probably a dull barlow question

[sparkyjon]

i have a x2 barlow and a x3 barlow if i put them together does that make them a x5 barlow,

i might be making an exit from the forum if it's a really stupid question , but i'm still learning magnification and focal length and aperture,,

[JamesF]

No, they multiply. Together they'd be the equivalent of a 6x barlow.

James

[sparkyjon]

ah right so is a x6 barlow useful for anything

[Merlin66]

Hmmmmm not really!

It would take your magnification way to high, unless you were using a 40mm + eyepiece.

Sometimes, just sometimes, when doing planetary imaging a x5 barlow would be useful - one night a year??

[sparkyjon]

That's what i was thinking planetary with a web cam. Well Tge are there i can just try and have a play.

[Merlin66]

Over the years I've collected many barlows/ powermates etc - for spectroscopy and double stars....( I think I have more barlows than eyepieces!)

In my limited experience of planetary/ solar imaging I've found working above f25 or so un-rewarding. if you have an f5 scope and a GOOD x5 barlow/ powermate then you'll get good results. Just my 2c.

[JamesF]

Most of my planetary imaging thus far I have done at around f/35 (with my SPC900) and if I recall correctly Martin Mobberley suggests going out as far as f/40, but I think if you're considering using a 6x barlow something in your brain ought to be asking if you're actually using the right tool for the job, and there's no point pushing the image scale way beyond the effective resolution of the telescope or camera.

With my new camera with 3.75um pixels I think I'll be dropping that back to f/20. I'm not sure there's any advantage in pushing things any further with the smaller pixel size.

James

[stem1989]

Its the equivalent of a 6x and the magnification would be way past what is your scopes highest, unless of course you decide to take the scope into low earth orbit at some point