lense test?

Dear All,

I've just picked up a 2nd hand Nexstar 8i and want to compare the
optics/image quality with that of my ETX90 as quick as possible. With the
cloudy weather I've resorted to terrestrial viewing but immediately noticed
that the ETX90 produced a sharper picture. I'm not sure I approached the
test correctly however as both scopes where indoors and both used a 26mm
Plossel and as such perhaps I had unfairly hampered the larger Nexstar?
Although the Nexstar 8i was obviously producing a higher magnified image I
had expected it to be able to produce one just as sharp image? With the
object not being more that 150+ metres perhaps it was simply too close? In
short, yes it appeared clear but not razour sharp? Is this due to the
additional magnification x78 comapred with x48? Perhaps the larger scope
doesn't work well indoors compared to the littel ETX? Can any one explain to
me a simple method of testing the optics? I have a limited amount of time to
confirm I'm happy with the scope and will need to test ASAP probably as
noted under terrestrial conditions due to the weather.

Many thanks,

Mike

"Mike Cutts" wrote in message ...
Dear All,

I've just picked up a 2nd hand Nexstar 8i and want to compare the
optics/image quality with that of my ETX90 as quickly as possible. With the
cloudy weather I've resorted to terrestrial viewing but immediately noticed
that the ETX90 produced a sharper picture. I'm not sure I approached the
test correctly however as both scopes were indoors and both used a 26mm
Plossl and as such perhaps I had unfairly hampered the larger Nexstar?
Although the Nexstar 8i was obviously producing a higher magnified image I
had expected it to be able to produce one just as sharp image? With the
object not being more that 150+ metres perhaps it was simply too close? In
short, yes it appeared clear but not razour sharp? Is this due to the
additional magnification x78 comapred with x48? Perhaps the larger scope
doesn't work well indoors compared to the littel ETX? Can any one explain to
me a simple method of testing the optics? I have a limited amount of time to
confirm I'm happy with the scope and will need to test ASAP probably as
noted under terrestrial conditions due to the weather.

Many thanks,

Mike

Since nobody ese is having a go at this one: At the very least you
should attempt to match the magnification between the two instruments.
You have nearly a 2-1 ratio between the powers.
Don't expect anything at all from looking through a window. With the
window closed you are at the mercy of (possibly two layers) of mass
procuced glass between you and the object being viewed. With the
window open the indoor heat floods out through the open gap killing
the view stone dead.
According to amateur astronomer superstition. The sky is only cloudy
because you are considering another instrument. So you have only
yourself to blame! ;-)
Ask the seller for more time until the sky clears and match those
powers nearer to 100-120x for a more informed comparison. If the
seller is in a hurry then simply offer the 8i back. There is really no
substitute for testing on real astronomical objects in the night sky.
The moment you get a clear night you shouldn't even need a comparison.
The telescope will either perform and delight you. Or, it will not.

Chris.B

Your ETX is not user collimatable, and does not
normally need it. The Nexstar is collimatable and
will require checking reasonably often for optimum
views. It may well be that collimation is off
slightly.

Adam

--
Eschew obfuscation. Eliminate such idiom previous
to rejoining.
"Chris.B" wrote in message

om...
"Mike Cutts" wrote in
message ...
Dear All,

I've just picked up a 2nd hand Nexstar 8i and
want to compare the
optics/image quality with that of my ETX90 as
quickly as possible. With the
cloudy weather I've resorted to terrestrial
viewing but immediately noticed
that the ETX90 produced a sharper picture. I'm
not sure I approached the


Since nobody ese is having a go at this one: At
the very least you
should attempt to match the magnification
between the two instruments.
You have nearly a 2-1 ratio between the powers.
Don't expect anything at all from looking
through a window. With the
window closed you are at the mercy of (possibly
two layers) of mass
procuced glass between you and the object being
viewed. With the
window open the indoor heat floods out through
the open gap killing
the view stone dead.

Chris.B