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BWBlackett

Manual Dob tracking and magnification

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Some newbie questions.

1. Using my 10mm eyepiece (giving x120 magnification) the planet moved across my field of view in about 20 seconds. I think that with a bit of practice I should be able to manually track by adjusting the Alt & Az. Does anyone have some tips on how to do this effectively?

2. Although the specs say my scope will give x500 magnification I would think that Saturn would fly by in a couple of seconds. Can someone with a 10" (or so) Dob give me some tips on the maximum magnification for looking at for example Saturn.

3. The view of Saturn 10mm (x120) was great. Am I right in thinking that with a 2x Barlow the planet will be twice as large in my eyepiece and take half tghe time to cross the field of view?

Thanks in advance,

Brian.

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1.) From my fairly limited experience with Dobs and 'nudging' I think its a case of practice makes perfect. I try to ensure the object is at one extreme side of the field of view and let it drift all the way through - eyepieces with wider fields of view will make this last longer but some eyepieces won't be too good at the edge so you may only get a few seconds of the best image you can get from the eyepiece.

2) It will fly! It'll also look pretty blurry unless you've got exceptional seeing and extremely good collimation! I tend to find that with the seeing I get here in Somerset that I can get to 200x quite easily, 250x sometimes, 300x occasionally and very rarely 400x.

3) Pretty much yes although doubling the magnification never seems to double the image size for me (perhaps someone can explain that one!)

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re: Maccers 3) A barlow doubles the focal length of the eyepiece, not the overall focal length, so the field of view of the ep stays the same. The image size should be larger, though. Perhaps it's a perception "thing".

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I didn't understand that either AM. Also ,I know it maybe spliting hairs but I've always thought of a Barlow as increasing the telescope focal length not the eyepeice focal length because they are used before the eyepeice optically and the eyepeice 'sees' an increased focal length that wasn't there before a Barlow was used. Widefield eyepeices can just be regarded as having Barlows/ Smyth lenses attached.

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Oops, halves the FL is correct. Doubles the magnification of the EP, does not affect the focal length of the scope.

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