Edges brighter than the center - why? (1 Viewer)

[jafritten]

Good evening! Here's a good question: Why is it that when I look through my Ultravid 10x32 HD the center appears markedly darker than the edges? I only notice it when I scan the skies for high flying birds. In photographic terms I'd say the center (about 2/3 of the field) is about 1/3 EV darker than the edges. This phenomenon is not present in the UV 7x42+ - I have checked that - and I haven't noticed it in any other binocular.

I am not really bothered about it, I am just curious to know.

Any ideas?

 

[Tringa45]

Strange. Almost all binoculars vignette towards the field edge.
Try holding the Ultravids at arm's length and slowly turn off axis. Usually the round exit pupils become almond-shaped, or at best gibbous moon shaped before occluding.

John

 

[jring]

Hi,

my money is on slightly off eye placement - so not quite kidneybeaning (which also can occur as a black spot in the center).

So try to vary your eyecup extension a bit... a bit less or a bit more (easier said than done - for starters try to rest the eyecups on your brow... if that helps, maybe make an extension from bicycle inner tube or out a layer of sponge rubber on the eyecups).

Joachim

 

[jafritten]

Strange. Almost all binoculars vignette towards the field edge.

You're right, John. Both my 10x32 and 7x42 vignette towards the field edge. After some experimenting as suggested by Joachim and you I found that what I have actually observed is a bright corona-like ring around the center. By contrast, the center seems darker.

I examined both binoculars again and found that this phenomenon is actually more pronounced in the 7x42. I had never noticed it until you and Joachim made your suggestions. There's no sign of a bright corona when I look through my 7x42 like I usually do. But as I move it away from my eyes in a linear direction - 2, 3 or 5 centimeters - , the phenomenon becomes apparent.

With my 10x32 the effect is slightly different. I think I observed this effect in my 10x32 first because the effect occurs when I bring it up in the right position. Finding the right position (eye placement) is not always as easy with the 10x32 as with other binoculars. So that might account for my impression it was a phenomenon unique to the 10x32 UV.

What I see reminds me of an eye with a wide open pupil and a corona or halo around it. Unfortunately, I cannot examine my other bins at the moment.

I'd like to know if you all see something similar.

 

[Maljunulo]

If everything looks concentric, I don't see how it can be bad eye placement.

 

[jafritten]

If everything looks concentric, I don't see how it can be bad eye placement.

It's the distance between the exit pupil and my eye. At the right distance the phenomenon does not exist, it only occurs as I alter the distance between exit pupil and my eye. See Joachim's post #3.

 

[Maljunulo]

It's the distance between the exit pupil and my eye. At the right distance the phenomenon does not exist, it only occurs as I alter the distance between exit pupil and my eye. See Joachim's post #3.

My bad ....... I interpreted "bad eye placement" as off axis.