am i going wrong

[Guest hadden]

hi all.got me first scope today.telstar 900x114..i had a brilliant view of the moon a few hours ago.could see all the craters in real deatail.i came and had me tea and that was it, cant seem to focus correctly on it now.its a really clear night with the naked eye.is it something i am doing wrong?

[BAZ]

In response to your shoutbox comments, I would suggest making a home made dew shield for it, this can even be a bit of cardboard to get you by. A cheap camping mat and some duct tape will make a better one. it needs to be about 300mm long so there's plenty for it to grip to the tube of the scope. This will prolong your observing sessions.

[Guest hadden]

sorted.i will get on the dew shield 2moz.another newbie question.iv got 2 long eye pieces which have got "3x barlow lens" and "1.5x erecting eyepiece" and 2 shorts lenses's that go into the longer ones which have "sr4" and "h20" written on them..what should i be using for what???

[BAZ]

The X3 Barlow will probably be only any use with the Moon, what it does is alters the focal length of the eyepiece, by three, so a 10mm eyepiece would become a 3.33mm eyepiece. This would give you about 270X magnification, which is way past the capability of your scope. ( Focal length of scope, 900mm divided by by eyepiece focal length 3.33mm = 270)

The shorter one's are the eyepieces, SR 4 is a Symmetric Ramsden eyepiece, and to be honest I would try it on the Moon, if it's dark and has a poor view, put it safe in a draw and forget it. The H20, is a Huygens 20mm eyepiece, and will probably be the most useful, this will give you 45X magnification and would be a good eyepiece to mirror performance combination.

Hope that helps. Have a look at this, it's quite informative.

http://www.rocketrob...astro/first.htm

[Doc]

I would say your scope is a 900 FL divided by 114 Diameter equals F8

Your SR4 eyepiece I think is a 4mm so will give you 900mm divided by 4mm = 225x mag

This is good for splitting binary stars and planets

Your H20 will be a Huygen 20mm and will give you 900mm divided by 20mm = 45x mag

This is good for widefield views and is the one you use first to find your objects.

Your x3 barlow will turn your 20mm into a 6.4mm eyepiece and is NO good at all for your 4mm eyepiece as the mag will be stupid.

In my opinion your absolute mag you will be able to use is the 6.4mm I really think even though the scope was supplied with a 4mm eyepiece this is to much mag for your scope.

Posted same time Martyn.

[BAZ]

Same result though, sounds like we know what we are talking about.