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hi ive got a jessops 104 1100 telescope and in the focuser its got what looks to be a barlow lense (poor quility) ive taken it out and my image quility is vastly improved but if i place a 12.5 eyepiece in or smaller i cant focus in enough. i am wondering if i can get a smaller length focuser i am stuck at a loose end with this one. would be greatfull of any replies please.

Edited by nathanhatton

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It depends what you are trying to focus on and how far away it is. Are you doing this in the daylight on an object in the street? Or does this happen at night on a planet or other sky object? The 12.5mm eyepieces will give you 88x magnification. :)

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its the same with both. the barlow is built into the focuser if its taken out i can focus in with the 40mm or 20mm eyepiece but the 12.5mm my focuser wont wind in far enough and only needs to wind in one more turn to focus. if i put the lens back in i can focus fine with the 12.5mm and 6mm but the image quility is reduced? strange problem i know

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Not so strange Nathan - with a barlow you double the magnification so you'd be getting around 176x magnification wich requires a pretty clear sky and a small object (eg a planet). If you're looking towards the horizon you'll be magnifying atmospheric imperfections much more then aiming straight up high.

Seeing conditions in the UK on average limit us to around 180x to 200x and moments of perfect seeing occur very infrequently when you can go much above that. It also depends on the quality of the glass in the eyepiece and telescope optical quality. You also need to have it well collimated (optics lined up correctly).

I just noticed on the advert for your scope it says the barlow is 3x - that means you're using 264x magnification - way too much imho. Stick below 180x for now with the lower power eyepieces and you'll get on much better. Maybe a 2x barlow is more than enough for your scope :)

Edited by brantuk

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Thankyou for your reply. Yes there is a 3 times Barlow that fits into the focuser and don't use it that much because as you say there is too much light pollution. But my focuser actually has a little lens built in right at the bottom of its length no 1 seems to have heard of this. My uncle seems to think its to shorten the focal length of the tube but you take this little lens out and my problems start

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Barlows effectively elongate the focal length of the scope - a reducer will shorten it. Umfortunately some of the entry level scopes - notably from high street stores - require a barlow to make them focus properly with the supplied eyepieces.

They are ok for someone starting out in the hobby but some eyepieces can be virtually unusable with these scopes. It's good to practise with what you have then when you come to upgrade, ask lots of questions here and you'll get some great guidance on selecting your next scope and you'll know more about what you want it to do. :)

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Thankyou very much for your replies. Looks like il get to know the scope some more and get the hang of using it more then upgrade I can get some good views of the moon and Jupiter with it il have to see what else I can view properly thru it thanks again. :-)

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