concerned about my zeiss 7x42s

In all fields of observation I'm a sub-amatuer and pick up my binoculars rarely but always
with pleasure so I wonder if anyone can anyone throw any light on this? I purchased a
pair of Trinovid 8x20s about 20 years ago and for my very basic purposes have been quite
happy with them but always a little frustrated when casting around the night sky and
trying to get a broad and bright enough perspective so, on a whim and after trawling the
net for advice, I splashed out and purchased the zeiss 7x42s. I've had them for three
years or so and circumstances have seen to it that these have had nothing like the use
they deserve but I have picked them up a little more in the last few weeks. I notice now
when looking at a clearly visible planet that the image, while bright, is badly 'flared'
(there's probably a common-use word for the distortion I'm seeing if anyone can tell me
what it might be) and at no point resembles anything like a disc. The 8x20s however,
while showing the obvious light and fov limitations show the planet as a recognisable
circle - albeit very small but without any significant distortion. The stars through
both glasses are, of course, light points and in respect of viewing those the 7x42s show
no perceivable distortion and seem to provide only benefit - as one would expect. Does
anyone have any explanation for this. Are my 7x42s dud? Is there such a thing as a dud
Zeiss 7x42?
I should say when looking at the moon the image appears very sharp and I'm unable to
detect (my unaided eyesight isn't too bad though far from perfect) any distortion at the
edges of the moon image.

Any thoughts much appreciated.

I notice now when looking at a clearly visible planet that the image, while
bright, is
badly 'flared' (there's probably a common-use word for the distortion I'm
seeing if anyone
can tell me what it might be) and at no point resembles anything like a disc.
The 8x20s however, while showing the obvious light and fov limitations show
the planet as a
recognisable circle - albeit very small but without any significant
distortion.

The stars through both glasses are, of course, light points and in respect of
viewing those the 7x42s show no perceivable distortion and seem to provide
only benefit - as one would
expect. Does anyone have any explanation for this. Are my 7x42s dud?

There are two parts to this optical system, the binoculars and your eyes.

Those 7x42's have an "exit pupil" which is 6 mm in diameter, the 8x20's have an
exit pupil which is 2.5 mm in diameter. This is the diameter of the beam of
light in the eyepieces. Hold the binoculars up to a window and you will see a
bright circle in each eyepiece. This is what your eye sees.

With your eye open at night your own pupils will be open enough to admit the
entire 6mm beam from the 7x42's, maximum pupil dialation is usually considered
to be about 7 mm in young people, less in older.

Anyway, with your pupil wide open, you are using the entirety of your own eye
lenses. These are best at the center but often have defects and aberations
which are become apparent when the pupil is open like this.

Thus what you are likely seeing are defects in your own eyes. This is most
noticeable on bright objects like planets and bright stars like Vega and
Antares etc.

To find out if the "flares" are due to your own eyes or to your binoculars,
look at a bright star or planet through just one side of the bino. IF you see
a flare, then rotate the binoculars with respect to your head. If the flare
does stays with your head position, then the problem is in your eyes, if it
rotates with the binoculars, then the problem is with the binoculars.

In my case, the flares are caused by my own eyes and not the binoculars, my
guess is that this is your situation as well.

Best wishes and dark skies.

jon

novice wrote in


[snip
I notice now when looking at a clearly visible planet that the
image, while bright, is badly 'flared' (there's probably a
common-use word for the distortion I'm seeing if anyone can tell
me what it might be) and at no point resembles anything like a
disc. The 8x20s however, while showing the obvious light and fov
limitations show the planet as a recognisable circle - albeit
very small but without any significant distortion. [snip]
Are my 7x42s dud?
[snip]
Any thoughts much appreciated.


A possible explanation is that you have astigmatism in your eyes.
Astigmatism is less of a problem in daylight, since the error is
masked off when the pupils shrink. Your 8x20 binoculars have an
exit pupil of 2.5mm (20mm/8), so the astigmatism is masked off
however large your own pupils are, but your 7x42:s have an exit
pupil of 6mm (42mm/7) and in the dark your eye pupils open up and
the astigmatism shows.

I suggest you do either of two things (or both).
- Look through one barrel of the binocular, hold it still and
lean your head sideways, back and forth. Does the flare move
with your head or not? If it does, the problem is in your eyes.

- If you have spectacles with perscription adjusting for
astigmatism, try using them when looking through the binocular,
and see if the inage improves.


The stars through both glasses are, of course, light points and
in respect of viewing those the 7x42s show no perceivable
distortion and seem to provide only benefit.


That's strange! Can't explain that.

Cheers -- Harald

Any thoughts much appreciated.

What Jon said. BTW, I have the same binocular and I get the same
problem with Jupiter (tough picking out those moons with a flare on
them) and the brightest stars. It's simply astigmatism in my eyes and
that's what it most likely is in your case too. Otherwise I really
love my Zeiss 7x42!

You may wish to consider a bino with an exit pupil around 4-5 mm. My
current favorite quick look bino for astronomy is a Nikon Superior E
10x42.

Ritesh