tenex
reality-based
That agrees with my experience: porros were more tolerant of IPD setting, and roofs seem more finicky now. And we live in a roof prism era, though I do still have a great old Zeiss porro.
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How to set IPD accurately? (8 Viewers)
- Thread starter tenex
- Start date
That agrees with my experience: porros were more tolerant of IPD setting, and roofs seem more finicky now. And we live in a roof prism era, though I do still have a great old Zeiss porro.
Alexis Powell
Natural history enthusiast
I've tried w/my glasses off and I still have no problem, despite facial asymmetry. I am convinced more than ever that the issue you are confronting is a bin with too large a diameter of eyecup for your eye-nose configuration. That is a problem independent of IPD, and it shouldn't be something that poses a problem when using bins with smaller diameter eyecups.
--AP
I don't see what the type of prism has to do with setting IPD.
Could you explain.please?
tenex
reality-based
I experience partial blackouts with many/most binos today (especially when scanning the FOV) that I don't recall from decades ago, and don't have with my own old porro. I don't actually know that the prism type is the cause, but in any case I'm trying to minimize it by careful setting of IPD.
An undersized roof prism could cause truncated exit pupils. This would make the IPD setting more critical.
Bob
But isn't that equally true of an undersized porro prism?
Will that not also truncate the exit pupil?
I don't know that answer. I never ran into a Porro prism with undersized prisms. My main experience with Porro prisms is with the Nikon 8x30 and 10x35 E2s and they have oversized prisms.
Robert Olech, who runs Allbinos, has mentioned in a number of his binocular reviews of roof prism binoculars that their truncated exit pupils could have come from undersized prisms. For instance, it is mentioned in the next to last paragraph of his review of the 10x42 Vortex Viper HD binocular.
https://www.allbinos.com/240-binoculars_review-Vortex_Viper_HD_10x42.html
Bob
PS: I should mention that I own and use all 3 Nikon SE Porro prism binoculars and that they all use the same prisms; in fact they use the same prism housing and oculars. Only the objectives and objective tubes differ.
In these binoculars the FOV decreases from 7.5º in the 8x32 to 6º in the 10x42 to 5º in the 12x50.
I really don't know if it is possible to have this "truncation" in a Porro prism. I never gave it any thought until you brought it up.
Robert Olech, who runs Allbinos, has mentioned in a number of his binocular reviews of roof prism binoculars that their truncated exit pupils could have come from undersized prisms. For instance, it is mentioned in the next to last paragraph of his review of the 10x42 Vortex Viper HD binocular.
https://www.allbinos.com/240-binoculars_review-Vortex_Viper_HD_10x42.html
Bob
PS: I should mention that I own and use all 3 Nikon SE Porro prism binoculars and that they all use the same prisms; in fact they use the same prism housing and oculars. Only the objectives and objective tubes differ.
In these binoculars the FOV decreases from 7.5º in the 8x32 to 6º in the 10x42 to 5º in the 12x50.
I really don't know if it is possible to have this "truncation" in a Porro prism. I never gave it any thought until you brought it up.
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This https://www.cloudynights.com/topic/173374-undersized-prisms-the-myth/ may be relevant.
It would seem to me to have truncation of the exit pupils from undersized prisms you would have to have some kind interference that would "shave" off or "block" a portion the "light cone" while it passed through the prisms to the eye piece. I don't even know if that is possible at all.
Can anybody who knows what they are talking about in this matter jump in here and clarify things?
:brains:
Bob
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The discussion I cited addressees this by talking about the f Ratio of the objective, and the angle of the entry cone into the prism, rather than the light path through the prisms.
AFAIK the f Ratio of the SEs stayed the same and the angles of their entry cones into the prisms remained unchanged. Their FOVs decreased accordingly. There is no distortion of their exit pupils.
I noticed in the above linked CN discussion that the OP in his first post was talking about undersized exit pupils, not truncated exit pupils.
The 3rd comment seems to get into what might cause "truncated" (the word used is vignetting) exit pupils:
"The issue of prism size is important in one area only: that it allow a reasonably illuminated edge-of-field for the chosen ocular. A big field stop diameter, as for wide angle designs, requires a commensurately large prism. But the prism aperture can actually be a bit smaller than the field stop diameter and still deliver an image that has no detectable vignetting."
But he says "a bit smaller."
Bob
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