andy middleton

Hi

Is there anyone out there who has a pair of Bresser Spezial Jagd 9x63 binos
who can comment on their performance. I am particularly interested in the
effective aperture of the 63mm objectives. I currently have a pair of
Bresser Linear (Meade) 9x63 binos and am disappointed that a plastic ring on
the inside of the objective lens reduces the effective aperture to a mere
56mm. Any comments would be much appreciated.

Thanks

Andy.

Don't buy the Bresser 9x56s ? ;-)
*
Chris.B

andy middleton

Any specifics are possible alternatives would be much appreciated.

Andy.

There is the possiblity that the ring you see is not stopping down the
objective lens as much as you think or even at all.

The objective is surely at least a doublet. As light rays pass through
the two lenses of the doublet, the rays are bent, converging. The cone
of light does not exit the back end of the doublet at the same diameter
the rays enter the front end. They do converge and more so than a
simple cone at the focal length of the binocular would show they
converge. Conceivably, for example, rays could be entering a 63mm
diameter doublet and exiting the back end of the doublet at only 55mm
before the light cone procedes to travel any further into the
binocular.

If the ring you see is wider than the diameter of the converged rays
exiting the back end of the doublet, then there is no light cutoff. If
you could focus the binoculars on infinity and then get a precise
measurment of the exit pupil (assuming magnification is as stated,
which is a broad assumption) you could perform a check on the effective
aperture. Don't close focus to test exit pupil as magnification is
always higher at close focus and exit pupil will always appear smaller.
So, in fact, the ring might not cut off any light at all.

edz

grimble gromble

[snip]

A cheap laser would soon show you what is, or is not, getting through - but
don't use your eye to check, use a piece of card.
Grim

but
don't use your eye to check, use a piece of card.
Grim


That would show you vignette in the prisms, but that would not show you
if the aperture ring is reducing the aperture. Checking magnification
and then checking exit pupil will verify effective aperture.

edz

Oops. It might. However, still, exit pupil and magnification will
verify exact effective aperture.

edz