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Which Barlow for planetry observation?


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Hi,

I'm sure that this question may have been answered previously on SGL, but can anyone tell me which particular Barlow I should get for planetry observation? Is a 3x or 5x more appropriate?

I know that everyone recommends a 2x, which I will get. I will be getting the SW 250p dob...

Thanks!

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I would say that a 5x is simply too much.

If you put a 10mm eyepiece in then it becomes a 2mm.

Saying that 5mm is as small as sensible in a 250p newtonian then you would start out with a 25mm eyepiee and a 5x barlow combination.

So any eyepiece less then 25mm would be of little use when used with the barlow. That does not leave much choice of eyepieces.

So the 3x seems most appropriate for actual use.

Edited by ronin
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I had the SW250 Dob and am a dedicated planetary observer. The SW250 is a really good planetary scope.

I found the best combination of eyepieces for this scope were 5mm and 6mm Radians. Both have wide fields and good eye relief. the 6mm gives x200 and the 5mm gives x240.

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The trouble is, a really good quality barlow costs as much as a decent eyepiece, although the barlow will work with a number of eyepieces of course.

I use the excellent Antares 1.6x barlow with my 8mm and 6mm eyepieces to give me 5mm and 3.75mm. The barlow cost under £50 (used) wheras the eyepieces would cost me £hundreds.

So it makes sense to me :D

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You don't need a barlow for visual ... modern long eye relief EPs mean that there's no benefit in them. Something similar is essential for increasing the image scale for lunar / planetary imaging. Don't waste money on anything but the best!

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You don't need a barlow for visual ... modern long eye relief EPs mean that there's no benefit in them.

There's no need for them. That's something else than saying there's no benefit in them (especially if you have a fairly sizeable collection of simple ortho, Pentax XO and TMB Supermono eyepieces).

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You don't need a barlow for visual ... modern long eye relief EPs mean that there's no benefit in them. Something similar is essential for increasing the image scale for lunar / planetary imaging. Don't waste money on anything but the best!

Mmm, me-thinks buying the 'scope is going to turn out to be just the first of many items; and not many of them will be cheap! No wonder astronomy is regarded as a hobby to last a lifetime! :)

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Mmm, me-thinks buying the 'scope is going to turn out to be just the first of many items; and not many of them will be cheap! No wonder astronomy is regarded as a hobby to last a lifetime! :)

Scopes seem to come and go but a good set of eyepieces can last a lifetime of observing.

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