Using a Barlow/magnification

[JamesF]

I was up late last night watching Saturn using a 6mm Celestron Omni ep and whilst the image was ok it was also very small, so I thought I'd try the Barlow supplied with the scope to see if that improved things. Unfortunately if anything it made the image worse.

Given the 80mm aperture I'd expect the maximum reasonable magnification to be 160x and with a 400mm focal length and 6mm ep I believe the magnification should be 67x, so doubling that still doesn't seem to be too extreme.

Am I asking too much here, or is it likely that atmospheric effects were just limiting the performance I could expect? Or, is the Barlow supplied with the ST80 just not that brilliant?

James

[John]

With your Startravel 80 I think 100x is pushing it to be honest - the chromatic abberation produced by the F/5 achromats does get in the way of their high power performance. Supplied eyepieces and barlows are generally basic at best (thats why they can supply them !) so you may see some improvements with better quality eyepieces but they won't transform the scope into something it's not.

The 160x figure is a theoretical maximum and would be more realistic for an F/10 - F/12 80mm refractor under excellent conditions.

The ST80 is a nice low to medium power, grab and go scope though

[JamesF]

Fair enough. I'm still trying to get my head around all the relationships between aperture size, focal length, magnification and resolution. It seems it's never quite as simple as the books tell you...

Thanks,

James