(Nikos Aslanakis) wrote in sci.astro.amateur:

My wife gave me as a present a "do not ever by this!" department store
70/700 scope wich came with 2 eyepieces, a Kellner 4mm an a SR 20mm.

The 4mm gave 175x which was over the recommended (140x) magnification
for the scope.

It realy hooked me into astronomy so I decided to buy a 11mm Televue
Plossl eypiece witch was a big improvement and today I bougth a
Celestron Ultima Barlow 2x.

The 11mm TV gave me 64x so with the barlow I shoud get 128x which
should be just fine for the apperture.

BUT when I try the 11mm TV with the Barlow on Mars I get a BIGGER
planetary disk than with the 4mm eyepiece. I can tell this because
with my other eye I can compare the planet to the holes on the tripod.
And yes I put the barlow after the diagonal.

What happens here? I suppose 175x is bigger than 128x. Is this right?
What am I missing?

If the description on the eyepieces and on the barlow as well is
correct, and your scope is f 700mm the magnification with a 2x barlow
indeed is 700/5.5 as opposed to 700/4.

If you are absolutely certain that this is no visual effect, and not due
to a smaller FOV of the Plossl (maybe 60 deg versus 50 degrees), there's
only one conclusion left: the labels on the eyepieces are wrong. Maybe
the 4mm Kellner is a low end "department store accessory" and in the
Chinese factury they switched the plastic label - after all, probably no
one there could reach that latin-symbol gibberish..... :P

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