Recommended Barlows

[prbaxter]

ok so I have a 2x barlow...

If I get a 3X barlow, can i use it with the 2x barlow and achieve 6x magnification or doesn't it work like that?

in which case, can you stack two 2x barlows up to get 4x, or even three of them...

if it does, can anyone recommend a good budget barlow?

Baxter.

[JamesF]

AIUI you can stack barlows to increase magnification, but on the other hand, yu have to ask yourself why you would want to do so. Every piece of glass you put in the light path loses some of the light so you'd probably be better off getting a better quality, shorter focal length eyepiece and using just that. The supplied Skywatcher barlow isn't that great and the 10mm EP isn't the best, so stacking more barlows in front is likely to be less than rewarding.

James

[prbaxter]

thanks.

Its mainly going to be for use with the spc900 webcam - and the moon. So I can increase gain and exposure to compensate for light lost, as well as stacking the images.

Baxter

[Steep]

Less but better quality glass is what you need, JamesF is right about you losing light and quality by stacking barlows. If you're after better images, stacking barlows is not the best way to go about it.

[prbaxter]

ok that helps. thanks people.

[brantuk]

Has been done sucessfully though - but gotta be with decent barlows like TV's

[prbaxter]

ok.. time to buy a barlow.

Which should I buy?

3x Barlow (Tal, possibly)

4x Barlow (a little over budget)

5x Barlow (Revelation)

I'm tending towards the 5x but maybe I'm just buying something I'll be selling again in a week or two...

???

decisions, decisions...

[JamesF]

Personally I think I'd go for the 3x and see how it works out. My gut feeling is that the 5x could mean that the image is quite dim and for imaging would need a lot of gain which in turn introduces noise. The 3x would probably be suitable for visual use too.

Basically, I think the higher the factor you go for, the bigger a gamble that the barlow will actually do what you want unless you've had a chance to try one first.

James

[lukebl]

If you're going for a 3x Barlow I'd strongly urge you to go for the Televue (see my own review here). Optically, they're brilliant, and you can simply add an extension tube to increase the mag to about 5x. As I said in my review, I really regretted getting rid of mine as it's a really superb piece of kit and perfect for webcam imaging. In my view, a 5x Barlow is not as flexible as a 3x one with an optional extension tube. I think they're on offer right now, too.

[prbaxter]

I didn't know you could use an extension tube with a barlow to increase it's magnification.

[sixela]

You do need some spare focuser in-travel, though (but less than the extension is long, fortunately).

[lukebl]

I didn't know you could use an extension tube with a barlow to increase it's magnification.

It's easy. Just remove the lens from your cheap old Skywatcher barlow, and insert it between the new barlow and the webcam. Inceases the distance from the cam to the barlow elements.

[JamesF]

Indeed. There's a bit more information here:

Barlow extensions

I've not tried it yet, but because I have an Ultima barlow as well I've removed the lens from my original skywatcher barlow, which isn't that nice anyhow, and I'm going to use that as an extension tube.

It's easy to remove the lens if you want to try it -- there are a couple of notches in the retaining ring that allow it to be unscrewed.

James