Scope Barrel Length

[kim]

Hi All
Could someone explain the difference the viewing of objects with shor verses long barrel telescopes.
My scope is a Bushmaster StarExplorer SE114900, reflecting telescope (lens aperture of 114mm, focal length 900mm). Which has just snapped of the tripod mount Cheap stuff I guess. Anyway my girlfriend has just lent me her scope that she dosen't use anymore its a Meade eletronic GOTO 114mm, 1000mm, f/8.8 she said that it needs collimation even the moon diddn't focus to well {have instructions here on how to do this but it looks scary} the barrel length on my bushmaster measures 85cm long and on the Meade its about half as long 46cm could some one tell me which would be the better scope to view the planets through, I always thought that focal length was the length of your scope barrel.
Kim.

[Solanum]

Wouldn't want to comment on the best focal length for planetary viewing, but I imagine that the scope you borrowed is an SCT or similar in which case the light path is folded due to bouncing off the main mirror to secondary and back through the main mirror, thus the light travels the length of the tube twice, so the tube length is half the focal length.

[[1ponders] (Paul)]

Kim and
You are on the right track. The longer the focal length of the telescope (for a given eyepiece) the higher the magnification. Using a 20mm eyepiece with the 900mm focal length gives 45x mag, with the 1000mm gives 50x. In this situation you won't see much difference between the two scopes, but whack it into a 2500mm scope and you will notice the difference. Most people though use a 2X barlow rather than buy a 2500mm long telescope

As to why your 1000 is only half as long as the other, you will find that there is a built in 2x barlow in the focuser tube of that scope. This is a fairly common practice with lower end reflectors. These internal barlows don't normally have very good objectives either unfortunately.