Is this aberration considered normal? (1 Viewer)

[takitam]

I have noticed a strange abberation with my Nikon HGL 8x20. Firstly I want to say it's not diffraction spikes- stars are pinpoints are many artificial light sources with 'covers' are as they should be.

The aberration I'm talking about is visible when I look at a street lantern, a type which has a 'naked' bulb visible in lower half, at night. When looking at it there is a narrow 'line' of light starting at the middle(from the bulb) and going both ways horizontally to the sides of FOV.

I find it strange because I only notice this problem with one type of street lantern, its not visible when I look at other light sources. Any comments about this, is it bins flaw?

 

[Kevin Purcell]

Despite what you say that's a diffraction spike from the roof edge of the roof prism.

The reason you don't see it with stars is stars are a lot less bright than a light so the diffraction spikes are a lot brighter too.

I'm not sure why you don't see it with other lights but a very bright point or line source shows this effect best.

It depends on the sharpness of the roof edge and varies across bins. I've tested a few with a naked mini Maglight bulb at 10m and it varies quite a lot though the better bins are better (on average).

Check each barrel and the magnitude of the spike may vary and certainly will vary in direction (as roof prisms are usually installed with the roof at 45 degrees or so to the "vertical" of the bin). Try blinking back and forth between eyes to see the effect.

 

[ronh]

I concur. The roofs I've seen had spikes at about 45deg, but there is no reason why a roof prism could not be rotated about the optical axis to some other angle. Any roof will do this more or less. A bare streetlight bulb is a brutal test.
Ron

 

[dalat]

I've got the same effect in mine as well. Its the roof edge. If you check one barrel alone, you will se a singel line only... I also only notice it on very bright light spots, otherwise it has not bothering effect...

 

[Kevin Purcell]

I concur. The roofs I've seen had spikes at about 45deg, but there is no reason why a roof prism could not be rotated about the optical axis to some other angle. Any roof will do this more or less. A bare streetlight bulb is a brutal test.
Ron

The reason they put them in at around 45 degrees is to avoid having the roof edge be vertical or parallel to man-made vertical and horizontal lines (think of the built environment) and so more likely to show odd effects on a tough test case.

Even cheap bins they seem to stick to this rule.

 

[ronh]

Well we're not much help are we? We think that it's from the roof prism edge, yet that has always been at 45 degrees in our experience. But, the claim is, it's horizontal. So, what gives? Either the prisms are rotated from the typical orientation, or it's something else.

Since the binocular apparently shows no 45 degree spikes, even under the harshest test, I "bet" the prisms are rotated oddly. But, my using the spikes to surmise the prism orientation is turning the problem over on it's head, I know!

We need another owner of that exact model to speak up.
Ron

 

[takitam]

Thank you for the clarification Kevin, Ron and Dalat.

It seems that I was wrong as I didn't know enough about diffraction spikes and I missed some points. When the bins are fully opened(max IP distance) the spikes are indeed 45' of the horizontal line. They're horizontal when I set the bins for me. I lied unintentionally, because I saw pictures showing different examples of this aberration, but fortunately Kevin catched it immediately.

Thanks for the lesson.

 

[Kevin Purcell]

The roof edges' aren't in at exactly 45 degrees ... the main points is they are manufactured like this to avoid vertical and horizontal alignments so 45 degrees plus or minus a bit is OK.

And they will rotate as you set the IPD.

A bare mini maglight makes a good test in a dark room (or a mercury light in the store). The sharper the edge the smaller the intensity of the diffraction spikes. So you can use this test to cherry pic bins though you should consider other features too(!). It might make a difference in contrast in bright conditions.

I've posted about these in the past as I found a Nikon Monarch that looked terrible in store with huge diffraction spikes (the industry style mercury lighting show this very nicely). I was amazed. These were the demo bins. Of course the counter help couldn't see the issue.

You can also see it sometimes (I saw it in the older Diamondbacks) in the "artificial star" generated by the sun shining off a convex surface like a a curved car's body. (Don't look at the reflection of the sun from a flat surface ... but I didn't need to tell you that ).

 

[hinnark]

The reason they put them in at around 45 degrees is to avoid having the roof edge be vertical or parallel to man-made vertical and horizontal lines (think of the built environment) and so more likely to show odd effects on a tough test case.

Even cheap bins they seem to stick to this rule.

BTW this is the reason why ISO resolution targets have two additional types of targets with bars in both 45° directions. USAF test targets are not enough to measure roof binoculars resolution. The roof line does effect resolution.

Steve