New binoculars 12 x 50 roof prism

[clairete]

Well I have purchased my new binoculars Bushnell xlt 12 x 50. They have roof prisms. They are wonderfully clear and sharp (and almost too bright for the full moon) except when I view Jupiter which shows a little spike which moves as I move slightly.

Would this be because they are roof prism? Or could it be because of my not fabulous eyesight? In my younger years when I looked at the full moon I would see about 6 or more ghosty crescent "images" surrounding the sides and bottom of the moon - oddly this has improved with age (now 55 years young lol). I now see only 2 faint crescents.

I really like these binos but just wondering if I should have bought porros. Any thoughts?

[Peter Drew]

Hello Clairete. Welcome to this forum.

The Jupiter effect you describe can be caused by a number of things but 3 of them are the most likely.

1) The cementing together of the front lenses often causes distortions and hence "spikes" on stars and planets.

2) The roof line of the roof prism in some designs can show up as a spike but this would produce one each side of the object

3) A slight defect in the eye.

The effect of this problem is not usually noticeable for daytime viewing so is not a prime consideration for the manufacturers.  

[clairete]

Thanks Peter,

Had another look tonight and the spikes are indeed on both sides in the 12 x 50's as well as my 8 x 42's (both Bushnell XLT roof).

Still they are both excellent for day time viewing, no problem with stars or smaller planets (eg Venus and Mars) - just the big one, Jupiter! Which just happens to be the nicest one to view. Oh well.

I'm going to make an appointment with the optometrist to check my eyes too. See what he says.

Thanks again,

Cheers

Claire.