already seen a few badly made roof edges in star tests. It was impossible by design for the old Fieldscopes to have that defect. You could say the same thing for the change from Porro to Schmidt-Pechan roof in the straight versions of the EDG scopes.
Henry
mayoayo,
Yes, the centered prisms can be smaller and lighter, but I doubt that the difference amounts to more than a few ounces.
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looksharp65
Well-known member
Yes of course. What I meant was that the EDIIIA and the ED82A use the same prisms, like the EDIII and the ED82 share another prism design.
Jason Bugay Reyes
Well-known member
Henry,
Very interesting !
I have a question, when Nikon changed from Porro to Schmidt-Pechan roof in straight EDG scope, that's the reason the scope body is straight like telephoto lens than the ED scope which is offset to the top ?
Can Nikon still use Porro on straight EDG scope ?
henry link
Well-known member
The answer to the first question is yes.
I'm not sure I understand the second question. A Porro could easily have been used in the straight EDG scopes, just like Swarovski and Kowa do. I don't know why Nikon chose to switch to a Schmidt-Pechan prism, since there's no optical advantage and the size and weight difference is negligible.
Jason Bugay Reyes
Well-known member
What I mean is, would the EDG straight scope design still the same if it uses Porro than Schmidt-Pechan roof ?
RJM
Don't Worry, Be Happy!
Hi Jason, I think if you look carefully you will see the difference the prism choice makes.
With the straight ED82 the eyepiece is vertically offset from the objective lens barrel just like a porro prism binocular. This offset is different from the horizontal eyepiece offset of the angled ED82.
With the straight EDG85 however, the eyepiece is totally in line with the objective lens barrel, just like a roof prism binocular. I suspect Nikon chose this prism solution to make the EDG seem more camera lens-like. Plus they get to use the popular "dielectric coating" catchphrase in their ads!
With the straight ED82 the eyepiece is vertically offset from the objective lens barrel just like a porro prism binocular. This offset is different from the horizontal eyepiece offset of the angled ED82.
With the straight EDG85 however, the eyepiece is totally in line with the objective lens barrel, just like a roof prism binocular. I suspect Nikon chose this prism solution to make the EDG seem more camera lens-like. Plus they get to use the popular "dielectric coating" catchphrase in their ads!
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