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hi everyone just ordered five new plossl eyepieces from scopes and skies the sizes are 6.3 mm 10mm 15mm 20mm and 40mm can someone advise me which would be the best to use with a x2 barlow lens these are the first ones i've bought so can i have a honest opinion if anyone has bought them from this supplier and what they think of them many thanx jimmythemoonlight :)

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The 40mm barlowed with a x2 will give 20mm - you already have one of those. The 15mm and 10mm are probably the best to barlow - you will get 7.5mm and 5mm with the x2 barlow. Barlowing the 6.3mm will probably give too much magnification but that does depend on the scope you are going to use them with, as Spaceboy suggests.

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The maximum magnification of your scope is x260 ( seeing often only allows for a max of x200 )and the lowest magnification is x18.57

6.3mm = x142

10mm = x90

15mm = x60

20mm = x45

40mm = x22.5

You will be able to x2 barlow all but the 6.3mm which would be way beyond the capabilities of your scope.

HTH

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As John says, the 10mm and 15mm will be the ones to use with a barlow. The 15mm with the barlow will give 120x which will probably be about the best you will get from your scope unless you have really good sky conditions.

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:icon_salut:cheers for that sorry i didn't give you all the info here goesi have a 5" skywatcher 130p hope that will be enough info the focal length is 900mm which i think is a f/6

Hmmm - not quite - the 130P has a focal length of 650mm

Do you have a 130 instead? (no "P") - that one is 900mm...

(there's normally a sticker with this information stuck on the telescope body next to the eyepiece holder)

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it is definately 900mm so i may have made a mistake i just thought that all 130's were p's it has the focal length on the side of the tube it also has d 130 as well as f 900 i hope this ends your confusion thanx for everything great bear and also a big thanx to spaceboy as well as rik Mcrae for his input this site is a really good site people on here dont care how thick you are they just give you the info you want many thanx one and all jimmythemoonlight :rolleyes:

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The "P" is for the mirror shape; it stands for "parabolic" (the curve on the mirror cross-section). Without the "P" it's a spherical curvature on a 900mm mirror, but I think they probably had to move over to a parabolic mirror when reducing the focal length down to 650mm on the shorter scopes.

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Do spherical mirrors have to have a corrector? I read that the images lack the sharpness of a parabolic mirror.

I think it depends on the focal ratio and the aperture. At around f/10 with a 5" mirror the difference between spherical and parabolic is negligible so no correction is needed.

Regards Steve

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