telescope aperture size

please can you advise me.I recently bought a 3" [or 76mm] size reflector.

I have set it up no problem. But have I been cheated?

I understood that the aperture was a major factor in the usefulnss of a
telescope [I had previously owned a small one but not that useful for proper
astronomical observation].

Despite the size of the tube , the hole which collects light is very small and
SMALLER than my previous 'scope.

Is this usualin a reflector and can they really claim that it is a 3" telecope
when the hole at front in perhaps 2 in at most?

Thanks for any advice, Im recently coming back to this hobby and first bought
my small scope in 1972!

Keith

On Fri, 13 Aug 2004 09:55:04 +0000, Keithbcook wrote:

please can you advise me.I recently bought a 3" [or 76mm] size reflector.

I have set it up no problem. But have I been cheated?

I understood that the aperture was a major factor in the usefulnss of a
telescope [I had previously owned a small one but not that useful for proper
astronomical observation].

Despite the size of the tube , the hole which collects light is very small and
SMALLER than my previous 'scope.

Is this usualin a reflector and can they really claim that it is a 3" telecope
when the hole at front in perhaps 2 in at most?

It is done on the cheaper scopes, is it a ring that can be removed? Try
removing it. It reduces the light gathering ability of the scope.


Thanks for any advice, Im recently coming back to this hobby and first
bought my small scope in 1972!

Welcome back!

Keith

"Keithbcook" wrote in message
...
please can you advise me.I recently bought a 3" [or 76mm] size reflector.

I have set it up no problem. But have I been cheated?

I understood that the aperture was a major factor in the usefulnss of a
telescope [I had previously owned a small one but not that useful for
proper
astronomical observation].

Despite the size of the tube , the hole which collects light is very small
and
SMALLER than my previous 'scope.

Is this usualin a reflector and can they really claim that it is a 3"
telecope
when the hole at front in perhaps 2 in at most?

Thanks for any advice, Im recently coming back to this hobby and first
bought
my small scope in 1972!

Keith

This does sound very doubious to me. The apeture of a reflector is the
_smallest_ diameter of the light path from the front of the scope to the
primary mirror.
If the hole at the front of only 2" then it's a 2" scope, even if the
primary mirror is 3". You'll also loose a little quality because of the
spider that holeds the secondary mirror in place (but this isn't worth
worrying about)

Sorry, if this isn't what you wanted to hear. I could be wrong though.

OOps- just re-examined and found out the 2 inch cap is fixed on the 4.5 inch
cap covering the front [opposite mirror] end...but I am STILL puzzled:

[a] why does the larger black covering have a smaller cap attached to it
[previously I took off ONLY the small cap!]? and

[b] the covering measures 4.5 inches , the same size of the tube, but the scope
is a 3 inch reflector??
[c] my previous 'scope was refractor so had lens on front, but there is no
protection from dust etc in my reflector, how do I clean it when dust gets in??

sorry if these are obvious by I am a bit naive,

Thank you
Keith

Keithbcook wrote:

OOps- just re-examined and found out the 2 inch cap is fixed on the 4.5 inch
cap covering the front [opposite mirror] end...but I am STILL puzzled:

[a] why does the larger black covering have a smaller cap attached to it
[previously I took off ONLY the small cap!]? and

Because there are times, when you want to block some light: Observing the
sun.


[b] the covering measures 4.5 inches , the same size of the tube, but the scope
is a 3 inch reflector??

3 inch is the diameter of the main mirror. It is the main mirror which determines
how powerful your scope will be.

[c] my previous 'scope was refractor so had lens on front, but there is no
protection from dust etc in my reflector, how do I clean it when dust gets in??

Best would be: Don't
* don't let dust get in the tube. Always use the caps when you are not
operating your scope.
* don't clean the mirror if it isn't absolutely necessary. A few dust grains
will have next to no effect

As for methods of cleaning: eg.
http://www1.tecs.com/oldscope/atspages/techtips.htm


--
Karl Heinz Buchegger

Karl Heinz Buchegger wrote:

Keithbcook wrote:

OOps- just re-examined and found out the 2 inch cap is fixed on the 4.5 inch
cap covering the front [opposite mirror] end...but I am STILL puzzled:

[a] why does the larger black covering have a smaller cap attached to it
[previously I took off ONLY the small cap!]? and

Because there are times, when you want to block some light: Observing the
sun.

For heaven sakes - I forgot to mention:
Never, never, never observe the sun without some filter. Even if you reduced
the aperture with the means of the cap, the sunlight is still intense enough
to damage your eye seriously in a fraction of seconds.

--
Karl Heinz Buchegger

Tom Randy wrote in
news
Despite the size of the tube , the hole which collects light is very
small and SMALLER than my previous 'scope.

Is this usualin a reflector and can they really claim that it is a 3"
telecope when the hole at front in perhaps 2 in at most?

It is done on the cheaper scopes, is it a ring that can be removed?
Try
removing it. It reduces the light gathering ability of the scope.

Why would they deliberately reduce the effective aperture of the scope??

--
Steve Gray

thank you for your useful info - much appreciated

On Fri, 13 Aug 2004 15:51:25 +0200, Karl Heinz Buchegger wrote:

Karl Heinz Buchegger wrote:

Keithbcook wrote:

OOps- just re-examined and found out the 2 inch cap is fixed on the 4.5 inch
cap covering the front [opposite mirror] end...but I am STILL puzzled:

[a] why does the larger black covering have a smaller cap attached to it
[previously I took off ONLY the small cap!]? and

Because there are times, when you want to block some light: Observing the
sun.

For heaven sakes - I forgot to mention:
Never, never, never observe the sun without some filter. Even if you reduced
the aperture with the means of the cap, the sunlight is still intense enough
to damage your eye seriously in a fraction of seconds.


I'll also add NEVER,NEVER,NEVER use a screw into the eyepiece type "solar
filter". If you find one smash it and throw it away. They typically come
with cheap discount store scopes.

Steven Gray wrote:

Tom Randy wrote in
news
Despite the size of the tube , the hole which collects light is very
small and SMALLER than my previous 'scope.

Is this usualin a reflector and can they really claim that it is a 3"
telecope when the hole at front in perhaps 2 in at most?

It is done on the cheaper scopes, is it a ring that can be removed?
Try
removing it. It reduces the light gathering ability of the scope.

Why would they deliberately reduce the effective aperture of the scope??


To protect the cheap glas sun filter from overheating

--
Karl Heinz Buchegger