Barlow/scope limitations.

[Fandango]

I have seen for sale a GSO 2.5x barlow and GSO 5x barlow for only about £5 more. I wondered if my scope 'size' would somehow determine what barlow I'd be able to use? I'd appreciate a little advice please.

[Naemeth]

With that scope, the highest magnification you'll ever realistically get is x260 anyway, it's best to get a 2x and a nice range of EPs. On the very very very rare night, you'll be able to push your scope beyond 260x, but that's highly unlikely, I believe a 5x is useful for Astrophotography though.

[swamp thing]

+1

The 5x Barlows are really imaging tools. They very quickly run out of eyepiece options for visual use IMO.

[JamesF]

Agreed. You might get some use out of the 2.5x if you want to push the magnification close to the theoretical limit, but you'd probably get more use out of a wider range of eyepieces and a 2x barlow if required.

James

[greyknight]

Hi all. I have a 2 x barlow which I'm very happy with and was going to get a 3 x and a 5 x but having read your comments I may not gain much from it. My scope came with a 10mm and 2mm EP would I get better results from 4mm/6mm etc?

[greyknight]

sorry that should've read that it came with a 10mm and 20mm not a 2mm!

[JamesF]

What telescope is it?

James

[greyknight]

Hi its a Celestron 130 EQ

[Naemeth]

I'm not sure on their claims of Highest Magnification being 307x.... I'd go with more what the OP's is (and they might get a higher practical magnification with a Parabolic mirror) of 260x.. so same applies really, you would be better off with a range of EPs. I'd go for at least a 6mm and 8mm. Or just an 8mm, you might find more use with it

[JamesF]

In that case the usually-accepted maximum magnification will be 260x (twice the aperture). The focal length is 650mm, so the maximum useful focal length for an eyepiece would be 650/260, or 2.5mm.

How often the seeing is good enough to achieve 260x magnification is open to debate, but assuming "not very often" woukldn't be a bad place to start, so were I in your position wanting greater magnification from that scope I'd be tempted to look at adding an eyepiece in the 7.5mm to 6mm range and using a 2x barlow to double the magnfication with that eyepiece when required.

I've no idea what the 10mm eyepiece shipped with the Celestrons is like. The one Skywatcher use certainly doesn't have anyone raving about it. If the Celestron is the same then you might find that replacing it with a decent one and adding a 2x barlow to get you a 5mm equivalent is a better place to start, then make a decision about a shorter focal length eyepiece to give you two more options after that.

James

[greyknight]

Brilliant advice guys thanks very much.

[Naemeth]

You might want to eventually add a wider one, maybe 25mm and 15mm, but they are for later, EPs can get rather expensive rather quickly.