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zanti-misfit
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Reged: 08/17/09
Posts: 88
Loc: SE United States
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I've been doing a lot of reading and studying on the ins and outs of binoculars lately. Used Edz "The Score" testing and graph to choose a pair (Pentax 8x40 WPII for me) and found the information helpful and useful. However, when I came to the issue of vignette and illumination I got a little blurry eyed..
The results confuse me and I absolutely admit I'm a newcomer to this stuff, so please forgive my ignorance in advance. haha
So vignette effects illumination correct? The amount of light actually making it from the objective, thru the prism system, into the EP deals with vignette? So if its tilted and stuff the illumination rating goes down? Is that the main purpose of testing for that?
Now I'm sure I missed something already..but if that's true to some degree then why did the Pentax 8x40 still score very highly in the illumination category? Out of 34 binocs tested only 9 scored 4 or better (out of 5) with this one being in that range. So is that related to the design and size of the EP making up for the losses from the tilted beam? If that's the case then what's the big deal with a lower vignette test? I'm confused.
For example, in that battery of testing the Nikon SE 10x42 scored a good score of 4.1 for vignette yet scored a 3.5 illum, lower than the Pentax. And with the Fujinon FMT-SX 10x70 scored a 3.9 vign but had a 3.0 illum rating..  lol Is the size of it's exit pupil (not sure what it was now) causing that lower illum rating, or maybe the increase in mag (though I would think the 70mm apeture would make up for that).
I'm here to learn. If the design of the binoc gives a high illum rating despite the losses with less than perfect vignette capability why does it matter? Is there something else being lost by poor vignette scores that I don't understand? There must be something else besides illumination issues that I'm missing. Please school me on this issue. 
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 14731
Loc: Cumberland, R I , USA42N71.4W
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among others
things that are accounted for by vignette
mis-sized baffels
too small prism aperture
inside of barrel intruding into light cone
prism walls intruding into light cone
tilt of light cone in the system
things that can contribute to illumination or lack of
prism walls
tilt in the system
varying the quality of glass in lenses and prisms
quality of coatings
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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zanti-misfit
member
Reged: 08/17/09
Posts: 88
Loc: SE United States
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Perhaps a vignette/illumiation ratio could be devised to help indicate when vignette losses are truly degrading performance of a particular pair of binocular's illumination performance into the red zone.
If a system can keep a relatively high illum rating, despite vign issues, I'd not have called it a super negative overall. Now the illum rating perhaps "could have been" higher if the vign system was better devised..but if the illum level is already in the green I might not have been so heavy with the red ink, across the board, with overall scoring perhaps.
Some certainly do seem to suffer from the vign, but others didn't despite the vign numbers.
But again, I'm nowhere near as experienced and familiar with the specs and testing methods as you are of course, just a young "grasshopper" to you "Sensei" haha 
Thanks for chatting about it and trying to clarify the issue for me. I love this stuff, so fascinating! 
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GlennLeDrew
Pooh-Bah
Reged: 06/18/08
Posts: 1283
Loc: Ottawa, Ontario, Canada
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Here's a way to begin to understand vignetting.
Look through a paper towel tube, positioning your eye about as far behind the rear end as the tube is long. For example, if the tube is 10 inches long, hold the tube so that the near end is about 10 inches from your eye. As you move your eye to the left or right, observe how the front hole becomes cut off by the rear hole's edge. That's vignetting!
That paper tube is a good example of a telescope or binocular. The front hole is the objective, and the rear hole represents either the innermost opening of a telescope's focuser tube or the front aperture of a prism group. As you move your eye around, imagine that your eye is located at the eyepiece's field stop (the circular aperture generally immediately in front of the eyepiece, and which is seen as the sharp-edged circle framing the view as you look into the instrument.)
If you wish, you could go one step further and make a kind of mock-up which includes all three critical apertures:
- Objective. Make the hole 4 inches wide.
- Front prism aperture. Make this hole 2 inches wide.
- Eyepiece field stop. Make this hole anywhere between 1-3/4 to 2-1/2 inches wide.
Lay out the mock-up so that the prism hole is about halfway between the objective and field stop holes.
Happy experimenting!
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Home-made 11X50 right angle bino, 8.1 deg. FOV
Modified 26X100 bino, 3.5 deg. FOV
Home-made Mk II RA bino, using interchangeable objectives and eyepieces
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