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Hi I have the Orion XTI 8' Dob. telescope.  New to the telescope I bought a 4.7  82 degree eyepiece and a 2x barlow. Will this work well seeing planets and stuff?? Please help I am new to the telescope. Thank you

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Hi Joisme and welcome to this wonderful hobby

I would start with a much bigger eyepiece something like a 32mm as you will need to centre the object in the eyepiece and focus before you start to zoom in with smaller eyepieces and barlows.

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Thank you .. I have used my barlow with the 10mm that came with it.  I was able to do that.  I just hope the 4.7 and the barlow will work with my telescope well

 

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Hello and welcome to the forum.

The XTI 8 has a focal length of 1200mm so a 4.7mm eyepiece will give a magnification 255x. This might be good for the moon, Saturn and Mars on nights of very good seeing but often might be too much magnification so a slightly longer focal length eyepiece (say 7mm for 171x) would be a better choice. The barlow lens will double the magnification that a particular eyepiece gives so will give too much magnification when used with the 4.7mm eyepiece, or even a 7mm.

 

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Sorry still learning how to use this telescope... It is so different from my 1st telescope... a meade ETX 80mm autostar computerized... 

This Orion 10018 SkyQuest XT8i IntelliScope Dobsonian Telescope  I am trying to learn. kinda confusing.  Would love any advise and help I can get

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There is lots of advice on this forum about the 8 inch F/6 dobsonian telescopes. They are very popular in the Skywatcher, Orion and other brandings.

This thread might help with the choice of eyepieces:

Don't get carried away with very high magnifications. Much observing is done at low or medium magnifications (ie: 30x, 50x, 70x, 100x). For the planets, the moon and double stars 130x - 200x are very useful but over 200x not so much and 300x or more extremely rarely.

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18 minutes ago, Joisme said:

Thank you. for all your advice.  

You are welcome :smiley:

Keep asking the questions - there are lots of experienced folks who like to help here :thumbright:

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I do have another question but dont want to sound stupid. Sometimes when looking to find the planet on my telescope. I am not sure where to align it so I can view it . is it normally to the right of the X ?  Sorry.. with my old telescope I just had to type it in example moon.. then just view. with the dob i cant..  sorry I know practice will make it better but I just get frustrated sometimes. 

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You need to make sure that the X (cross hairs) in your finder are pointing in pretty much exactly the same place as the view through the scope is. There are adjustment screws on the finder to adjust it's tilt. A good way to do it is, in daylight, find a target a mile or so away such as a telegraph pole or similar, get that in the centre of view in the scope, then adjust the tilt of the finder scope, as needed, to get the same target in the centre of the view in that.

Not a stupid question at all.

 

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Makes sense will try that now. thank you again

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As mentioned above, the 4.7mm eyepiece will deliver 255X magnification, which will be good for planetary viewing during most conditions on a 8" telescope. Using it with the 2X barlow will deliver 510X which is over what 99% of seeing conditions will allow in general and definitely over the useful magnification on a 8" telescope. I find that on my 8" SCT 406X (5mm eyepiece at a 2032mm focal length) if the limit that delivers great views, BUT mind you this is during the best seeing conditions.

A 6mm eyepiece with your 2X barlow will deliver 400X, check out the televue Nagler series, they are some of the best and clearest eyepieces I have used, along with a LV, but the Televue Nagler the field of view is double of the LV.

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Welcome from land down under

When doing schools and cubs/joey's with my astronomy club

I use 17mm wide-angle eyepiece in my 10" dob

Gives good eye relief and when viewing Jupiter, able to see moons clearly

Most dobs only come with a 25mm and 10mm eyepieces

Enjoy your adventure

 

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Posted (edited)
On 14/06/2018 at 00:10, John said:

Hello and welcome to the forum.

The XTI 8 has a focal length of 1200mm so a 4.7mm eyepiece will give a magnification 255x. This might be good for the moon, Saturn and Mars on nights of very good seeing but often might be too much magnification so a slightly longer focal length eyepiece (say 7mm for 171x) would be a better choice. The barlow lens will double the magnification that a particular eyepiece gives so will give too much magnification when used with the 4.7mm eyepiece, or even a 7mm.

 

I was going to ask the FL of the scope. A 4.7mm EP+2X barlow!!!!!!!.

Thats gonna need some exceptionally clear steady seeing to be used. 255x magnification is very doable in an 8" scope. Not sure a 4.7+2x is the best way to get it. 

Edited by LukeSkywatcher

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On 14/06/2018 at 00:10, John said:

Hello and welcome to the forum.

The XTI 8 has a focal length of 1200mm so a 4.7mm eyepiece will give a magnification 255x. This might be good for the moon, Saturn and Mars on nights of very good seeing but often might be too much magnification so a slightly longer focal length eyepiece (say 7mm for 171x) would be a better choice. The barlow lens will double the magnification that a particular eyepiece gives so will give too much magnification when used with the 4.7mm eyepiece, or even a 7mm.

 

Agree with the above. My 10” dob also has a focal length of 1200 and I do find my 7mm eyepiece is the most frequently used for planetary observing. I will go higher when the seeing is particularly good but the 7mm is always the first into the focuser for the planets. 

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