New Barlow significantly reduces brightness

[Tosong (Daniel)]

Hi,

I recently bought a 3 element barlow from skies unlimited. I used it last night and was quite disappointed with the performance. The main thing was that it really reduced the brightness and made it hard to focus. I tried looking at Saturn and it wouldn't even focus. I'm almost at the limit of my scopes power (225 with a limit of 250) is this because it's a lousy barlow or is it because of my scope?

Cheers,

[Suzy]

Hi Daniel,

Very high magnification can darken an object. Saturn is a good example as you've found out.
Also, the quality of the "seeing" will determine how much magnification you can throw- the object will tend to shake and be hard to focus. All these things which you seem to be experiencing.
On very few nights can magnification be pushed that high to the limits of the scope.

Here's a guide as to how much magnification you can push per inch of apperture.

http://www.seqas.org/

[Tosong (Daniel)]

That's a relief then thanks for the advice Suzy!